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Nanotechnology Highlights - Institute of Physics by linfengfengfz

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									NaNotechNology
     iopscience.org/nano


    Highlights 2011
Why publish with Nanotechnology?
1. HIGH IMPACT
The growth in the number of published articles has been accompanied by an impressive increase in the
impact factor. Nanotechnology has an impact factor of 3.652 as listed by the ISI 2010 Science Citation Index
Journal Citation Report.

2. FAST PUBLICATION
Our peer review process is rigorous and efficient, with an average receipt to first decision time of just 23 days.

3. WOrk WITH THe BeST IN THe WOrLd
Nanotechnology features top research from institutions throughout the world; only 20% of submitted articles
are accepted for publication.

ANd THAT’S NOT ALL…
By publishing your paper with Nanotechnology you can take advantage of a number of other benefits
including:

• Free for 30 days
  All articles published in Nanotechnology are free to read for all, for the first 30 days following publication.

• nanotechweb.org
  Additional promotional opportunities are available on our sister website nanotechweb.org, which is viewed
  by more than 53 000 people per month.

• Widely read
  More than 1.5 million Nanotechnology articles were downloaded in 2010.

• Fantastic visibility and exposure
  The journal will be represented at more than 50 conferences in 2012.

• Open access
  The option to publish articles in open access format.

dO yOU WANT TO kNOW MOre?
To find out more about publishing with Nanotechnology, please visit iopscience.org/nano
or contact the journal team at nano@iop.org.
                                                                                                                   Nanotechnology Highlights 2011




 Impact factor                                 Dear colleagues,
  4.0

                                               It has been a big year for Nanotechnology. Still one of the few weekly publications in
    4.0
                                               the field of nanoscience and technology, the impact of the journal is continuing to grow.
   4.0
                                               The 2010 impact factor (as listed in the ISI Journals Citation Report) rose to 3.652, the
  3.0
                                               highest so far. The result is particularly pleasing in view of the large number of papers
    3.0
                                               published in comparison with other journals in the field.
   3.0

   0                                           A stricter editorial policy is in place. Only around 20% of submitted papers are accepted.
        2006 2007 2008 2009 2010
                                               An increase in editorial filtering before peer review has helped us to ease the strain on the
      0
         2006 2007 2008 2009 2010              researchers we use as referees, as well as minimizing delays. Despite the large number of
      0
1 6000002006 2007 2008 2009 2010               papers submitted each week, most still receive a first decision within 23 days of receipt.
 yearly downloads

  1600 000
1 200 000                                      We are also refining the journal’s scope. An emphasis on potential technological
  1 600000
                                               applications is required for papers to be considered for Nanotechnology. This is in line
  1200 000
 800 000
 1 200 000
                                               with how the journal is generally perceived in the community, and clarifies our position
                                               in a field that continues to expand and develop with research from a large range of
   800 000
 400 000
   800 000                                     disciplines. Another amendment to the scope is the introduction of a new energy
   400000
       0
                                               section in spring 2011. This is dedicated to all fundamental insights and technological
         2006 2007 2008 2009 2010
   400 000                                     innovations that advance energy generation and storage.
          0
              2006 2007 2008 2009 2010
          0
              2006 2007 2008 2009 2010         A number of new online features for material in the journal are imminent as part of
                                               IOP Publishing’s article evolution program. These include a new functionality for viewing
 Subject distribution
                                               articles on IOPscience as a HTML page, video abstracts and a zoom function for images.

                                               Nanotechnology continues to receive considerable recognition in the general media and
                                               a number of press releases over the year have helped to ensure that our articles feature
                                               regularly in the public eye. Recognition has also been afforded to a former Editor-in-Chief
                                               of Nanotechnology, Mark Welland, who received a knighthood in Queen Elizabeth’s
   Biology and medicine                        birthday honours in the UK.
   Electronics and photonics
   Energy and nanoscale
     Biology and nanofabrication
   Patterning and medicine                     This highlights brochure provides just a taster of the leading research in the field over the
     Electronics medicine
     Biology and and photonics
   Sensing and actuating
   Materials:andand photonicsassembly
     Electronics nanoscale
     Energy synthesis or self                  past year. And of course there’s plenty more where that came from at
     Patterning nanoscale
     Energy andand nanofabrication
   Materials: properties, characterization
     Sensing and actuating
   orPatterning and nanofabrication
      tools                                    www.iopscience.org/nano.
     Materials: synthesis or
     Sensing and actuating self assembly
     Materials: properties, self assembly
     Materials: synthesis orcharacterization
     or tools
     Materials: properties, characterization
     or tools                                           Mark Reed
                                                        Editor-in-chief, Nanotechnology
                                                        E-mail nano@iop.org
 Cover image: The relationship between                  iopscience.org/nano
 the size of the area of interaction
 (rnc non-contact mode) and the fraction
 of the energy dissipated (p) for an
 interaction force at d=1nm and for
 R=20 nm. Sergio Santos et al 2011
 Nanotechnology 22 345401.




                                                                                                                                  Nanotechnology   3
Nanotechnology Highlights 2011




Contents
Biology and medicine
A conceptually new type of bio-hybrid scaffold for bone regeneration                                                                         9
A Tampieri, E Landi, F Valentini, M Sandri, T D’Alessandro, V Dediu and M Marcacci



Surface functionalization of PLGA nanoparticles by non-covalent insertion of a homo-bifunctional spacer for active
targeting in cancer therapy                                                                                                                   9
S I Thamake, S L Raut, A P Ranjan, Z Gryczynski and J K Vishwanatha



Amphiphilic polymer-coated hybrid nanoparticles as CT/MRI dual contrast agents                                                               9
Dongkyu Kim, Mi Kyung Yu, Tae Sup Lee, Jae Jun Park, Yong Yeon Jeong and Sangyong Jon



Control of neuronal network organization by chemical surface functionalization of multi-walled carbon nanotube arrays                        10
Jie Liu, Florence Appaix, Olivier Bibari, Gilles Marchand, Alim-Louis Benabid, Fabien Sauter-Starace and Michel De Waard



A novel cationic liposome formulation for efficient gene delivery via a pulmonary route                                                      10
Peng Li, Donghua Liu, Xiaoli Sun, Chunxi Liu, Yongjun Liu and Na Zhang



Depth-sensing nano-indentation on a myelinated axon at various stages                                                                        10
Wei-Chin Huang, Jiunn-Der Liao, Chou-Ching K Lin and Ming-Shaung Ju



electronics and photonics                                                                                            Sponsored by




Improved conversion efficiency of CdS quantum dots-sensitized TiO2 nanotube array using ZnO energy barrier layer                             12
Chong Chen, Yi Xie, Ghafar Ali, SeungHwa Yoo and SungOh Cho



Combined micro- and nano-scale surface textures for enhanced near-infrared light harvesting in silicon photovoltaics                         12
Chia-Hua Chang, Peichen Yu, Min-Hsiang Hsu, Ping-Cheng Tseng, Wei-Lun Chang,Wen-Ching Sun, Wei-Chih Hsu, Shih-Hsin Hsu and Yia-Chung Chang



Magnetization dynamics, Bennett clocking and associated energy dissipation in multiferroic logic                                             13
Mohammad Salehi Fashami, Kuntal Roy, Jayasimha Atulasimha and Supriyo Bandyopadhyay



Large scale, highly conductive and patterned transparent films of silver nanowires on arbitrary substrates and their
application in touch screens                                                                                                                 13
Anuj R Madaria, Akshay Kumar and Chongwu Zhou



Optical properties of quantum-dot-decorated polymer nanofibers                                                                               14
Huaqing Yu, Rui Zhang and Baojun Li



Capacity based nondestructive readout for complementary resistive switches                                                                   14
S Tappertzhofen, E Linn, L Nielen, R Rosezin, F Lentz, R Bruchhaus, I Valov, U Böttger and R Waser




4   Nanotechnology
                                                                                                                                    Nanotechnology Highlights 2011




energy at the nanoscale
Reversible degradation of inverted organic solar cells by concentrated sunlight                                                                                         16
Thomas Tromholt, Assaf Manor, Eugene A Katz and Frederik C Krebs



Obviating the requirement for oxygen in SnO2-based solid-state dye-sensitized solar cells                                                                               16
Pablo Docampo and Henry J Snaith



Nanosilicon in water as a source of hydrogen: size and pH matter                                                                                                        16
Bernhard Goller, Dmitry Kovalev and Olga Sreseli



Hydrogen storage inside graphene-oxide frameworks                                                                                                                       17
Yue Chan and James M Hill



How localized are energy dissipation processes in nanoscale interactions?                                                                                               17
Sergio Santos, Victor Barcons, Albert Verdaguer, Josep Font, Neil H Thomson and Matteo Chiesa



Supercritical fluid deposition of vanadium oxide on multi-walled carbon nanotube (MWCNT) buckypaper for supercapacitor                                                  17
electrode application
Quyet Huu Do, Changchun Zeng, Chuck Zhang, Ben Wang and Jim Zheng



Patterning and nanofabrication                                                                                                   Sponsored by




Nanoimprinting lithography of a two-layer phase mask for three-dimensional photonic structure holographic fabrications                                                  19
via single exposure
Di Xu, Kevin P Chen, Kris Ohlinger and Yuankun Lin



Fabrication and characterization of bit-patterned media beyond 1.5 Tbit/in2                                                                                             19
Joel K WYang, Yunjie Chen, Tianli Huang, Huigao Duan, Naganivetha Thiyagarajah, Hui Kim Hui, SiangHueiLeong and Vivian Ng



Spin-wave interference patterns created by spin-torque nano-oscillators for memory and computation                                                                      19
Ferran Macià, Andrew D Kent and Frank C Hoppensteadt



Focused ion beam-fabricated Au micro/nanostructures used as a surface enhanced Raman scattering-active substrate
for trace detection of molecules and influenza virus                                                                                                                    20
Ying-Yi Lin, Jiunn-Der Liao, Yu-Hung Ju, Chia-Wei Chang and Ai-Li Shiau



Rapid turnaround scanning probe nanolithography                                                                                                                         20
Philip C Paul, Armin W Knoll, Felix Holzner, Michel Despont and Urs Duerig



Single and multilayer metamaterials fabricated by nanoimprint lithography                                                                                               20
I Bergmair, B Dastmalchi, M Bergmair, A Saeed, W Hilber, G Hesser, C Helgert, E Pshenay-Severin, T Pertsch, E B Kley, U Hübner, N H Shen, R Penciu, M Kafesaki,
C M Soukoulis, K Hingerl, M Muehlberger and R Schoeftner



                                                                                                                                                                    )



                                                                                                                                                       Nanotechnology    5
Nanotechnology Highlights 2011




Sensing and actuating
A carbon-nanotube-based sensor array for formaldehyde detection                                                                    22
Yijiang Lu, M Meyyappan and Jing L



Multi-physics damage sensing in nano-engineered structural composites                                                              22
Roberto Guzmán de Villoria, Namiko Yamamoto, Antonio Miravete and Brian L Wardle



Surface imaging using holographic optical tweezers                                                                                 22
D B Phillips, J A Grieve, S N Olof, S J Kocher, R Bowman, M J Padgett, M J Miles and D M Carberry



Silicon nanowire arrays as learning chemical vapour classifiers                                                                    23
A O Niskanen, A Colli, R White, H W Li, E Spigone and J M Kivioja



Mass and stiffness calibration of nanowires using thermally driven vibration                                                       23
D R Kiracofe, M M Yazdanpanah and A Raman



Periodically porous top electrodes on vertical nanowire arrays for highly sensitive gas detection                                  23
Hyun Jin In, Christopher R Field and Pehr E Pehrsson



Materials: synthesis or self-assembly                                                                               Sponsored by




Selective-area catalyst-free MBE growth of GaN nanowires using a patterned oxide layer                                             25
T Schumann, T Gotschke, F Limbach, T Stoica and R Calarco



Utilizing boron nitride sheets as thin supports for high resolution imaging of nanocrystals                                        25
Yimin A Wu, Angus I Kirkland, Franziska Schäffel, Kyriakos Porfyrakis, Neil P Young, G Andrew D Briggs and Jamie H Warner



Role of proteins in controlling selenium nanoparticle size                                                                         25
J Dobias, E I Suvorova and R Bernier-Latmani



Electrostatic and capillary force directed tunable 3D binary micro- and nanoparticle assemblies on surfaces                        26
G Singh, S Pillai, A Arpanaei and P Kingshott



Hydrothermally grown ZnO nanostructures on few-layer graphene sheets                                                               26
Yong-Jin Kim, Hadiyawarman, Aram Yoon, Miyoung Kim, Gyu-Chul Yi and Chunli Liu



Direct growth of tellurium nanorod arrays on Pt/FTO/glass through a surfactant-assisted chemical reduction                         26
Hongmei Liu, Boming Zeng and Falong Jia




6   Nanotechnology
                                                                                                                          Nanotechnology Highlights 2011




Materials: properties, characterization or tools
The synthesis of newly modified CdTe quantum dots and their application for improvement of latent fingerprint detection                                   28
Feng Gao, Jiaxing Han, Jun Zhang, Qun Li, Xiufeng Sun, Jincheng Zheng, Liru Bao, Xin Li and Zhiliang Liu



Improvement of toughness and electrical properties of epoxy composites with carbon nanotubes prepared by                                                  28
industrially relevant processes
R Hollertz, S Chatterjee, H Gutmann, T Geiger, F A Nüesch and B T T Chu



Force scanning: a rapid, high-resolution approach for spatial mechanical property mapping                                                                 29
E M Darling



Laser treatment of solution-deposited carbon nanotube thin films for improved conductivity and transparency                                               29
Myungo Joo and Myeongkyu Lee



Magnetic properties of nanomagnetic and biomagnetic systems analyzed using cantilever magnetometry                                                        30
Urs Gysin, Simon Rast, Andreas Aste, Thanassis Speliotis, Christoph Werle and Ernst Meyer



Probing near-surface nanoscale mechanical properties of low modulus materials using a quartz crystal resonator atomic                                     30
force microscope
Yen Peng Kong, Ling Chen and Albert F Yee



Media coverage
The switching location of a bipolar memristor: chemical, thermal and structural mapping                                                                   31
John Paul Strachan, Dmitri B Strukov, Julien Borghetti, J Joshua Yang, Gilberto Medeiros-Ribeiro and R Stanley Williams



Mirage effect from thermally modulated transparent carbon nanotube sheets                                                                                 31
Ali E Aliev, Yuri N Gartstein and Ray H Baughman



editorial board
Editorial board and team members                                                                                                                          32




                                                                                                                                         Nanotechnology    7
Nanotechnology Highlights 2011




Biology and medicine
The axe and leeches of ancient medicine have given way              functionalization of polymer nanoparticles with the
to a number of less invasive and more sophisticated                 protein annexin A2 by non-covalent insertion of a homo-
treatments. When it comes to navigating the intricacies             bifunctional chemical crosslinker for targeted cancer
of biological systems, the scale and properties of                  therapy. Overexpression of annexin A2 in cancer cells
structures and techniques used in nanotechnology have               has been shown to lead to metastasis and migration.
obvious advantages.                                                 Attaching the annexin A2 antibody to the nanoparticles
                                                                    as a targeting moiety enhanced the release of the drug
Researchers in Taiwan have used nano-indentation to                 curcumin. The cellular uptake of nanoparticles was also
characterize the structure of the multilayered myelin               significantly higher in annexin A2 positive cells than in
sheath, the layers of fatty membrane that enfold an                 negative cells. The results demonstrate the potential
axon and play a critical role in the transmission of nerve          use of this method for nanoparticle functionalization
impulses. They identify three stages in myelination.                and delivering chemotherapeutic agents for cancer
The method can be used to evaluate the development                  treatment.
stages of myelination or demyelination during nerve
regeneration.                                                       Cationic liposomes have recently proved effective gene
                                                                    carriers. Researchers at Shandong University in China
In Italy researchers have presented a conceptually                  have prepared a cationic liposome with a narrow particle
new approach for bone regeneration. They prepared                   size distribution and strong DNA binding capability. The
bio-hybrid hydroxyapatite/collagen scaffolds by a                   liposome proved less cytotoxic than other liposomes
biologically inspired mineralization process. The                   with comparable transfection efficiency. Intratracheal
researchers incorporate magnetic nanoparticles                      instillation further improved the efficiency for pulmonary
directly during the stage of hydroxyapatite nucleation.             gene delivery.
The magnetic nanoparticles become an intrinsic
component of the scaffold considerably improving the                The potential for applying nanotechnology in disease
biocompatibility.                                                   diagnosis and treatment is clear. This selection of
                                                                    highlights underlines just how far research has come in
Researchers in Texas in the US report the surface                   realizing that potential.




                             Section scope
                              This section of Nanotechnology focuses on the forefront of nanoscaled materials and
                              techniques in biological and medical research. Biological applications of nanotechnology
                              have garnered significant attention in recent years for their potential benefits in emerging
                              fields of biotechnology and medicine, and consequently this section includes some of the
                              most-read and most-cited articles in the journal. We welcome submissions of innovative work
                              in a variety of fields including but not limited to the use of nanoparticles as delivery vehicles
                              for drugs or gene therapies, nanoscale materials for directing cell phenotype and function,
    Section Editor: Jeff Karp nanoscale materials used in tissue engineering and regenerative medicine, nanostructured
                              medical devices, the use of DNA to create useful materials, the development of nanoscale
    approaches for biosensing or diagnostic applications, the use of nanomaterials for probing biological processes,
    investigations of the metabolic behaviour and biosafety of nanotechnology and novel methods for high-resolution
    cell and tissue imaging. Published material covers both in vivo and in vitro investigations, maintaining excellent
    standards of novelty and interest.




8    Nanotechnology
                                                                                                                                             Nanotechnology Highlights 2011




                                                                      A conceptually new type of bio-hybrid scaffold for bone
                                                                      regeneration
                                                                      A Tampieri, E Landi, F Valentini, M Sandri, T D’Alessandro, V Dediu and M Marcacci


                                                                      2011 Nanotechnology 22 015104

                                                                      Magnetic bio-hybrid porous scaffolds have been synthesized, nucleating nano-apatite in situ on self-
                                                                      assembling collagen, in the presence of magnetite nano-particles. The magnetic phase acted as a sort
                                                                      of cross-linking agent for the collagen, inducing a chemico-physical-mechanical stabilization of the
                                                                      material and allowing us to control the porosity network of the scaffold. Gradients of bio-mineralization
                                                                      and magnetization were also developed for osteochondral application. The good potentiality of the
ESEM image showing a non-cross linked magnetic hydroxyapatite/
                                                                      material as a biomedical device, able to offer assistance to bone regeneration through scaffold
collagen composite.                                                   reloading with specific factors guided by an external magnetic field, has been preliminarily investigated.
                                                                      Up to now the proof of this concept has been realized through in vitro assessments.



                                                                      Surface functionalization of PLGA nanoparticles by
                                                                      non-covalent insertion of a homo-bifunctional spacer for
                                                                      active targeting in cancer therapy
                                                                      S I Thamake, S L Raut, A P Ranjan, Z Gryczynski and J K Vishwanatha


                                                                      2011 Nanotechnology 22 035101

                                                                      This work reports the surface functionalization of polymeric PLGA nanoparticles by non-covalent
                                                                      insertion of a homo-bifunctional chemical crosslinker, bis(sulfosuccinimidyl) suberate (BS3)
                                                                      for targeted cancer therapy. We dissolved BS3 in aqueous solution of PVA during formulation of
                                                                      nanoparticles by a modified solid/oil/water emulsion solvent evaporation method. The non-covalent
                                                                      insertion of BS3 was confirmed by Fourier transform infrared (FTIR) spectroscopy. Curcumin and
                                                                      annexin A2 were used as a model drug and a cell specific target, respectively. Nanoparticles were
Confocal microscopy image of antibody coated PLGA nanoparticles.
                                                                      characterized for particle size, zeta potential and surface morphology. The qualitative assessment of
In this instance the PLGA nanoparticles are first covered with Nile   antibody attachment was performed by transmission electron microscopy (TEM) as well as confocal
red stained particles and then coated with alexa 488 conjugated       microscopy. The optimized formulation showed antibody attachment of 86%. However, antibody
antibodies.                                                           attachment was abolished upon blocking the functional groups of BS3. The availability of functional
                                                                      antibodies was evaluated by the presence of a light chain fraction after gel electrophoresis. We further
                                                                      evaluated the in vitro release kinetics of curcumin from antibody coated and uncoated nanoparticles.
                                                                      The release of curcumin is enhanced upon antibody attachment and followed an anomalous release
                                                                      pattern. We also observed that the cellular uptake of nanoparticles was significantly higher in annexin
                                                                      A2 positive cells than in negative cells. Therefore, these results demonstrate the potential use of this
                                                                      method for functionalization as well as to deliver chemotherapeutic agents for treating cancer.




                                                                      Amphiphilic polymer-coated hybrid nanoparticles as
                                                                      CT/MRI dual contrast agents
                                                                      Dongkyu Kim, Mi Kyung Yu, Tae Sup Lee, Jae Jun Park, Yong Yeon Jeong and Sangyong Jon


                                                                      2011 Nanotechnology 22 155101

                                                                      We describe hybrid nanoparticles, composed of iron oxide and gold nanoparticles, as potential dual
                                                                      contrast agents for both computed tomography (CT) and magnetic resonance imaging (MRI). The hybrid
                                                                      nanoparticles are synthesized by thermal decomposition of mixtures of Fe-oleate and Au-oleylamine
                                                                      complexes. Using a nano-emulsion method, the nanoparticles are coated with amphiphilic poly(DMA-r-
                                                                      mPEGMA-r-MA) to impart water-dispersity and antibiofouling properties. An in vitro phantom study shows
TEM image of hybrid Au–Fe 3O4 nanoparticles after coating with
                                                                      that the hybrid nanoparticles have high CT attenuation, because of the constituent gold nanoparticles,
poly(DMA-r -mPEGMA-r-MA). The scale bar indicated 20nm.               and afford a good MR signal, attributable to the contained iron oxide nanoparticles. Intravenous injection
                                                                      of the hybrid nanoparticles into hepatoma-bearing mice results in high contrast between the hepatoma
                                                                      and normal hepatic parenchyma in both CT and MRI. These results suggest that the hybrid nanoparticles
                                                                      may be useful as CT/MRI dual contrast agents for in vivo hepatoma imaging.

                                                                                                                                                               Nanotechnology    9
Nanotechnology Highlights 2011




                                                                      Control of neuronal network organization by




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                                                                                                                                                              Fe tec
                                                                                                                                                                no
                                                                      chemical surface functionalization of multi-




                                                                                                                                                                 at hw
                                                                                                                                                                   ur e
                                                                                                                                                                     ed b
                                                                      walled carbon nanotube arrays




                                                                                                                                                                       on .org
                                                                      Jie Liu, Florence Appaix, Olivier Bibari, Gilles Marchand, Alim-Louis Benabid, Fabien Sauter-Starace
                                                                      and Michel De Waard


                                                                      2011 Nanotechnology 22 195101

                                                                      Carbon nanotube substrates are promising candidates for biological applications and devices. Interfacing
                                                                      of these carbon nanotubes with neurons can be controlled by chemical modifications. In this study, we
                                                                      investigated how chemical surface functionalization of multi-walled carbon nanotube arrays (MWNT-A)
                                                                      influences neuronal adhesion and network organization. Functionalization of MWNT-A dramatically
Confocal microscopy image of neuronal cluster illustrating cluster-   modifies the length of neurite fascicles, cluster inter-connection success rate, and the percentage of
emerging neurite organisation. The green areas show Alexa488
                                                                      neurites that escape from the clusters. We propose that chemical functionalization represents a method
labelling and the red, To-Pro3 staining.
                                                                      of choice for developing applications in which neuronal patterning on MWNT-A substrates is required.



                                                                      A novel cationic liposome formulation for efficient gene
                                                                      delivery via a pulmonary route
                                                                      Peng Li, Donghua Liu, Xiaoli Sun, Chunxi Liu, Yongjun Liu and Na Zhang


                                                                      2011 Nanotechnology 22 245104

                                                                      The clinical success of gene therapy for lung cancer is not only dependent on efficient gene carriers
                                                                      but also on a suitable delivery route. A pulmonary delivery route can directly deliver gene vectors to
                                                                      the lung which is more efficient than a systemic delivery route. For gene carriers, cationic liposomes
                                                                      have recently emerged as leading non-viral vectors in worldwide gene therapy clinical trials. However,
                                                                      cytotoxic effects or apoptosis are often observed which is mostly dependent on the cationic lipid
Fluorescent image of cells in bronchoalveolar lavage fluids
                                                                      used. Therefore, an efficient and safe cationic lipid, 6-lauroxyhexyl lysinate (LHLN), previously
transfected with Lipofectamine/DNA and LHLN-liposome/DNA
complexes. The gene expression was examined 48 hours post-            synthesized by our group was first used to prepare cationic liposomes. Physicochemical and
transfection.                                                         biological properties of LHLN-liposomes were investigated. LHLN-liposome/DNA complexes showed
                                                                      positive surface charge, spherical morphology, a relatively narrow particle size distribution and strong
                                                                      DNA binding capability. Compared with Lipofectamine2000, the new cationic liposome formulation
                                                                      using LHLN exhibited not only lower cytotoxicity (P < 0.05) but also similar transfection efficiency in
                                                                      A549 and HepG2 lung cancer cells for in vitro tests. When administered by intratracheal instillation
                                                                      into rat lungs for in vivo evaluation, LHLN-liposome/DNA complexes exhibited higher pulmonary gene
                                                                      transfection efficiency than Lipofectamine2000/DNA complexes (P < 0.05). These results suggested
                                                                      that LHLN-liposomes may have great potential for efficient pulmonary gene delivery.



                                                                      Depth-sensing nano-indentation on a myelinated axon at
                                                                      various stages
                                                                      Wei-Chin Huang, Jiunn-Der Liao, Chou-Ching K Lin and Ming-Shaung Ju


                                                                      2011 Nanotechnology 22 275101

                                                                      A nano-mechanical characterization of a multi-layered myelin sheath structure, which enfolds
                                                                      an axon and plays a critical role in the transmission of nerve impulses, is conducted. Schwann
                                                                      cells co-cultured in vitro with PC12 cells for various co-culture times are differentiated to form a
                                                                      myelinated axon, which is then observed using a transmission electron microscope. Three major
                                                                      myelination stages, with distinct structural characteristics and thicknesses around the axon, can
TEM image of a fixed axon after co-culture for 17 days. The blue
                                                                      be produced by varying the co-culture time. A dynamic contact module and continuous depth-
arrow indicates Myelin while the red arrow shows the periaxonal
space. This image shows the multi-layer structure of M-II; the        sensing nano-indentation are used on the myelinated structure to obtain the load-on-sample versus
myelination process results in a dense outermost layer and an inner   measured displacement curve of a multi-layered myelin sheath, which is used to determine the work
periaxonal space structure. Scale bar is 1 μm.                        required for the nano-indentation tip to penetrate the myelin sheath. By analyzing the harmonic
                                                                      contact stiffness versus the measured displacement profile, the results can be used to estimate the
                                                                      three stages of the multi-layered structure on a myelinated axon. The method can also be used to
                                                                      evaluate the development stages of myelination or demyelination during nerve regeneration.
10    Nanotechnology
                                                                                                  Nanotechnology Highlights 2011




Electronics and photonics
  Sponsored by           AIXTRON manufactures turn-key deposition systems for graphene, carbon nanotubes and
                         semiconducting nanowires using chemical vapor deposition (CVD) and plasma enhanced
                         chemical vapor deposition (PECVD). These tools have a proven track record and cover 2”
                         to 12” wafer-scale production. Also see the Materials: synthesis or self assembly category
                         on p24. Visit www.aixtron.com.


Electronics is arguably the industry with the most              can be rotated by applying a few millivolts, and solve
consumer awareness of nanotechnology. From music                the Landau–Lifshitz–Gilbert (LLG) equation to find the
players for disco divas to sattelite navigation for             switching delays in the associated bit flips and clock rate.
hikers, there are few functions that people would not
expect to have available on their smart phone. These            Resistive switching nanostructures are providing new
increasingly sophisticated devices have been facilitated        non-volatile memory architectures. In May 2011 we
by developments in a broad range of fields in nanoscale         published a special issue dedicated to the latest
electronics and photonics.                                      cutting-edge developments in the field. Among the
                                                                work published was a paper by researchers at HP Labs
There’s good news for touch screen users as researchers         in the US that provided insights into the mechanism
in the US demonstrate a simple spray deposition                 behind the resistive switching TiO2-based devices. More
technique for fabricating a Ag nanowire thin film that can      recently, researchers in Germany have devised a new
be used as a transparent conducting electrode. The film         measurement approach that gets around the destructive
is cheap and easy to fabricate and production may be            read-out of current-based methods, easing material
scaled up to large areas. In addition, the conductivity of      endurance requirements while providing a more energy
the film was better than other examples based on carbon         efficient solution.
nanotubes and graphene.
                                                                Advances in electronics are pushing at the boundaries
Energy efficiency is an increasingly important factor as        in all directions, with a resulting rate of technological
devices are scaled down in size. Nanomagnets present            developments that is awesome to both researchers and
the potential to improve the efficiency of logic gates.         consumers alike. Be it on your PC, smart phone or a free
Supriyo Bandyopadhyay and researchers at Virginia               sample hard copy, there’s a wealth of fascinating new
Commonwealth University in the US consider how the              developments to browse in the electronics and photonics
magnetization of a nanomagnet in a piezoelectric layer          section of this year’s Nanotechnology highlights.



                         Section scope
                         Nanoscale materials and systems are an increasingly integral feature of advances in electronics
                         and photonics device technology. Shrinking device footprints and novel optical device elements
                         have transformed the products available to consumers and industry, as well as catalysing rapid
                         progress in our understanding of the fundamental physics at the heart of nanoscale systems.
                         This section is dedicated to research into new and improved electronic and photonic devices
 Section Editor: Meyya   and the advances in our understanding of nanostructure properties that fuel the progress. Only
 Meyyappan               reports describing a clear and significant advance in the field may be considered for publication
                         as a regular paper. Research published in the section deals with a number of fields including
 plasmonics, non-volatile memory devices, LEDs, understanding and manipulating fluorescence, novel photonic
 sources and detectors, the interaction of low-dimensional systems with light and electric fields and the potential for
 optoelectronic interfacing, as well as the physics that underlines these systems, and much more.


                                                                                                               Nanotechnology   11
Nanotechnology Highlights 2011




                                                                      Improved conversion efficiency of CdS quantum
                                                                      dots-sensitized TiO2 nanotube array using ZnO energy
                                                                      barrier layer
                                                                      Chong Chen, Yi Xie, Ghafar Ali, SeungHwa Yoo and SungOh Cho


                                                                      2011 Nanotechnology 22 015202

                                                                      We report that the use of a chemically deposited ZnO energy barrier between a CdS quantum
                                                                      dot sensitizer and TiO2 nanotubes (TNTs) can improve the efficiency of quantum dots-sensitized
                                                                      solar cells (QDSCs). The experimental results show that the formation of the ZnO layers over TNTs
                                                                      significantly improved the performances of the CdS QDSCs based on the TNTs electrodes. In
                                                                      particular, a maximum photoconversion efficiency of 4.6% was achieved for the CdS/ZnO/TNTs
                                                                      electrode under UV–visible light illumination, corresponding to an increase of 43.7% as compared
Top view SEM image of a CdS(10)/ZnO/TNTs film showing that a          to the CdS/TNTs electrode without the ZnO layers. The improved CdS QDSCs efficiency is attributed
well-ordered pore structure exists.
                                                                      to the suppressed recombination of photoinjected electrons with redox ions from the electrolyte
                                                                      resulting from the ZnO energy barrier layers.




                                                                      Combined micro- and nano-scale surface




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                                                                      textures for enhanced near-infrared light




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                                                                      harvesting in silicon photovoltaics




                                                                                                                                                                        on .org
                                                                      Chia-Hua Chang, Peichen Yu, Min-Hsiang Hsu, Ping-Cheng Tseng, Wei-Lun Chang,Wen-Ching Sun,
                                                                      Wei-Chih Hsu, Shih-Hsin Hsu and Yia-Chung Chang


                                                                      2011 Nanotechnology 22 095201

                                                                      As silicon photovoltaics evolve towards thin-wafer technologies, efficient optical absorption for the
                                                                      near-infrared wavelengths has become particularly challenging. In this work, we present a solution
                                                                      that employs combined micro- and nano-scale surface textures to increase light harvesting in the
                                                                      near-infrared for crystalline silicon photovoltaics, and discuss the associated antireflection and
A titled top view scanning electron micrographs of indium-tin-oxide
                                                                      scattering mechanisms. The surface textures are achieved by uniformly depositing a layer of indium-
nanowhiskers deposited on a passivated, micro-grooved silicon
solar cell. The scalar bars are 4 μm in length.                       tin-oxide nanowhiskers on micro-grooved silicon substrates using electron-beam evaporation.
                                                                      The nanowhiskers facilitate optical transmission in the near-infrared by functioning as impedance
                                                                      matching layers with effective refractive indices gradually varying from 1 to 1.3. Materials with such
                                                                      unique refractive index characteristics are not readily available in nature. As a result, the solar cell with
                                                                      combined textures achieves over 90% external quantum efficiencies for a broad wavelength range of
                                                                      460–980 nm, which is crucial to the development of advanced thin-substrate silicon solar cells.




                                            “This is absolutely terrific, thank you very much for promoting our work on
                                            nanotechweb.org.”
                                            Stefan Harrer IBM Research Division, TJ Watson Research Center
                                            (e-mail sharrer@us.ibm.com)

                                            • Passivated nanopores withstand extreme voltages
                                               http://nanotechweb.org/cws/article/lab/46476




12    Nanotechnology
                                                                                                                                  Nanotechnology Highlights 2011




                                                             Magnetization dynamics, Bennett clocking and associated
                                                             energy dissipation in multiferroic logic
                                                             Mohammad Salehi Fashami, Kuntal Roy, Jayasimha Atulasimha and Supriyo Bandyopadhyay


                                                             2011 Nanotechnology 22 155201

                                                             It has been recently shown that the magnetization of a multiferroic nanomagnet, consisting of
                                                             a magnetostrictive layer elastically coupled to a piezoelectric layer, can be rotated by a large
                                                             angle if a tiny voltage of a few tens of millivolts is applied to the piezoelectric layer. The potential
                                                             generates stress in the magnetostrictive layer and rotates its magnetization by ∼90° to implement
                                                             Bennett clocking in nanomagnetic logic chains. Because of the small voltage needed, this
Three-dimensional plot of magnetization components of a
                                                             clocking method is far more energy efficient than those that would employ spin transfer torque or
nanomagnet showing the spatial excursion of the tip of the
magnetization vector.                                        magnetic fields to rotate the magnetization. In order to assess if such a clocking scheme can also
                                                             be reasonably fast, we have studied the magnetization dynamics of a multiferroic logic chain with
                                                             nearest-neighbor dipole coupling using the Landau–Lifshitz–Gilbert (LLG) equation. We find that
                                                             clock rates of 2.5 GHz are feasible while still maintaining the exceptionally high energy efficiency.
                                                             For this clock rate, the energy dissipated per clock cycle per bit flip is ∼52 000 kT at room
                                                             temperature in the clocking circuit for properly designed nanomagnets. Had we used spin transfer
                                                             torque to clock at the same rate, the energy dissipated per clock cycle per bit flip would have been
                                                             ∼4 × 108 kT, while with current transistor technology we would have expended ∼106 kT. For slower
                                                             clock rates of 1 GHz, stress-based clocking will dissipate only ∼200 kT of energy per clock cycle
                                                             per bit flip, while spin transfer torque would dissipate about 108 kT. This shows that multiferroic
                                                             nanomagnetic logic, clocked with voltage-generated stress, can emerge as a very attractive
                                                             technique for computing and signal processing since it can be several orders of magnitude more
                                                             energy efficient than current technologies.




                                                             Large scale, highly conductive and patterned




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                                                             transparent films of silver nanowires on



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                                                             arbitrary substrates and their application in touch




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                                                             screens
                                                             Anuj R Madaria, Akshay Kumar and Chongwu Zhou


                                                             2011 Nanotechnology 22 245201

                                                             The application of silver nanowire films as transparent conductive electrodes has shown promising
                                                             results recently. In this paper, we demonstrate the application of a simple spray coating technique
                                                             to obtain large scale, highly uniform and conductive silver nanowire films on arbitrary substrates.
SEM image of the Ag nanowire network, showing nanowire
                                                             We also integrated a polydimethylsiloxane (PDMS)-assisted contact transfer technique with spray
distribution on an individual fiber.                         coating, which allowed us to obtain large scale high quality patterned films of silver nanowires. The
                                                             transparency and conductivity of the films was controlled by the volume of the dispersion used in
                                                             spraying and the substrate area. We note that the optoelectrical property, σDC/σOp, for various films
                                                             fabricated was in the range 75–350, which is extremely high for transparent thin film compared to
                                                             other candidate alternatives to doped metal oxide film. Using this method, we obtain silver nanowire
                                                             films on a flexible polyethylene terephthalate (PET) substrate with a transparency of 85% and sheet
                                                             resistance of 33 Ω/sq, which is comparable to that of tin-doped indium oxide (ITO) on flexible
                                                             substrates. In-depth analysis of the film shows a high performance using another commonly used
                                                             figure-of-merit, ΦTE. Also, Ag nanowire film/PET shows good mechanical flexibility and the application
                                                             of such a conductive silver nanowire film as an electrode in a touch panel has been demonstrated.




                                                                                                                                                  Nanotechnology   13
Nanotechnology Highlights 2011




                                                                      Optical properties of quantum-dot-decorated polymer
                                                                      nanofibers
                                                                      Huaqing Yu, Rui Zhang and Baojun Li


                                                                      2011 Nanotechnology 22 335202

                                                                      We report a one-step process for decorating poly(trimethylene terephthalate) (PTT) nanofibers with
                                                                      CdSe/ZnS core/shell quantum dots (QDs). Using the QD-decorated PTT nanofibers with diameters
Optical microscope image of the quantum dot-decorated nanofiber       of 400–800 nm as active subwavelength waveguides, their high photostability for 630 nm red
with diameter of 490 nm excited by a 473 nm laser. The blue arrow     light and low absorption coefficient down to 2.6 cm−1 were characterized by both evanescent
shows the direction of propagation of the launched light.             waveguiding excitation and irradiation excitation. Compared with the irradiation excitation, a 200
                                                                      times enhancement was obtained from the active subwavelength waveguides under the evanescent
                                                                      waveguiding excitation.




                                                                      Capacity based nondestructive readout for complementary
                                                                      resistive switches
                                                                      S Tappertzhofen, E Linn, L Nielen, R Rosezin, F Lentz, R Bruchhaus, I Valov, U Böttger and R Waser


                                                                      2011 Nanotechnology 22 395203

                                                                      Complementary resistive switches (CRS) were recently suggested to solve the sneak path
                                                                      problem of larger passive memory arrays. CRS cells consist of an antiserial setup of two bipolar
                                                                      resistive switching cells. The conventional destructive readout for CRS cells is based on a current
                                                                      measurement which makes a considerable call on the switching endurance. Here, we report a new
Output voltage Vout for short pulse lengths (50 ns) applied to SiO2   approach for a nondestructive readout (NDRO) based on a capacity measurement. We suggest
cells and pulse heights of Vin = 2 V and Vin = 3 V, respectively.     a concept of an alternative setup of a CRS cell in which both resistive switching cells have similar
Voltage margins are about 46 mV for the 2 V input pulse and 68 mV     switching properties but are distinguishable by different capacities. The new approach has the
for 3 V input.                                                        potential of an energy saving and fast readout procedure without decreasing cycling performance
                                                                      and is not limited by the switching kinetics for integrated passive memory arrays.




14    Nanotechnology
                                                                                               Nanotechnology Highlights 2011




Energy at the nanoscale
The new energy section in Nanotechnology was                   Hydrogen storage also has huge potential in the energy
launched in 2011. We introduced this section to the            industry. Among the top research papers in this area is a
journal in recognition of the important role of nanoscale      report by Yue Chan and James M Hill at the University of
science and technology in this fast growing field of           Adelaide in Australia. They have numerically investigated
research. Papers in the section include work to refine         the optimum structures for a graphene oxide framework
and develop new technology for generating and storing          supported by benzenediboronic pillars for maximum
energy. The section also contains work that looks into         hydrogen storage.
fundamental processes in energy conservation and
transfer, such as the localization of energy dissipation.      Carbon-based nanostructures also feature in the work on
                                                               improving the performance of supercapacitors, reported
Photovoltaics is one of the fields that command the            by researchers at Florida State University. They develop
greatest activity in alternative energy research. Organic-     a composite material of vanadium oxide and multiwall
based devices now offer a low-cost alternative to              carbon nanotube buckypaper that has excellent
traditional silicon solar cells. Over the year the section     supercapacitor performance and offers a cost-effective
has published a number of high-quality reports focused         alternative to other transition metal oxides.
on improving the efficiencies of these devices to make
them commercially viable. As highlighted in this brochure,     Research into storing and generating energy deals with
Thomas Tromholt and colleagues in Denmark and Israel           concerns that are equally prevalent in both the general
have complemented this work with an investigation into         press and academic literature. This section gives
the longevity of solar cells, an aspect that has received      some indication of how much fascinating science and
far less study so far. The report provides insights into the   innovation these concerns have inspired.
validity of data after exposure to concentrated sunlight as
a means of accelerating studies of device degradation.




                         Section scope
                           Nanoscale science and technology research forms a fundamental component in the
                           development of alternative energy sources. In view of mounting awareness of the current
                           limitations of the world’s energy resources, research in this field is becoming increasingly
                           important. The new section in Nanotechnology focuses on innovative techniques based
                           on nanostructures that can be applied towards all forms of energy generation and storage,
                           and embraces both advances in the fundamental science involved as well as technological
                           innovations. Papers published in the new section describe ways to improve the efficiency,
 Section Editor: John Vajo stability and processibility of photovoltaic devices, hydrogen storage units, fuel cells,
                           and a range of other energy-related fields of research. The reports cover work towards the
 development of sophisticated new nanomaterials and fabrication techniques, as well as studies that aim to deepen
 our understanding of the fundamental mechanisms at work in the latest energy generating and storing devices.




                                                                                                            Nanotechnology   15
Nanotechnology Highlights 2011




                                                                      Reversible degradation of inverted organic solar cells by
                                                                      concentrated sunlight
                                                                      Thomas Tromholt, Assaf Manor, Eugene A Katz and Frederik C Krebs


                                                                      2011 Nanotechnology 22 225401

                                                                      Concentrated sunlight was used to study the performance response of inverted P3HT:PCBM organic
                                                                      solar cells after exposure to high intensity sunlight. Correlations of efficiency as a function of solar
                                                                      intensity were established in the range of 0.5–15 suns at three different stages: for a pristine cell, after
                                                                      30 min exposure at 5 suns and after 30 min of rest in the dark. High intensity exposure introduced
                                                                      a major performance decrease for all solar intensities, followed by a partial recovery of the lost
A plot showing the evolution of the efficiency of the cell. The
                                                                      performance over time: at 1 sun only 6% of the initial performance was conserved after the high
black plot refers to a pristine cell, the red immediately following   intensity exposure, while after rest the performance had recovered to 60% of the initial value. The
degradation and the blue following a rest period.                     timescale of the recovery effect was studied by monitoring the cell performance at 1 sun after high
                                                                      intensity exposure. This showed that cell performance was almost completely restored after 180 min.
                                                                      The transient state is believed to be a result of the breakdown of the diode behaviour of the ZnO electron
                                                                      transport layer by O2 desorption, increasing the hole conductivity. These results imply that accelerated
                                                                      degradation of organic solar cells by concentrated sunlight is not a straightforward process, and care
                                                                      has to be taken to allow for a sound accelerated lifetime assessment based on concentrated sunlight.




                                                                      Obviating the requirement for oxygen in SnO2-based
                                                                      solid-state dye-sensitized solar cells
                                                                      Pablo Docampo and Henry J Snaith


                                                                      2011 Nanotechnology 22 225403

                                                                      Organic semiconductors employed in solar cells are perfectly stable to solar irradiation provided
                                                                      oxygen content can be kept below 1 ppm. Paradoxically, the state-of-the-art molecular hole-
                                                                      transporter-based solid-state dye-sensitized solar cells only operate efficiently if measured in
                                                                      an atmosphere containing oxygen. Without oxygen, these devices rapidly lose photovoltage
                                                                      and photocurrent and are rendered useless. Clearly this peculiar requirement has detrimental
                                                                      implications to the long term stability of these devices. Through characterizing the solar cells in air
                                                                      and in oxygen-free atmospheres, and considering the device architecture, we identify that direct
Schematic illustration of a SnO2-based solid-state dye-sensitized
solar cell with the addition of a mesoporous interlayer of Al2O3 on
                                                                      contact between the metallic cathode and the mesoporous metal oxide photo-anode is responsible
top of the mesoporous SnO2.                                           for a shunting path through the device. This metal–metal oxide contact forms a Schottky barrier
                                                                      under ambient conditions and the barrier is suitably high so as to prevent significant shunting of
                                                                      the solar cells. However, under light absorption in an anaerobic atmosphere the barrier reduces
                                                                      significantly, opening a low resistance shunting path which dominates the current–voltage
                                                                      characteristics in the solar cell. By incorporating an extra interlayer of insulating mesoporous
                                                                      aluminum oxide, on top of the mesoporous semiconducting metal oxide electrode, we successfully
                                                                      block this shunting path and subsequently the devices operate efficiently in an oxygen-free
                                                                      atmosphere, enabling the possibility of long term stability of solid-state dye-sensitized solar cells.




                                                                      Nanosilicon in water as a source of hydrogen: size and pH
                                                                      matter
                                                                      Bernhard Goller, Dmitry Kovalev and Olga Sreseli


                                                                      2011 Nanotechnology 22 305402

                                                                      We report on the interaction of silicon nanocrystals with water/alcohol solutions which results in their
                                                                      complete oxidation, the hydrolysis of water and hydrogen generation in amounts close to the ideal
                                                                      scenario. Water acts as an oxidizer while alcohol is required for efficient wetting of nanosilicon. This
TEM image showing freestanding Si nanospheres prepared from the       process results in the formation of silicon-based alcogel which can be further transferred to aerogel.
gas phase and subsequently stain etched.




16     Nanotechnology
                                                                                                                                             Nanotechnology Highlights 2011




                                                                        Hydrogen storage inside graphene-oxide frameworks
                                                                        Yue Chan and James M Hill


                                                                        2011 Nanotechnology 22 305403

                                                                        In this paper, we use applied mathematical modelling to investigate the storage of hydrogen
                                                                        molecules inside graphene-oxide frameworks, which comprise two parallel graphenes rigidly
                                                                        separated by perpendicular ligands. Hydrogen uptake is calculated for graphene-oxide frameworks
                                                                        using the continuous approximation and an equation of state for both the bulk and adsorption
                                                                        gas phases. We first validate our approach by obtaining results for two parallel graphene sheets.
                                                                        This result agrees well with an existing theoretical result, namely 1.85 wt% from our calculations,
The total potential energy for hydrogen stored between two parallel
graphene sheets G-120 with D = 11 A° , where E is in eV and h and       and 2 wt% arising from an ab initio and grand canonical Monte Carlo calculation. This provides
r are in A° .                                                           confidence to the determination of the hydrogen uptake for the four graphene-oxide frameworks,
                                                                        GOF-120, GOF-66, GOF-28 and GOF-6, and we obtain 1.68, 2, 6.33 and 0 wt%, respectively. The
                                                                        high value obtained for GOF-28 may be partly explained by the fact that the benzenediboronic acid
                                                                        pillars between graphene sheets not only provide mechanical support and porous spaces for the
                                                                        molecular structure but also provide the higher binding energy to enhance the hydrogen storage
                                                                        inside graphene-oxide frameworks. For the other three structures, this binding energy is not as large
                                                                        in comparison to that of GOF-28 and this effect diminishes as the ligand density decreases. In the
                                                                        absence of conflicting data, the present work indicates GOF-28 as a likely contender for practical
                                                                        hydrogen storage.




                                                                        How localized are energy dissipation




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                                                                        processes in nanoscale interactions?




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                                                                        Sergio Santos, Victor Barcons, Albert Verdaguer, Josep Font, Neil H Thomson and Matteo Chiesa


                                                                        2011 Nanotechnology 22 345401

                                                                        We describe fundamental energy dissipation in dynamic nanoscale processes in terms of the
                                                                        localization of the interactions. In this respect, the areal density of the energy dissipated per cycle
                                                                        and the effective area of interaction in which each process occurs are calculated for four elementary
                                                                        dissipative processes. It is the ratio between these two, which we term M, that provides information
Scheme of the non-contact interaction area Snc for a tip in the         about how localized the interactions are. While our results are general, we use concepts from
proximity of a surface for the long range attractive forces (d > a0).
                                                                        dynamic atomic force microscopy to describe the physical phenomenon. We show that neither
The tip radius is termed R. The gradient shows how the effective
radius rnc grows as larger fractions p of the interaction are           the phase lag, nor the magnitude of the energy dissipated alone provide information about how
considered. This radius, and area, are thus termed rnc(p) and Snc(p)    dissipative processes are localized. Instead, M has to be considered.
respectively.




                                                                        Supercritical fluid deposition of vanadium oxide on
                                                                        multi-walled carbon nanotube (MWCNT) buckypaper for
                                                                        supercapacitor electrode application
                                                                        Quyet Huu Do, Changchun Zeng, Chuck Zhang, Ben Wang and Jim Zheng


                                                                        2011 Nanotechnology 22 365402

                                                                        Composite electrodes were fabricated for supercapacitor application, by depositing vanadium oxide
                                                                        onto multi-walled carbon nanotubes (MWCNTs) buckypaper using supercritical fluid deposition
SEM micrograph showing a cross-section of a vanadium oxide –
                                                                        (SFD). The deposited thin vanadium oxide layer showed amorphous structure with excellent
buckypaper composite. The top of the image corresponds to the           uniformity. In aqueous KCl electrolyte, the vanadium oxide exhibited a constant pseudo-capacitance
centre the sample and the bottom of the image the sample surface.       of ~1024 F g–1, which was independent of the oxide material loading (up to 6.92 wt%) and voltage
                                                                        scan rate (up to 100 mV s–1).The highest specific electrode capacitance achieved was ~85 F g–1,
                                                                        which was almost four times that of the pristine buckypaper electrode.




                                                                                                                                                             Nanotechnology   17
Nanotechnology Highlights 2011




Patterning and nanofabrication
  Sponsored by                   The Orion Plus is powered by the revolutionary atomic-sized, ALIS gas field ion source.
                                 This helium ion microscope offers high depth of field with high-resolution surface imaging,
                                 superior charge control for easy imaging of insulating samples without conductive
                                 coating, etch and deposition for 3D nanofabrication, backscatter ion spectroscopy and
                                 thin film analytics. Visit www.zeiss.com/nts to learn more or send an e-mail to
                                 info-usa@nts.zeiss.com.



Patterns have fascinated for millennia. In ancient times,            use a process consisting of high-resolution electron-
the study of patterns in numbers and nature gave rise                beam lithography followed directly by magnetic film
to the disciplines of maths and physics. Applying these              deposition. The simplicity of the process allows greater
disciplines allowed the design of devices and machinery              pattern resolution.
that have evolved into the sophisticated technology that
supports modern day life. Now research in nanoscale                  The properties of patterned surfaces also have a
fabrication uses advances in technology to create                    role to play in applications for fighting flu. In Taiwan,
carefully defined patterns and features that lend tailored           researchers have optimized gold nano/microstructures
properties to materials for optimized device design. The             with controlled geometrical parameters for surface
section on patterning and nanofabrication in this year’s             enhanced Raman spectroscopy (SERS) detection of
Nanotechnology highlights brochure underlines just how               R6G molecules and the flu virus. Their observations
rapidly progress in the field is being made.                         suggest that the distance between micro/nanostructures
                                                                     was the dominant factor in SERS detection.
At New York University researchers have studied the
interference patterns that arise from propagating spin               New limits are constantly being defined and overcome
waves. They show how the patterns can be used for                    through research in nanofabrication. The mathematician
polychronous wave computation, a concept inspired by                 and philosopher Alfred North Whitehead is quoted as
studies of the brain. The spin-wave interference patterns            having said: “art is the imposing of a pattern on experience,
introduce possibilities for computation and data storage.            and our aesthetic enjoyment is recognition of the pattern”.
                                                                     Perhaps certain aspects of nanotechnology can be
Researchers in Singapore tackle the pattern resolution               described as the imposing of experience on patterns, so
limitations of producing bit-patterned media at data                 that technological advances allow increasing control and
concentrations beyond 1.5 Tbit per square inch. They                 design in the resulting properties of nanomaterials.



                             Section scope
                         As device sizes approach the nanoscale the effects from various fundamental forces, which
                         are neglected at the macroscale, are dominant. In order to explore and utilize these unique
                         conditions it is a continual goal of nanoscientists to improve methods of accurately fabricating
                         devices and patterning surfaces at the nanoscale. This section focuses on comprehensive
                         presentations of novel methods to increase the resolution, control and efficiency of nanoscale
 Section Editor: Sergei  production and demonstrate new applications based on these nanofabricated materials. A
 Kalinin                 wide range of lithography techniques are covered in this section including both bottom-up and
                         top-down methods. We emphasise the need for articles to demonstrate real improvements
 in techniques by direct comparison with other methods. These improvements can take many forms. For example,
 demonstrating improvement in the control of a technique, increasing the area or conditions in which the technique can
 be performed, increasing speed or output of the technique or of reducing cost of fabrication.


18   Nanotechnology
                                                                                                                                             Nanotechnology Highlights 2011




                                                                       Nanoimprinting lithography of a two-layer phase mask
                                                                       for three-dimensional photonic structure holographic
                                                                       fabrications via single exposure
                                                                       Di Xu, Kevin P Chen, Kris Ohlinger and Yuankun Lin


                                                                       2011 Nanotechnology 22 035303

                                                                       We report a combined holographic and nanoimprinting lithography technique to produce three-
                                                                       dimensional woodpile photonic crystal templates through only one single exposure. The interference
                                                                       lithography process uses an integratable diffractive optical element for large throughput 3D
                                                                       pattern manufacturing. The diffractive optical element consists of two layers of phase grating
                                                                       separated by an intermediate layer, fabricated by repeated nanoimprinting lithography, followed
                                                                       by an SU8 photoresist bonding technique. Grating periods, relative orientation, diffraction angle,
                                                                       and efficiency, as well as layer to layer phase delay, are well designed during manufacturing. By
SEM image of structure in a photoresist with face centre tetragonal
(FCT) symmetry fabricated by a single laser exposure through           thermally optimizing the thickness of the intermediate layer, this paper demonstrates the fabrication
an orthogonal two-layer phase mask. The inset is the simulated         of interconnected 3D photonic structures with arbitrary symmetry through a single laser exposure.
structure for comparison.                                              The two-layer phase mask approach enables a CMOS-compatible monolithic integration of 3D
                                                                       photonic structures with other integrated optical elements and waveguides.




                                                                       Fabrication and characterization of bit-patterned media
                                                                       beyond 1.5 Tbit/in2
                                                                       Joel K W Yang, Yunjie Chen, Tianli Huang, Huigao Duan, Naganivetha Thiyagarajah, Hui Kim Hui,
                                                                       Siang Huei Leong and Vivian Ng


                                                                       2011 Nanotechnology 22 385301

                                                                       We fabricated bit-patterned media (BPM) at densities as high as 3.3 Tbit/in2 using a process
                                                                       consisting of high-resolution electron-beam lithography followed directly by magnetic film deposition.
                                                                       By avoiding pattern transfer processes such as etching and liftoff that inherently reduce pattern
                                                                       fidelity, the resolution of the final pattern was kept close to that of the lithographic step. Magnetic
SEM images of magnetic bits after Co/Pd multilayer film deposition     force microscopy (MFM) showed magnetic isolation of the patterned bits at 1.9 Tbit/in2, which was
onto pre-patterned hydrogen silsesquioxane (HSQ) posts. The            close to the resolution limit of the MFM. The method presented will enable studies on magnetic bits
dashed line illustrates the side profile of an isolated bit.
                                                                       packed at ultra-high densities, and can be combined with other scalable patterning methods such as
                                                                       templated self-assembly and nanoimprint lithography for high-volume manufacturing.




                                                                       Spin-wave interference patterns created by
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                                                                       spin-torque nano-oscillators for memory and
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                                                                       Ferran Macià, Andrew D Kent and Frank C Hoppensteadt


                                                                       2011 Nanotechnology 22 095301

                                                                       Magnetization dynamics in nanomagnets has attracted broad interest since it was predicted that a dc
                                                                       current flowing through a thin magnetic layer can create spin-wave excitations. These excitations are
                                                                       due to spin momentum transfer, a transfer of spin angular momentum between conduction electrons
                                                                       and the background magnetization, that enables new types of information processing. Here we show
A simulation of the magnetic excitations formed by three point
contacts on a two-dimensional thin film. The magnetic excitations
                                                                       how arrays of spin-torque nano-oscillators can create propagating spin-wave interference patterns
diffuse and interfere throughout the film. Intersecting waves create   of use for memory and computation. Memristic transponders distributed on the thin film respond to
six wavepackets and they propagate outwards in specific directions.    threshold tunnel magnetoresistance values, thereby allowing spin-wave detection and creating new
This figure shows the amplitude of one of the in-plane magnetic        excitation patterns. We show how groups of transponders create resonant (reverberating) spin-wave
components, |m x|.
                                                                       interference patterns that may be used for polychronous wave computation and information storage.




                                                                                                                                                             Nanotechnology   19
Nanotechnology Highlights 2011




                                                                   Focused ion beam-fabricated Au micro/




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                                                                   nanostructures used as a surface enhanced




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                                                                   detection of molecules and influenza virus
                                                                   Ying-Yi Lin, Jiunn-Der Liao, Yu-Hung Ju, Chia-Wei Chang and Ai-Li Shiau


                                                                   2011 Nanotechnology 22 185308

                                                                   The focused ion beam (FIB) technique was used to precisely fabricate patterned Au micro/
                                                                   nanostructures (fibAu). The effects of surface enhanced Raman scattering (SERS) on the fibAu
                                                                   samples were investigated by adjusting the geometrical, dimensional, and spacing factors.
FE-SEM micrograph of one of the Au samples pattered using a        The SERS mechanism was evaluated using low-concentration rhodamine 6G (R6G) molecules,
focused ion beam (FIB). The marked surface area representing the   physically adsorbed or suspended on/within the micro/nanostructures. The results indicated that
diameter of the Raman laser spot is approximately 1 μm2.           for detecting R6G molecules, hexagon-like micro/nanostructures induced a higher electromagnetic
                                                                   mechanism (EM) due to the availability of multiple edges and small curvature. By decreasing the
                                                                   dimensions from 300 to 150 nm, the laser-focused area contained an increasing number of micro/
                                                                   nanostructures and therefore intensified the excitation of SERS signals. Moreover, with an optimized
                                                                   geometry and dimensions of the micro/nanostructures, the relative intensity/surface area value
                                                                   reached a maximum as the spacing was 22 nm. An exponential decrease was found as the spacing
                                                                   was increased, which most probably resulted from the loss of EM. The spacing between the micro/
                                                                   nanostructures upon the fibAu was consequently regarded as the dominant factor for the detection of
                                                                   R6G molecules. By taking an optimized fibAu to detect low-concentration influenza virus, the amino
                                                                   acids from the outermost surface of the virus can be well distinguished through the SERS mechanism.


                                                                   Rapid turnaround scanning probe nanolithography
                                                                   Philip C Paul, Armin W Knoll, Felix Holzner, Michel Despont and Urs Duerig


                                                                   2011 Nanotechnology 22 275306

                                                                   Scanning probe nanolithography (SPL) has demonstrated its potential in a variety of applications
                                                                   like 3D nanopatterning, ‘direct development’ lithography, dip-pen deposition or patterning of self-
                                                                   assembled monolayers. One of the main issues holding back SPL has been the limited throughput
Cantilever sensor used in the experiment.                          for patterning and imaging. Here we present a complete lithography and metrology system based
                                                                   on thermomechanical writing into organic resists. Metrology is carried out using a thermoelectric
                                                                   topography sensing method. More specifically, we demonstrate a system with a patterning pixel clock
                                                                   of 500 kHz, 20 mm s−1 linear scan speed, a positioning accuracy of 10 nm, a read-back frequency
                                                                   bandwidth of 100 000 line-pairs s−1 and a turnaround time from patterning to qualifying metrology of
                                                                   1 min. Thus, we demonstrate a nanolithography system capable of implementing rapid turnaround.



                                                                   Single and multilayer metamaterials fabricated by
                                                                   nanoimprint lithography
                                                                   I Bergmair, B Dastmalchi, M Bergmair, A Saeed, W Hilber, G Hesser, C Helgert, E Pshenay-Severin,
                                                                   T Pertsch, E B Kley, U Hübner, N H Shen, R Penciu, M Kafesaki, C M Soukoulis, K Hingerl, M Muehlberger
                                                                   and R Schoeftner


                                                                   2011 Nanotechnology 22 325301

                                                                   We demonstrate for the first time a fast and easy nanoimprint lithography (NIL) based stacking
SEM image of Swiss-cross shaped negative index material (NIM).     process of negative index structures like fishnet and Swiss-cross metamaterials. The process takes
The scale bar is 200 nm.                                           a few seconds, is cheap and produces three-dimensional (3D) negative index materials (NIMs) on
                                                                   a large area which is suitable for mass production. It can be performed on all common substrates
                                                                   even on flexible plastic foils. This work is therefore an important step toward novel and breakthrough
                                                                   applications of NIMs such as cloaking devices, perfect lenses and magnification of objects using NIM
                                                                   prisms. The optical properties of the fabricated samples were measured by means of transmission
                                                                   and reflection spectroscopy. From the measured data we retrieved the effective refractive index which
                                                                   is shown to be negative for a wavelength around 1.8 μm for the fishnet metamaterial while the Swiss-
                                                                   cross metamaterial samples show a distinct resonance at wavelength around 1.4 μm.
20    Nanotechnology
                                                                                               Nanotechnology Highlights 2011




Sensing and actuating
Large surface area and high sensitivity to changes in the     The sensitivity of nanowire properties to their
environment are winning attributes for nanomaterials          surroundings has leant them to analyte-specific
in nanoscale sensing and actuating devices. Our               sensing applications. Now researchers in the UK
understanding of the properties of nanomaterials and          have applied principal component analysis and
ways to manipulate them is constantly advancing, and          quadratic discriminant analysis to arrays of differently
countless different avenues for how to apply them are         functionalized nanowires to develop nanosensors
teaming with new ideas.                                       with learning capabilities. In their proof-of-principle
                                                              demonstration they show that even non-functionalized
The extraordinary intrinsic properties of nanomaterials       nanowires can distinguish between solvents in
allow enhanced sensing in many respects, including            completely uncontrolled ambient conditions with the
resolution and sensitivity. Researchers in the US             help of elementary machine learning.
have taken advantage of the electrical and thermal
conductivity of carbon nanotubes for thermographic            A lot of current progress exploits combinations of more
structural testing of carbon nanotube composite               than one approach. A collaboration of researchers in
materials using resistive heating. The method allows in       the UK use a scanning probe held in two optical traps
situ low-power non-destructive monitoring of structural       to achieve the resolution of scanning probe microscopy
health with state-of-the-art resolution to help prevent       with the force sensitivity of photonic force microscopy.
structural failures in engineering materials.                 The orientation of the probe can be controlled using
                                                              holographic beam shaping, allowing the technique to
Ever increasing control in fabrication methods has            be applied to highly curved and challenging surface
helped innovations that exploit nanomaterial properties.      geometries.
Researchers in the US report a simple fabrication
method for a vertically aligned nanowire array sensor         Browsing this year’s highlights, it may seem that as fast
with a porous top electrode that is sensitive to 10 ppb.      as the intricacies in nanoscale phenomena are revealed,
The structure allows even penetration of the analyte          device technologies to exploit them are developed. And
through the top electrode while maintaining consistent        the more we learn about nanomaterials, the more we
connections to all of the nanowires.                          realize that there is to learn. This bodes well for further
                                                              inspiring innovations in sensing and actuating in the
                                                              future.



                        Section scope
                         The possibility of using nanotechnology to convey and enhance information to a
                         macroscopic scale has driven a wave of research into fabrication and optimization of
                         nanoscale sensor devices. Devices have been developed for such wide ranging applications
                         as the detection of gases, such as ethanol and oxygen; biomolecules, like DNA; and
                         mechanical forces. Progress is leading to applications in a multitude of fields such as food
                         safety and gas alarms. The unique properties of nano materials, such as exceptional strength
 Section Editor: Juergen
                         and massive surface-to-volume ratio compared with their macroscale counterparts, has
 Brugger                 allowed great enhancement of the sensitivity of sensors in many fields. This section invites
                         submissions that show significant enhancement of the sensing capabilities of applied nano
 systems, as well as novel applications of nanoscale devices to the detection of mechanical phenomena, biological,
 material and chemical species.




                                                                                                            Nanotechnology   21
Nanotechnology Highlights 2011




                                                                   A carbon-nanotube-based sensor array for formaldehyde
                                                                   detection
                                                                   Yijiang Lu, M Meyyappan and Jing Li


                                                                   2011 Nanotechnology 22 055502

                                                                   We have fabricated a sensor array consisting of 32 sensor elements with pristine, doped and
                                                                   metal-loaded single-wall carbon nanotubes as sensing materials. The sensor elements consist of
                                                                   interdigitated electrodes with varying finger widths and gaps. The chemiresistor-type sensors provide
                                                                   a significant response to formaldehyde at concentrations down to 10 ppb in air with rapid response
                                                                   and recovery times.



A 32-element sensor array chip with interdigitated electrodes.




                                                                   Multi-physics damage sensing in nano-




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                                                                   engineered structural composites




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                                                                   Roberto Guzmán de Villoria, Namiko Yamamoto, Antonio Miravete and Brian L Wardle


                                                                   2011 Nanotechnology 22 185502

                                                                   Non-destructive evaluation techniques can offer viable diagnostic and prognostic routes to
                                                                   mitigating failures in engineered structures such as bridges, buildings and vehicles. However,
                                                                   existing techniques have significant drawbacks, including poor spatial resolution and limited in situ
                                                                   capabilities. We report here a novel approach where structural advanced composites containing
A center-impacted composite plate with barely visible impact       electrically conductive aligned carbon nanotubes (CNTs) are ohmically heated via simple electrical
damage was inspected via thermography to reveal the presence of    contacts, and damage is visualized via thermographic imaging. Damage, in the form of cracks and
internal damage.
                                                                   other discontinuities, usefully increases resistance to both electrical and thermal transport in these
                                                                   materials, which enables tomographic full-field damage assessment in many cases. Characteristics
                                                                   of the technique include the ability for real-time measurement of the damage state during loading,
                                                                   low-power operation (e.g. 15 °C rise at 1 W), and beyond state-of-the-art spatial resolution for sensing
                                                                   damage in composites. The enhanced thermographic technique is a novel and practical approach
                                                                   for in situ monitoring to ascertain structural health and to prevent structural failures in engineered
                                                                   structures such as aerospace and automotive vehicles and wind turbine blades, among others.



                                                                   Surface imaging using holographic optical tweezers
                                                                   D B Phillips, J A Grieve, S N Olof, S J Kocher, R Bowman, M J Padgett, M J Miles and D M Carberry


                                                                   2011 Nanotechnology 22 285503

                                                                   We present an imaging technique using an optically trapped cigar-shaped probe controlled using
                                                                   holographic optical tweezers. The probe is raster scanned over a surface, allowing an image to be taken
                                                                   in a manner analogous to scanning probe microscopy (SPM), with automatic closed loop feedback
                                                                   control provided by analysis of the probe position recorded using a high speed CMOS camera. The
                                                                   probe is held using two optical traps centred at least 10 μm from the ends, minimizing laser illumination
                                                                   of the tip, so reducing the chance of optical damage to delicate samples. The technique imparts less
                                                                   force on samples than contact SPM techniques, and allows highly curved and strongly scattering
                                                                   samples to be imaged, which present difficulties for imaging using photonic force microscopy. To
                                                                   calibrate our technique, we first image a known sample—the interface between two 8 μm polystyrene
A three-dimensional surface image following the scan of the side   beads. We then demonstrate the advantages of this technique by imaging the surface of the soft
wall of a Pseudopediastrum unit cell.                              alga Pseudopediastrum. The scattering force of our laser applied directly onto this sample is enough
                                                                   to remove it from the surface, but we can use our technique to image the algal surface with minimal
                                                                   disruption while it is alive, not adhered and in physiological conditions. The resolution is currently
                                                                   equivalent to confocal microscopy, but as our technique is not diffraction limited, there is scope for
                                                                   significant improvement by reducing the tip diameter and limiting the thermal motion of the probe.

22    Nanotechnology
                                                                                                                                                Nanotechnology Highlights 2011




                                                                          Silicon nanowire arrays as learning chemical




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                                                                          vapour classifiers




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                                                                          A O Niskanen, A Colli, R White, H W Li, E Spigone and J M Kivioja


                                                                          2011 Nanotechnology 22 295502

                                                                          Nanowire field-effect transistors are a promising class of devices for various sensing applications.
Etched NW channel obtained by the superposition of randomly
                                                                          Apart from detecting individual chemical or biological analytes, it is especially interesting to use
oriented NW masks. The scalebar is 500 nm. The metal electrode is
on the left highlighted by a yellow shade.                                multiple selective sensors to look at their collective response in order to perform classification into
                                                                          predetermined categories. We show that non-functionalised silicon nanowire arrays can be used to
                                                                          robustly classify different chemical vapours using simple statistical machine learning methods. We
                                                                          were able to distinguish between acetone, ethanol and water with 100% accuracy while methanol,
                                                                          ethanol and 2-propanol were classified with 96% accuracy in ambient conditions.




                                                                          Mass and stiffness calibration of nanowires using
                                                                          thermally driven vibration
                                                                          D R Kiracofe, M M Yazdanpanah and A Raman


                                                                          2011 Nanotechnology 22 295504

                                                                          Cantilevered or suspended nanowires show promise for force or mass sensing applications due to
                                                                          their small mass, high force sensitivity and high frequency bandwidth. To use these as quantitative
                                                                          sensors, their bending stiffness or mass must be calibrated experimentally, often using thermally
For a perfectly circular wire, the thermal vibration will have the same   driven vibration. However, this can be difficult because nanowires are slightly asymmetric, which
amplitude in any direction. But for any asymmetry, however small,
                                                                          results in two spatially orthogonal bending eigenmodes with closely spaced frequencies. This
the thermal vibration will be larger along one principal axis than
along the other. Moreover, the measurement direction may be at            asymmetry presents problems for traditional stiffness calibration methods, which equate the
some angle θ with respect to the principal axes.                          measured thermal vibration spectrum near a resonance to that of a single eigenmode. Moreover,
                                                                          the principal axes may be arbitrarily rotated with respect to the measurement direction. In this work,
                                                                          the authors propose a method for calibrating the bending stiffness and mass of such nanowires’
                                                                          eigenmodes using a single measurement taken at an arbitrary orientation with respect to the
                                                                          principal axes.



                                                                          Periodically porous top electrodes on vertical
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                                                                          nanowire arrays for highly sensitive
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                                                                          gas detection
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                                                                          Hyun Jin In, Christopher R Field and Pehr E Pehrsson


                                                                          2011 Nanotechnology 22 355501

                                                                          Nanowires of various materials and configurations have been shown to be highly effective in the
                                                                          detection of chemical and biological species. In this paper, we report a novel, nanosphere-enabled
SEM image of the sensor, showing the porous top electrode (PTE)           approach to fabricating highly sensitive gas sensors based on ordered arrays of vertically aligned
and the silicon nanowire (SiNW) array underneath.                         silicon nanowires topped with a periodically porous top electrode. The vertical array configuration
                                                                          helps to greatly increase the sensitivity of the sensor while the pores in the top electrode layer
                                                                          significantly improve sensing response times by allowing analyte gases to pass through freely.
                                                                          Herein, we show highly sensitive detection to both nitrogen dioxide (NO2) and ammonia (NH3) in
                                                                          humidified air. NO2 detection down to 10 parts per billion (ppb) is demonstrated and an order-of-
                                                                          magnitude improvement in sensor response time is shown in the detection of NH3.




                                                                                                                                                                Nanotechnology   23
Nanotechnology Highlights 2011




Materials: synthesis or self-assembly
  Sponsored by                   Using AIXTRON’s CVD and PECVD systems, graphene, carbon nanotubes and
                                 semiconducting nanowires can be controllably grown, enabling applications such as
                                 nano-transistors, interconnects, sensors, displays, thermal interfaces, electron guns,
                                 microfluidics and microwave amplifiers. Also see the Electronics and photonics category
                                 on p11. Visit www.aixtron.com.



Controlled synthesis is one of the driving forces behind             Template forming can be costly and removal of the
a great deal of current progress in nanotechnology.                  template tends to cause aggregation of one-dimensional
Feynman’s proposition that “there’s plenty of room at the            nanomaterials. Researchers in China exploit the
bottom” is commonly claimed to have initiated a burst                intrinsic anisotropic crystal structure of Te and a
of activity in manipulating matter at the nanoscale. More            platinum substrate for nanowire deposition. Gold/
than 50 years later the field continues to fascinate.                tellurium nanorods could then be formed by chemical
                                                                     replacement reactions. The researchers demonstrate
One enduring source of inspiration in nanoscale synthesis            surface-enhanced Raman scattering detection over a
is biological self assembly. Along these lines the ordered           large area with the resulting structure.
arrangement of colloidal nanoparticles has attracted a
great deal of interest. A collaboration of researchers in            Boron nitride has a number of intriguing properties.
Iran, Denmark and Australia has studied the evaporation-             The ultrathin dimensions of free-standing single-atomic
induced assembly of binary colloidal assemblies on a                 layer boron nitride films inspired researchers in the
hydrophobic or hydrophilic substrate. They identify the              UK to investigate its applications as a transmission
roles of electrostatic and capillary forces and factors that         electron microscope supporting film. They analyse the
affect crystal formation and ordering.                               phase contrast images and resulting moiré interference
                                                                     patterns that arise from an electron beam propagating
Researchers in Germany have explored the selectivity of              through a crystalline boron nitride film with Mn-doped
GaN growth by plasma-assisted molecular beam epitaxy.                ZnSe nanocrystals deposited on top.
They optimize the conditions for nanowire growth in holes
of a mask with all parasitic growth in between holes                 Many signature materials in nanoscale research were
suppressed. The work provides an alternative to growth               discovered by a combination of inspiration and accident.
of ordered arrays of nanoparticles seeded by catalysts,              As the papers in these highlights demonstrate fast, cheap,
which can introduce impurities.                                      scalable production of purpose-designed enhanced
                                                                     materials is now becoming increasing achievable.



                              Section scope
                              The success of nanotechnology in real-world applications hinges on the development of
                              methods that allow for cheaper, faster, greener and more reliable modes of fabrication of high-
                              quality nanostructures for implementation into devices. The synthesis of nanoscale materials
                              is now performed via a huge variety of methods, including but not limited to, physico-chemical,
                              optical, and mechanical variations. This section continues to publish papers that demonstrate
                              progress towards the development of previously unattainable and novel fabrication standards
 Section Editor: Stanislaus
 Wong                         for existing nanostructures, as well as the fabrication of new structures wherein a clear,
                              important and practical application can be convincingly demonstrated.




24   Nanotechnology
                                                                                                                                                Nanotechnology Highlights 2011




                                                                        Selective-area catalyst-free MBE growth of GaN nanowires
                                                                        using a patterned oxide layer
                                                                        T Schumann, T Gotschke, F Limbach, T Stoica and R Calarco


                                                                        2011 Nanotechnology 22 095603

                                                                        GaN nanowires (NWs) were grown selectively in holes of a patterned silicon oxide mask, by
                                                                        rf-plasma-assisted molecular beam epitaxy (PAMBE), without any metal catalyst. The oxide was
                                                                        deposited on a thin AlN buffer layer previously grown on a Si(111) substrate. Regular arrays of
                                                                        holes in the oxide layer were obtained using standard e-beam lithography. The selectivity of growth
                                                                        has been studied varying the substrate temperature, gallium beam equivalent pressure and
                                                                        patterning layout. Adjusting the growth parameters, GaN NWs can be selectively grown in the holes
SEM micrographs of GaN nanowires selectively grown over 4 hours         of the patterned oxide with complete suppression of the parasitic growth in between the holes. The
through pre-patterned 60 nm diameter holes in a silicon oxide           occupation probability of a hole with a single or multiple NWs depends strongly on its diameter.
mask.                                                                   The selectively grown GaN NWs have one common crystallographic orientation with respect to the
                                                                        Si(111) substrate via the AlN buffer layer, as proven by x-ray diffraction (XRD) measurements. Based
                                                                        on the experimental data, we present a schematic model of the GaN NW formation in which a GaN
                                                                        pedestal is initially grown in the hole.




                                                                        Utilizing boron nitride sheets as thin supports for high
                                                                        resolution imaging of nanocrystals
                                                                        Yimin A Wu, Angus I Kirkland, Franziska Schäffel, Kyriakos Porfyrakis, Neil P Young, G Andrew D Briggs
                                                                        and Jamie H Warner


                                                                        2011 Nanotechnology 22 195603

                                                                        We demonstrate the use of thin BN sheets as supports for imaging nanocrystals using low voltage
                                                                        (80 kV) aberration-corrected high resolution transmission electron microscopy. This provides an
                                                                        alternative to the previously utilized 2D crystal supports of graphene and graphene oxide. A simple
                                                                        chemical exfoliation method is applied to get few layer boron nitride (BN) sheets with micrometer-
                                                                        sized dimensions. This generic approach of using BN sheets as supports is shown by depositing
                                                                        Mn doped ZnSe nanocrystals directly onto the BN sheets and resolving the atomic structure from
                                                                        both the ZnSe nanocrystals and the BN support. Phase contrast images reveal moiré patterns of
HRTEM image showing the crystalline structure of several Mn doped
                                                                        interference between the beams diffracted by the nanocrystals and the BN substrate that are used to
nanocrystals on the surface of disc shaped BN sheets. The atomic
structure of both the nanocrystals and the BN sheet is visible in the   determine the relative orientation of the nanocrystals with respect to the BN sheets and interference
image.                                                                  lattice planes. Double diffraction is observed and has been analyzed.




                                                                        Role of proteins in controlling selenium nanoparticle size
                                                                        J Dobias, E I Suvorova and R Bernier-Latmani


                                                                        2011 Nanotechnology 22 195605

                                                                        This work investigates the potential for harnessing the association of bacterial proteins to biogenic
                                                                        selenium nanoparticles (SeNPs) to control the size distribution and the morphology of the resultant
                                                                        SeNPs. We conducted a proteomic study and compared proteins associated with biogenic SeNPs
                                                                        produced by E. coli to chemically synthesized SeNPs as well as magnetite nanoparticles. We
                                                                        identified four proteins (AdhP, Idh, OmpC, AceA) that bound specifically to SeNPs and observed a
                                                                        narrower size distribution as well as more spherical morphology when the particles were synthesized
                                                                        chemically in the presence of proteins. A more detailed study of AdhP (alcohol dehydrogenase
                                                                        propanol-preferring) confirmed the strong affinity of this protein for the SeNP surface and revealed
STEM image of chemogenic Se nanoparticles with controlled size
when after synthesis in the presence of alcohol dehydrogenase,
                                                                        that this protein controlled the size distribution of the SeNPs and yielded a narrow size distribution
propanol-preferring (AdhP) protein.                                     with a three-fold decrease in the median size. These results support the assertion that protein may
                                                                        become an important tool in the industrial-scale synthesis of SeNPs of uniform size and properties.




                                                                                                                                                                Nanotechnology   25
Nanotechnology Highlights 2011




                                                                   Electrostatic and capillary force directed tunable 3D binary
                                                                   micro- and nanoparticle assemblies on surfaces
                                                                   G Singh, S Pillai, A Arpanaei and P Kingshott


                                                                   2011 Nanotechnology 22 225601

                                                                   We report a simple, rapid and cost-effective method based on evaporation induced assembly to
                                                                   grow 3D binary colloidal assemblies on a hydrophobic/hydrophilic substrate by simple drop casting.
                                                                   The evaporation of a mixed colloidal drop results in ring-like or uniform area deposition depending
                                                                   on the concentration of particles, and thus assembly occurs at the periphery of a ring or uniformly
                                                                   all over the drop area. Binary colloidal assemblies of different crystal structure are successfully
                                                                   prepared over a wide range of size ratios (γ = small/large) from 0.06 to 0.30 by tuning the γ of
SEM image of a binary colloidal assembly (BCA) formed on an        the micro- and nanoparticles used during assembly. The growth mechanism of 3D binary colloidal
octadecyltrichlorosilane (OTS) modified silicon wafer. The image
shows 2 μm carboxyl polystyrene (COOH–PS) and 400 nm amine
                                                                   assemblies is investigated and it is found that electrostatic forces facilitate assembly formation until
polystyrene (NH2–PS) particles. Scale bar is 1 μm.                 the end of the evaporation process, with capillary forces also playing a role. In addition, the effects of
                                                                   solvent type, humidity, and salt concentration on crystal formation and ordering behaviour are also
                                                                   examined. Furthermore, long range, highly ordered binary colloidal assemblies can be fabricated by
                                                                   the choice of a low conducting solvent combined with evaporation induced assembly.



                                                                   Hydrothermally grown ZnO nanostructures on few-layer
                                                                   graphene sheets
                                                                   Yong-Jin Kim, Hadiyawarman, Aram Yoon, Miyoung Kim, Gyu-Chul Yi and Chunli Liu


                                                                   2011 Nanotechnology 22 245603

                                                                   This study describes the hydrothermal growth of ZnO nanostructures on few-layer graphene sheets
                                                                   and their optical and structural properties. The ZnO nanostructures were grown on graphene sheets
                                                                   of a few layers thick (few-layer graphene) without a seed layer. By changing the hydrothermal growth
                                                                   parameters, including temperature, reagent concentration and pH value of the solution, we readily
                                                                   controlled the dimensions, density and morphology of the ZnO nanostructures. More importantly,
                                                                   single-crystalline ZnO nanostructures grew directly on graphene, as determined by transmission
                                                                   electron microscopy. In addition, from the photoluminescence and cathodoluminescence spectra,
                                                                   strong near-band-edge emission was observed without any deep-level emission, indicating that the
                                                                   ZnO nanostructures grown on few-layer graphene were of high optical quality.

SEM of a ZnO nanorod on few-layer graphene (FLG) sheet.



                                                                   Direct growth of tellurium nanorod arrays on Pt/FTO/glass
                                                                   through a surfactant-assisted chemical reduction
                                                                   Hongmei Liu, Boming Zeng and Falong Jia


                                                                   2011 Nanotechnology 22 305608

                                                                   Uniform tellurium nanorod arrays (TNA) have been successfully deposited directly on Pt/FTO
                                                                   (F-doped SnO2)/glass substrate through a facile surfactant-assisted approach, which involved
                                                                   chemical reduction of TeO32− ions by hydrazine hydrate. The whole synthesis process is highly
                                                                   repeatable and performed simply by immersing the Pt/FTO/glass in the solution for a certain
SEM image of Te powder collected from the solution with 5 mM       time. During the growth of TNA, Pt catalyzed the reduction of TeO32− ions by hydrazine hydrate and
cetyltrimethylammonium bromide (CTAB) with no substrate. The       Te nanoparticles were deposited firmly on the substrate at first. Then, under the regulation of the
morphology of the Te sample is an aggregate formed by the growth
                                                                   surfactant (cetyltrimethylammonium bromide, CTAB), the deposited Te grew into nanorod arrays
of nanorods and nanoparticles together.
                                                                   and adhered firmly to the substrate. Similar Te nanorod arrays could also grow on a Pd substrate
                                                                   which has the same catalytic performance as that of Pt. The as-synthesized TNA could be used as
                                                                   a good template to synthesize platinum-and gold-coated nanorods through convenient galvanic
                                                                   replacement. As a demonstration of potential application, the gold/tellurium nanorods showed
                                                                   uniform surface-enhanced Raman scattering (SERS) using rhodamine 6G (Rh6G) as the analyte. This
                                                                   approach provides a simple route for the growth of standing Te nanorods on a substrate, which may
                                                                   be used for the synthesis of other standing one-dimensional materials through a similar mechanism.

26    Nanotechnology
                                                                                               Nanotechnology Highlights 2011




Materials: properties, characterization or tools
Nanomaterials are constantly revealing more and               Back in the 1980s developments in scanning probe
more unusual properties. At the same time, tools for          microscopy first revealed the reality of the nanoworld.
probing nanomaterials are rising to the challenge with        Atomic force microscopy remains an invaluable tool, but
increasingly sophisticated innovations.                       soft material specimens are a challenge. Researchers
                                                              in the US have reported an approach based on atomic
Quantum dots have recently emerged as a selective,            force microscopy for mapping material moduli. They
high-contrast and sensitive fluorescent marker for            use a quartz crystal resonator as a force sensor that
fingerprint detection. However, the current approach to       meets the requirements of both high sensitivity and low
synthesizing the CdTe quantum dots results in negatively      compliance for nanoscale investigation of soft materials.
charged entities that are repelled by the negative
charge of amino acid residues in alkaline conditions.         A collaboration of researchers in Switzerland and
Researchers in China have devised a procedure for             Greece has used a magnetic cantilever to determine
synthesizing positively charged quantum dots and              the paramagnetism and soft and hard ferromagnetism
demonstrated their improved effectiveness for fingerprint     of sample systems. They also demonstrate the
detection.                                                    effectiveness of the technique to measure the
                                                              magnetic properties of the bacteria Magnetospirrillum
Researchers in Korea have used a laser treatment              gryphiswalsense.
to improve the properties of carbon nanotube films.
Solution-based deposition of carbon nanotubes uses a          Masaru Ibuka, co-founder of Sony Corporation, once
surfactant to produce a stable solution. The surfactant is    said: “creativity comes from looking for the unexpected
insulating and must be removed, but rinsing in acid often     and stepping outside your own experience.” All sorts
washes away the carbon-nanotube films reducing the            of unexpected twists and turns continue to arise in the
throughput. Myungo Joo and Myeongkyu Lee show that a          properties of nanomaterials and in the applications of
pulsed Nd:YAG laser can effectively remove surfactants        the tools to measure them. This selection of highlights
improving the film’s conductivity and transmissivity.         describes just a few from cutting-edge nanoscale
                                                              research in 2011.



                        Section scope
                        Much of the progress in current technology is based on the unique and extraordinary
                        properties of nanoscale structures and systems. This section is devoted to research that
                        provides a deeper understanding of the way nanostructured materials interact and the
                        factors that govern their behaviour. The section includes experimental research on the
                        optical, magnetic, electrical, mechanical and quantum properties of nanostructures and
                        systems, and looks at ways of manipulating the response to changes in the surrounding
                        environment and external triggers for device applications. The section also covers theoretical
 Section Editor: Mervyn studies that reveal potential new properties that have not yet been experimentally observed,
 Miles                  as well as helping to explain the physics behind the reported properties of nanomaterials.
 We also encourage submissions on new ways of characterizing the nanoscale structures and properties including
 novel ways to image materials.




                                                                                                            Nanotechnology   27
Nanotechnology Highlights 2011




                                                                   The synthesis of newly modified CdTe quantum dots and
                                                                   their application for improvement of latent fingerprint
                                                                   detection
                                                                   Feng Gao, Jiaxing Han, Jun Zhang, Qun Li, Xiufeng Sun, Jincheng Zheng, Liru Bao, Xin Li and Zhiliang Liu


                                                                   2011 Nanotechnology 22 075705

                                                                   Motivated by the urgent demand for the detection of latent fingerprints using fluorescence-based
                                                                   nanotechnology, this work was devoted to developing a simple synthetic approach to obtain
                                                                   positively charged CdTe QDs with enhanced fluorescence and affinity for the improvement of latent
                                                                   fingerprint detection. Through this synthetic method, the positively charged CdTe–COONH3NH3 + QDs
                                                                   were successfully achieved by using hydrazine hydrate as both the surface stabilizer and pH adjuster
                                                                   during the preparation process. In comparison to the negatively charged CdTe–COO − QDs prepared
                                                                   by using sodium hydroxide as the pH adjuster, the CdTe–COONH3NH3 + QDs showed enhanced
                                                                   fluorescence. The effectiveness of CdTe–COO − and CdTe–COONH3NH3 + QDs for detection of latent
                                                                   fingerprints present on a large variety of smooth objects was systematically and comparatively
                                                                   studied. The results indicate that the detection of latent fingerprints by using CdTe–COONH3NH3 +
                                                                   QDs as fluorescent labeling marks was greatly enhanced, and more characteristic finger ridge details
                                                                   were detected and identified due to their enhanced affinity with latent fingerprints, in comparison
                                                                   to the detection by using CdTe–COO − QDs as fluorescent labeling marks. The CdTe–COONH3NH3 +
Detection of latent fingerprint on a smooth black rubber surface   QDs show superior detection capability than the CdTe–COO − QDs, which greatly improves the
treated with an CdTe–COONH3NH+3 QD aqueous solution.               applicability of CdTe QDs for practical application in latent fingerprint detection.




                                                                   Improvement of toughness and electrical properties of
                                                                   epoxy composites with carbon nanotubes prepared by
                                                                   industrially relevant processes
                                                                   R Hollertz, S Chatterjee, H Gutmann, T Geiger, F A Nüesch and B T T Chu


                                                                   2011 Nanotechnology 22 125702

                                                                   The addition of carbon nanotubes (CNTs) to polymeric matrices or master batches has the potential
                                                                   to provide composites with novel properties. However, composites with a uniform dispersion
                                                                   of CNTs have proved to be difficult to manufacture, especially at an industrial scale. This paper
                                                                   reports on processing methods that overcome problems related to the control and reproducibility of
                                                                   dispersions. By using a high pressure homogenizer and a three-roll calendaring mill in combination,
                                                                   CNT reinforced epoxies were fabricated by mould casting with a well dispersed nanofiller
                                                                   content from 0.1 to 2 wt%. The influence of the nano-carbon reinforcements on toughness and
TEM micrograph of 0.5 wt% MWNT/epoxy composite processed by
three-roll milling.
                                                                   electrical properties of the CNT/epoxies was studied. A substantial increase of all mechanical
                                                                   properties already appeared at the lowest CNT content of 0.1 wt%, but further raising the
                                                                   nanofiller concentration only led to moderate further changes. The most significant enhancement
                                                                   was obtained for fracture toughness, reaching up to 82%. The low percolation thresholds were
                                                                   confirmed by electrical conductivity measurements on the same composites yielding a threshold
                                                                   value of only about 0.01 wt%. As corroborated by a thorough microscopic analysis of the
                                                                   composites, mechanical and electrical enhancement points to the formation of an interconnected
                                                                   network of agglomerated CNTs.




28    Nanotechnology
                                                                                                                                           Nanotechnology Highlights 2011




                                                                        Force scanning: a rapid, high-resolution




                                                                                                                                                          na
                                                                                                                                                          Fe tec
                                                                                                                                                            no
                                                                                                                                                             at hw
                                                                        approach for spatial mechanical property




                                                                                                                                                               ur e
                                                                                                                                                                 ed b
                                                                        mapping




                                                                                                                                                                   on .org
                                                                        E M Darling


                                                                        2011 Nanotechnology 22 175707

                                                                        Atomic force microscopy (AFM) can be used to co-localize mechanical properties and topographical
                                                                        features through property mapping techniques. The most common approach for testing biological
                                                                        materials at the microscale and nanoscale is force mapping, which involves taking individual force
High-resolution elastic modulus mapping of a cell. AFM height           curves at discrete sites across a region of interest. The limitations of force mapping include long
images were overlaid with elastic modulus maps to determine
localized mechanical properties for a single cell. This 128 × 128 pt.
                                                                        testing times and low resolution. While newer AFM methodologies, like modulated scanning and
scan was collected over 6 min using a scan rate of 2 Hz and             torsional oscillation, circumvent this problem, their adoption for biological materials has been
demonstrates the possible applications of the force scanning            limited. This could be due to their need for specialized software algorithms and/or hardware. The
technique. The single adipose-derived stem cell (ASC) exhibited         objective of this study is to develop a novel force scanning technique using AFM to rapidly capture
lower moduli (0.5–1 kPa) over the nucleus and perinuclear region
                                                                        high-resolution topographical images of soft biological materials while simultaneously quantifying
and higher moduli near its edges (3–10 kPa).
                                                                        their mechanical properties. Force scanning is a straightforward methodology applicable to a
                                                                        wide range of materials and testing environments, requiring no special modification to standard
                                                                        AFMs. Essentially, if a contact-mode image can be acquired, then force scanning can be used to
                                                                        produce a spatial modulus map. The current study first validates this technique using agarose gels,
                                                                        comparing results to ones achieved by the standard force mapping approach. Biologically relevant
                                                                        demonstrations are then presented for high-resolution modulus mapping of individual cells, cell–cell
                                                                        interfaces, and articular cartilage tissue.




                                                                        Laser treatment of solution-deposited carbon nanotube
                                                                        thin films for improved conductivity and transparency
                                                                        Myungo Joo and Myeongkyu Lee


                                                                        2011 Nanotechnology 22 265709

                                                                        Solution-deposited single-walled carbon nanotube (SWCNT) films contain a surfactant material
                                                                        and it should be removed by a post-deposition treatment to improve the conductivity. We here
                                                                        report that the sodium dodecyl sulfate (SDS) surfactant in SWCNT films can be completely removed
SEM image of a single-walled carbon nanotube (SWCNT) film
                                                                        by a pulsed Nd:YAG laser (wavelength = 1064 nm, pulse width = 99 ms). SWCNT films were spray-
showing that the sodium dodecyl sulfate (SDS) surfactant has been       coated onto a glass substrate and were scanned by a laser beam of 2 mm size. In this process,
completely removed by a pulsed Nd:YAG laser with a power of 137W.       individual nanotubes absorb the laser energy and generate heat to vaporize the surrounding
                                                                        surfactant. This mechanism was supported by the fact that the required pulse energy decreased
                                                                        as the SWCNT density increased. An encouraging feature is that unlike typical acid treatments,
                                                                        the laser treatment can improve not only the conductivity but also the transmittance. This might
                                                                        be associated with complete surfactant removal without leaving any particulate debris. For a
                                                                        film, the sheet resistance decreased from 1.07 kΩ/sq to 700 Ω/sq and its visible transmittance
                                                                        simultaneously increased by 4%.




                                                                                                Take an online tour at iopscience.org
                                                                                                to discover how IOPscience can help you.




                                                                                                                                                          Nanotechnology   29
Nanotechnology Highlights 2011




                                                                  Magnetic properties of nanomagnetic and biomagnetic
                                                                  systems analyzed using cantilever magnetometry
                                                                  Urs Gysin, Simon Rast, Andreas Aste, Thanassis Speliotis, Christoph Werle and Ernst Meyer


                                                                  2011 Nanotechnology 22 285715

                                                                  Magnetic properties of nanomagnetic and biomagnetic systems are investigated using cantilever
                                                                  magnetometry. In the presence of a magnetic field, magnetic films or particles deposited at the free
                                                                  end of a cantilever give rise to a torque on the mechanical sensor, which leads to frequency shifts
                                                                  depending on the applied magnetic field. From the frequency response, the magnetic properties of a
                                                                  magnetic sample are obtained. The magnetic field dependences of paramagnetic and ferromagnetic
                                                                  thin films and particles are measured in a temperature range of 5–320 K at a pressure below
                                                                  10 − 6 mbar. We present magnetic properties of the ferromagnetic materials Fe, Co and Ni at room
                                                                  temperature and also for the rare earth elements Gd, Dy and Tb at various temperatures. In addition,
TEM image of a magnetosome with a chain of magnetic
nanoparticles about 30 nm in diameter incorporated in the         the magnetic moments of magnetotactic bacteria are measured under vacuum conditions at room
Magnetospirillum gryphiswaldense bacteria.                        temperature. Cantilever magnetometry is a highly sensitive tool for characterizing systems with small
                                                                  magnetic moments. By reducing the cantilever dimensions the sensitivity can be increased by an
                                                                  order of magnitude.




                                                                  Probing near-surface nanoscale mechanical properties
                                                                  of low modulus materials using a quartz crystal resonator
                                                                  atomic force microscope
                                                                  Yen Peng Kong, Ling Chen and Albert F Yee


                                                                  2011 Nanotechnology 22 295709

                                                                  We describe the development of a technique for making indentations on the top 5–20 nm of
                                                                  the surfaces of relatively low modulus materials using a high spatial and force sensitivity atomic
                                                                  force microscope (AFM) whose optical cantilever has been replaced by a quartz crystal resonator
AFM image of polished Pb surface, which probably consists of an
oxide layer rather than pure Pb.
                                                                  (QCR). Unlike conventional optical-cantilever-based AFMs, the accuracy of this technique
                                                                  is not compromised by the compliance of the loading system due to the high stiffness of the
                                                                  QCR. To obtain material modulus values from the indentation results, we find the commonly
                                                                  used Oliver–Pharr model to be unsuitable because of our use of a sharp tip and relatively deep
                                                                  indentation. Instead, we develop a new analysis that may be more appropriate for the geometry
                                                                  we use as well as the non-linear constitutive behavior exhibited by the materials we examined. We
                                                                  calculated values for the moduli of several different materials, which we find to be consistent with
                                                                  the range of published data.




                                           “The Lab Talk article on nanotechweb.org resulted in many visits to my group website.
                                           I think it is a great venue to publicize our work.”
                                           Xun Yu Formerly of the Department of Mechanical and Industrial Engineering at the
                                           University of Minnesota Duluth, US; now at the Department of Mechanical and Energy
                                           Engineering College of Engineering University of North Texas (e-mail: Xun.yu@unt.edu)

                                           • Smart concrete detects traffic flow
                                             http://nanotechweb.org/cws/article/tech/40909




30    Nanotechnology
                                                                                                                                              Nanotechnology Highlights 2011




Media coverage
With the number of academic articles published worldwide increasing dramatically each year, it is becoming more
difficult for important research to be identified by academics, students and the general public. The Nanotechnology
editors actively work to identify important research and promote it to the interested community. As a result of these
efforts, articles from Nanotechnology have been featured by international news organizations (BBC, FOX, ABC), popular
scientific magazines (New Scientist, Nature News, Cosmos), scientific blogs and even on a YouTube video with more
than 1 million hits. Below are two examples of Nanotechnology articles that you may have seen in the news in 2011.


                                                                      The switching location of a bipolar memristor: chemical,
                                                                      thermal and structural mapping
                                                                      John Paul Strachan, Dmitri B Strukov, Julien Borghetti, J Joshua Yang, Gilberto Medeiros-Ribeiro
                                                                      and R Stanley Williams


                                                                      2011 Nanotechnology 22 254015

                                                                      Memristors are memory resistors promising a rapid integration into future memory technologies.
                                                                      However, progress is still critically limited by a lack of understanding of the physical processes
                                                                      occurring at the nanoscale. Here we correlate device electrical characteristics with local atomic
                                                                      structure, chemistry and temperature. We resolved a single conducting channel that is made up of
                                                                      a reduced phase of the as-deposited titanium oxide. Moreover, we observed sufficient Joule heating
                                                                      to induce a crystallization of the oxide surrounding the channel, with a peculiar pattern that finite
                                                                      element simulations correlated with the existence of a hot spot close to the bottom electrode, thus
Higher resolution scan of the bottom left corner of the junction
with a spatial mapping of the three observed phases of titanium
                                                                      identifying the switching location. This work reports direct observations in all three dimensions of the
oxide present. The color mapping of these regions is derived          internal structure of titanium oxide memristors.
from the Ti L 2,3 x-ray absorption image stack using singular value
decomposition procedures. A circle identifies the expected heated
region surrounding the conductive channel.




                                                                      Mirage effect from thermally modulated transparent
                                                                      carbon nanotube sheets
                                                                      Ali E Aliev, Yuri N Gartstein and Ray H Baughman


                                                                      2011 Nanotechnology 22 435704

                                                                      The single-beam mirage effect, also known as photothermal deflection, is studied using a free-
                                                                      standing, highly aligned carbon nanotube aerogel sheet as the heat source. The extremely low
                                                                      thermal capacitance and high heat transfer ability of these transparent forest-drawn carbon
                                                                      nanotube sheets enables high frequency modulation of sheet temperature over an enormous
                                                                      temperature range, thereby providing a sharp, rapidly changing gradient of refractive index in the
                                                                      surrounding liquid or gas. The advantages of temperature modulation using carbon nanotube sheets
                                                                      are multiple: in inert gases the temperature can reach > 2500 K; the obtained frequency range for
                                                                      photothermal modulation is ~100 kHz in gases and over 100 Hz in high refractive index liquids; and
                                                                      the heat source is transparent for optical and acoustical waves. Unlike for conventional heat sources
                                                                      for photothermal deflection, the intensity and phase of the thermally modulated beam component
                                                                      linearly depends upon the beam-to-sheet separation over a wide range of distances. This aspect
                                                                      enables convenient measurements of accurate values for thermal diffusivity and the temperature
                                                                      dependence of refractive index for both liquids and gases. The remarkable performance of nanotube
                                                                      sheets suggests possible applications as photo-deflectors and for switchable invisibility cloaks, and
                                                                      provides useful insights into their use as thermoacoustic projectors and sonar. Visibility cloaking is
                                                                      demonstrated in a liquid.



                                                                                                                                                              Nanotechnology   31
Nanotechnology Highlights 2011




Editorial board
Editor-in-chief                                                         Editorial board
Mark Reed, Yale University, New Haven, CT, USA                          Yoshio Bando, National Institute for Materials Science, Tsukuba, Japan
                                                                        Supriyo Bandyophadhyay, Virginia Commonwealth University, USA
                                                                        Karl Berggren, Massachusetts Institute of Technology, MA, USA
Section editors
                                                                        Christian Brosseau, Université de Bretagne Occidentale, France
Biology and medicine
                                                                        Jamal Deen, McMaster University, Hamilton, Canada
Jeffrey M Karp, Massachusetts Institute of Technology, MA, USA
                                                                        O Farokhzad, Harvard Medical School, MA, USA
Electronics and photonics
                                                                        George Grüner, University of California Los Angeles, USA
Meyya Meyyappan, NASA Ames Research Center, CA, USA
                                                                        Peter Grütter, McGill University, Canada
Energy at the nanoscale
                                                                        Devens Gust, Arizona State University, Tempe, AZ, USA
John Vajo HRL Laboratories LLC, CA, USA
                                                                        Seunghun Hong, Seoul National University, South Korea
Patterning and nanofabrication
                                                                        Ru Huang, Peking University, China
Sergei Kalinin, Oak Ridge National Laboratory, TN, USA
                                                                        Dae-Joon Kang, Sungkyunkwan University, South Korea
Sensing and actuation
                                                                        Frederik Krebs, Technical University of Denmark, Denamrk
Jürgen Brugger, Ecole Polytechnique Federale de Lausanne, Switzerland
                                                                        Ray LaPierre, McMaster University, Hamilton, Canada
Materials: synthesis or self-assembly
                                                                        Dan Peer, Tel Aviv University, Israel
Stanislaus Wong, State University of New York, NY, USA
                                                                        S Mark Spearing, University of Southampton, UK
Materials: properties, characterization and tools
                                                                        Michael Steigerwald, Columbia University, NY, USA
Mervyn J Miles, University of Bristol, UK
                                                                        Mahendra Sunkara, University of Louisville, KY, USA
                                                                        Mark Welland, University of Cambridge, UK
                                                                        George M Whitesides, Harvard University, Cambridge, MA, USA
                                                                        Chris Yip, University of Toronto, Canada




     Journal team




            Simon Buckmaster                       Nina Couzin                  David Cunnah                         Anna Demming
             Publishing editor                    Group publisher              Publishing editor                     Publishing editor




              Gemma Down                          Stephanie Gill                 Edward Jost                         Johnathan Keen
            Marketing executive                  Production editor           Group sales manager               Group publishing administrator




             Paul Macbeath                        Danny Turner                   James Tyrrell                      Alex Wotherspoon
             Publishing editor               Publishing administrator       Editor, nanotechweb.org                      Publisher




32   Nanotechnology
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                                                                                                                         • Gas-assisted material deposition and
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                                                                                                                         • RBS like analysis at the nanoscale




High-resolution image of an uncoated biological                    Array of 5 (±1) nm nanopores in Si3N4 membrane.                    Array of Pt nano-pillars (35 nm diameter & 50 nm
sample showing virus particles attached to a cell.                 A 10 x 10 array can be created in under one minute.                pitch) deposited using the helium ion beam.




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  ALSO AVAILABLE TO READ:
    Journal section magazines highlighting the
best content in three of Nanotechnology’s subjects


                  NaNotechNology
                  Biology and medicine
                  Image left: Nerve cell morphology after co-culture for 22 days.
                  Wei-Chin Huang, Jiunn-Der Liao, Chou-Ching K Lin and
                  Ming-Shaung Ju 2011 Nanotechnology 22 275101.




                  NaNotechNology
                  Sensing and actuating
                  Image left: A bright field image of a Pseudopediastrum colony using
                  an optical microscope. D B Phillips, J A Grieve, S N Olof, S J Kocher,
                  R Bowman, M J Padgett, M J Miles and D M Carberry 2011
                  Nanotechnology 22 285503.




                  NaNotechNology
                  Energy at the nanoscale
                  Image left: Freestanding Si nanospheres prepared from the gas phase
                  and subsequently stain etched. Bernhard Goller, Dmitry Kovalev and
                  Olga Sreseli 2011 Nanotechnology 22 305402.




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