SUPERCONDUCTIVITY by keralaguest

VIEWS: 11 PAGES: 9

									AREA 2. - SUPERCONDUCTIVITY

Activity 2.1 Non equilibrium superconducitivity and sensors
A. Barone, N. Marrocco, L. Parlato, G. Peluso, G. Pepe, A. Ruosi, M. Valentino

The research activity, during 2004, was focused on the investigation of the role of different
materials and/or configurations for fast sensors based on superconducting tunnel junctions.
In particular, we have devoted our attention to investigate superconducting structures under
optical irradiation. Indeed, the high energy resolution (a few eV for 6-keV X-ray) and the
intrinsically short response time (down to few ps) of these sensors are very interesting
together to the development of superconductive digital electronics, based on the processing
of single magnetic flux quanta (Rapid Single Flux Quantum), capable of operating at clock
frequency in excess of 100 Ghz. We have studied the physical properties of new materials
to be considered within the framework of low temperature detection. These properties
depend on the relaxation processes involving phonons, quasiparticles and Cooper pairs
during the energy cascade following the absorption of radiation. The energy down
conversion processes are related to the electron-phonon scattering strength e-ph that is
usually expressed in terms of the electron-phonon coupling time, 0, which is
characteristic for each material. In the framework of the McMillan model for the
superconducting critical temperature Tc within the Debye approximation we have
estimated 0 for different superconductors. The obtained values for 0 are discussed for new
possibilities of unexplored materials in the field of superconducting detectors. Reflectivity
measurements of superconducting films by pump and probe techniques with femtosecond
laser source, recently implemented in our laboratory, allows to evaluate also the
characteristic time of the materials. In particular we have evaluated the characteristic time
for superconducting/ferromagnetic (Nb/NiCu) bilayers obtaining informations about the
proximity effect at the surface S/F in according to the tunnel spectroscopy in S/F-I-S tunnel
junctions. The combination of a conventional superconducting material (e.g Nb, al, etc.) in
close proximity to a ferromagnetic layer can result in a S/F type structure showing
superconducting and normal electronic properties at the free surfaces of the bilayer,
respectively. This allows to use very thin films as trapping layers compatible with standard
fabrication procedures in VHUV systems. The research activity is focused on the
fabrication and characterization of tunnel devices in which one electrode is a S/F bilayer.
We have chosen an alloy of Ni and Cu with equal concentration of either Ni and Cu and an
alloy of Ni and Pd with different concentration. Josephson tunnel junction with this type of
S/F bilayer have been fabricated on micron scale by using a standard photolithographic
process already employed in superconducting electronic technology. Multilayers have been
deposited by dc-sputtering in ultra-high vacuum system (UHV). The proximity effect at the
interface has been studied, varying the thicknesses, by tunnel spectroscopy. Experimental
results were compared to a microscopic S/F proximity model obtained by a fully self –
consistent numerical procedure employed in solving the Usadel equations at arbitrary
values of the F-layer thickness, magnetization and interface parameters. In collaboration
with l’Ecole Duperieure de physique et Chimie Industrielle (ESPCI) of Paris three-
terminal superconducting devices with Al/NiPd as one electrode have been fabricated and
characterized. This device is very promising both as transistor or superconducting sensor
and to investigate the non equilibrium processes in the common electrode. Tunnel
spectroscopy measurements have been realized in a He3 cryostat down to 300mK, also in
presence of a magnetic field. In particular, the tunnel conductance variation of each
junction of stack has been measured in presence of an injected stationary current in the
other. The experimental data have been analysed using a thermal model. The analysis of
dynamics of the electronic excitations, in non-equilibrium regime, in the bilayer has

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shown, in the structures fabricated, a tunnel conductance value lower with respect to the
thermal one. As a consequence, the probability that the excess charge, created in the
common electrode, tunnel through the second barrier rather than to interact with the
thermal fonons is quite low. Moreover, the measurements show, due to the presence of the
magnetic layer in the vertical structure that breaks off, in same sense, the simmetry of the
system, in the detector junction response an high degree of directionality very useful for
applications of this type of structure as a transistor–like device.
Moreover, many effort has been spent to study experimental and theoretical issues related
to SQUID magnetometry. The research activity concerning the EU project DIGI SQUID
has been focused on the design of the measuring head of the Non Destructive Testing
system for the aerospace applications. The new NDT system will be based on the digital
HTS SQUID magnetometer e/o gradiometer working in unshielded environment and
cooled using a cryo-cooler. The NDT prototype SQUID based has been designed to detect
very deep defect in metallic alloy such those usually used in the aerospace industry.
The research activity in the framework of the MIUR project “Analisi non distuttive su
materiali compositi strutturali per l’industria aeronautica” has been focused on the
development of the HTC SQUID based NDT system dedicated to the analysis of the
damage in composite material like Carbon Fibre Reinforced Plastic (CFRP) and Fabric
Metallic Laminate (FML). The aim of this activity using the NDT SQUID system, was the
detection of the impact damaged in the composite material. Other research activity has
been followed concerning the development of the software for the 2-D magnetic image,
the acquisition data system and the design of the non-magnetic stress device to test the
composite sample.

Program for 2005
The research activity during 2005 will focus on the investigation of the role of the
interaction between electromagnetic, in particular optical, radiation and superconductive
systems. Such devices could be used both as single photon detectors, and as very fast
optical packed detectors.
The research will be devoted on the theoretical and experimental study of the fast
relaxation processes in thin superconducting films and/or in hybrid hetero-structures by
using a pump-probe technique with a high time resolution (<100 fs) at low temperatures..
Then, we will focus our attention on the fabrication and the investigation of
superconducting tunnel junctions in which one or both electrodes are S/F bilayers. Three-
terminal superconducting junctions in planar configuration will be realized. The electronic
characterization of devices will be performed in locally shielded environments by using a
low noise electronics. Moreover, the fabrication of the superconducting devices grown on
crystals with electro-optical (E0) properties, will be realized.
Research activity will be also focused on the optimization of the NDT system. New
gradiometric and absolute excitation coils and non-magnetic x-y position stage for the
positioning of the excitation coil under the cryo-cooler will be designed and realized. The
digital SQUID electronics equipment will be tested and employed on the test sample to
validate the digital NDT system.
The forward electromagnetic problem concerning the test sample and the SQUID
gradiometer will be studied using Volume Integral Method (VIM).
Research activity will be also devoted to the correlation between the mechanical stress and
magnetic signal with the aim to study the damage in the early stage in composite material,
the measurements of electrical conductivity properties of composite material under
mechanical load compression and the detection of the ongoing mechanical stress of CFRP

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composite. HTS SQUID planar gradiometer and other magnetic sensor will be employed
for the detection of damage and of ongoing corrosion in FML composite.


Activity 2.2 - Josephson structures for fundamental studies
A. Barone, D. Born, D. Dalena, E.Gambale, R. Latempa, G. Peluso, G. Pepe, A.Ruotolo, D. Stornaioulo, F.
Tafuri

During 2004, using an optical system based on a femtosecond pulsed laser with energy of
about 10nJ for pulse and rate of approximately 80 MHz, set-up in laboratories of the
Department, non-equilibrium measurements on superconductive structures both in
stationary and non stationary conditions have been carried out.
Non-stationary measurements have been carried out by means of pump and probe
technique in order obtaining from reflectivity values information on the relaxation times
of superconductive materials or hybrid structures constituted from bilayers S/F.. Results in
agreement with those reported from tunnel measuresments have been obtained for
relaxation times of bilayers Nb/NiCu. Preliminary trials of fabrication and measurement of
spin-vale superconducting devices based on Giant Magnetoresistance (GMR) effect have
been carried out. The configuration under investigation was an S/F1-I-F2/S structure where
the superconductor S was Niobium (Nb) whereas the two ferromagnetic layers were two
solid solutions of Nichel (Ni) and Copper (Cu) with different concentrations. The grown
films were characterized by Energy Dispersive Spectroscopy (EDS) and X-ray
diffractometry (XRD). Electrical characterizations were carried out by measuring the
resistivity in a large range of temperatures and for different stechiometric compositions.
Since the magnetic properties of the NiCu films depend on the thickness of the film itself,
besides the concentration of the two elements, a systematic study on the changing of these
properties with the thickness has been carried out. The study led to the discovery of a
strong perpendicular magnetic anisotropy never observed in this kind of alloys and of great
interest for the industry of the hard disk mass memories.
In stationary conditions grain boundary Josephson junctions based on the technology of the
YBCO have been irradiated. The relaxation time value of the YBCO in reasonable
agreement with those reported in the literature has been obtained from preliminary
measurements on these structures
 Grain boundary junctions are based on the unique property that two grains with different
orientations may generate Josephson coupling and represent at the moment the most
reliable structures for both applications and fundamental experiments. Progress in the
reproducibility of their properties and in the understanding of some major features has
been steadily registered. Within this framework the biepitaxial junctions based on the
YBa2Cu3O7 (YBCO) compound and realized at the University of Napoli are extremely
promising due to their good properties and their versatility. Biepitaxial junctions are based
on the use of a seed layer able to determine a growth on itself different from the one on the
bare substrate. Such junctions exhibit highly reproducible properties and allow the
realization of whatever kind of geometry differently from bicrystalline junctions, which are
constrained by the substrates. Recently, as also discussed in the following, we have shown
for the first time macroscopic quantum effects in HTS Josephson junctions. This represents
the first real step toward a possibile implementation of these junctions for pi-circuitry.

Recently we have mostly focussed on structures employing (110) SrTiO3 as a substrate
and CeO2 as seed layer. Different types of grain boundaries can be obtained by exploiting
the (103) anisotropic growth and an opportune definition of the seed layer geometry. It has
been demonstrated the possibility to tailor the critical current density (J C) and the normal
state resistance by varying the seed layer interface angle with respect to electrodes.
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The use of a CeO2 as a seed layer determines a complicate grain boundary configuration,
that can be seen as a result of two rotations: a 45° [100] tilt or twist followed by a 45° tilt
around the c-axis of the [001] film. For this junction configuration a d-wave order
parameter symmetry would determine junction with a natural intrinsic -shift in the phase
and, in opportune configurations, -loops, which are of great interest for fundamental
studies and applications. Such loops are probably due to the nature of the order parameter
and manifest as fractional vortices originating a puzzling phenomenology. Current vs
voltage (I-V) characteristics as a function of the magnetic field (H) showed an high quality
of the realized devices. Measurements have been extended to low temperatures to study
mesoscopic quantum effects and in view of quantum coherence measurements to be
performed at even lower temperatures (such measurements have been partly realized and
will be realized in the future in collaboration with Chalmers University (Sweden)).
The anomalous tranport properties have been confirmed by two different types of
measurements: 1) standard transport measurements; 2) Scanning SQUID Microscopy
(SSM), able to detect magnetic features induced by an external magnetic field or even
spontaneous. The formers mainly consist of anisotropy measurements and showed an
oscillatory dependence of the critical current density as a function of the angle. This is the
first experiment that demonstrates d-wave induced effects in an all HTS structure in a
simple junction geometry different from the rings used for all the previous experiments.
We have also studied the half flux quantum related to -loops through novel techniques
and in particular Scanning SQUID Microscopy and RF techniques. Such studies have been
carried out in collaboration with IBM T.J. Watson Research Center , Yorktown , NY
(USA)


Program for 2005

During 2005 the research activity will be focused on the study of the optical response in
stationary and fast regime of new materials including HTC superconductors. The
characterization of S/F type bilayers, from the point of view of the their non equilibrium
property, will continue.
The preliminary results achieved on S/F1-I-F2/S structures show that, the fabrication of
devices on nanometer scale is needed. A process based on Focused Ion Beam (FIB)
lithography technique will be set up.. The possibility of growing the multilayers without
breaking vacuum will be fully exploited to obtain very high quality interfaces.
A dc-magnetoresistance measurement system, based on helmoltz coils, completely
automatized with dedicated software,.will be set up.
Josephson junctions based on HTC superconductors will be studied from the non-
equilibrium point of view by means of both irradiation in continuous or pulsed regime.

We first aim to optimize the junctions fabrication process in a system completely dedicated
to the junctions realization. This should improve the uniformity and the yield of the
junctions also in view of possible implementation of these junction for quantum circuitry.
The possibility to obtain a qubit seems to be “favoured” by the existence in such systems
of a doubly degenerate ground state, determined by a d-wave order parametr symmetry and
time reversal symmetry breaking.
To this aim a systematic analysis of this type of biepitaxial junctions is required along
with a comparison with traditional biepitaxials. It is important to study the feasibility of
circuits based on both “0” e  junctions. These can be realized by using different seed
layers in the biepitaxial technique. Besides the standard characterization in a wide
temperature range (from 4.2 K to 300 K) and along different directions, we will

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investigate the behavior of submicron junctions down to 300 mK, employing an Helium 3
system. Low temperature measurements in presence of magnetic field could allow to study
mesoscopic effects in such junctions.


Activity 2.3 Electrodinamic properties of innovative materials and metamaterials
   A. Andreone, M. Aurino,G. Cifariello, E. Di Gennaro, G. Lamura, M. R. Masullo*

     MATERIALS
Activity has been mainly devoted to the characterisation of linear and non linear
electrodynamic properties of low, medium and high critical temperature superconductors.
In particular, it has been focused on the following fields:
i) linear electrodynamic properties: the London penetration depth L as a function of the
temperature has been studied on YBa2Cu4O8 (Y124) single crystals by using a high-
resolution mutual inductance technique. Y124 is a stoichiometric compound characterized
by a double CuO chain per unit cell acting as charge reservoir and by the absence of any
disorder or structural inhomogeneities arising from chemical substitutions and/or oxygen
vacancies. The experimental data show, in the low temperature region down to 4.2 K, a
marked linear dependence of the variation of the in plane magnetic penetration depth that
confirms the existence of zero-energy thermally activated excitations. The experimental
results give important informations on the role of the proximity coupling between
superconducting planes CuO2 and metallic chains CuO on the low energy excitation
spectrum of this system. These samples have been provided by the Solid state Laboratory
of ETH in Zurich, Switzerland.
ii) high frequency (GHz) non linear electrodynamic response: measurements of the
intrinsic non linear response (Non Linear Meissner Effect) in superconductors make
possible to study the symmetry of the gap function (k). This is done by measuring the
temperature behaviour of the intermodulation products (IMD) in the microwave region. To
achieve this goal an open-ended dielectric single-crystal sapphire puck resonator has been
set up. This cavity has a TE011 mode resonant frequency of 6.7 GHz and an unloaded
quality factor higher than 105 at 4.2 K. The experimental data show a marked different
temperature behaviour of IMD in the case of s-wave superconductors (Nb films) and d-
wave superconductors (YB2C3O7-films) respectively. This technique has been applied to
the new superconductor MgB2 and the experimental results confirm the s-wave nature of
the order parameter for this system. The Nb films have been provided by the CEA in
Grenoble and by the CNR in Arco Felice (Naples). The MgB2 films have been obtained
thanks to a collaboration with the Department of Physics of the Penn State University,
Pennsylvania, (U.S.A.).
iii) low frequency non linear response (kHz): the critical current density of a
superconductor can be easily determined by measuring the behaviour of the third harmonic
response at low frequency (1 kHz) using an inductive and contactless method. Driving a
sinusoidal current in a single coil placed in front of a superconducting sample, a non zero
third harmonic voltage is induced in it when the sample goes beyond the Bean critical
state. To take into account the magnetic coupling between the sample and the coil it has
been developed a discrete model that is a more realistic representation of the inducing and
induced currents distribution. In the framework of this model the coefficients linking the
current flowing in the coil and the critical current density of superconducting thin films
have been calculated. By using these new results the critical current density on standard
YBCO thin films of known transport properties has been succesfully reproduced.

METAMATERIALS

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In 2004, research in this field has been aimed to the understanding of the electrodynamic
response of new types of metamaterials.
Mainly, the activity has been focused on two different structures:
(i) a photonic band gap (PBG) based monomodal cavity, for the possible use as basic
element in particle accelerators for nuclear and biomedical applications
(ii) a matrix of metallic and ferromagnetic microwires, to study its properties of
metamaterial having a negative effective dielectric constant over a suitable frequency
range
This work is done in collaboration with the Naples INFN Unit, as for the development of
accelerating PBG cavities, and with the group of Physics of Accelerators of the University
of Naples and the Northeastern University of Boston, as for the study of the properties of
negative refraction in photonic crystals (PCs) and plasmonic mesostructures.
Specifically, in the laboratories of the Physics Department of the University of Naples e.m.
simulations and experiments on metallic arrays of Cu-Be microwires (dia 75 m) placed in
guided structures have been carried out. The aim of this study is to investigate the
electrodynamic response of these metamaterials as a function of relevant geometrical
terms, like wire diameter, lattice parameter, guide height. Measurements clearly show that
there is a 105 reduction of the plasma frequency of the mesostructure, in respect to the bulk
metal.
Realisation of plasmonic structures made of “dilute” metals may lead to applications in the
field of microwave components, such as high pass filters or highly directive antennas.


Program for 2005

MATERIALS
Main activity will be devoted to the electrodynamic characterisation of high, medium and
low critical temperature superconductors and to the study at low temperatures and high
magnetic fields of manganites thin films. In particular the focus will be on the following
research fields:
a) study of the order parameter symmetry in single crystals of high critical temperature
    superconductor by using the IMD technique previously set up;
b) measurement of the microwave surface impedance of MgB2 thin films versus
    temperature and dc field, in order to study the effect of the double gap nature of this
    compound on the flux dynamics in the mixed state;
c) measurements of the magnetic penetration depth of electron doped cuprate samples as a
    function of the doping level by using a high resolution inductive technique at 4 MHz;
d) study of the interplay between magnetism and superoconductivity by measuring the
    magnetic penetration depth in copper oxide compounds of the family RCeCuO where
    R Nd3+ or Sm3+ that are ions on non zero total magnetic moment;
e) study of the magnetotransport properties of manganite thin films at low temperature
    and high magnetic fields, as a function of the doping level and thickness of the
    samples.

METAMATERIALS
We will continue working on the full electromagnetic characterisation of plasmonic
metallic arrays, varying the wire diameter, the lattice parameter, the height of the guided
structure. The study will be extended to arrays made of ferromagnetic (a Co-Fe-Si-B alloy)
and superconducting (Nb and Nb-Ti) microwires.
As for the research on photonic crystals, we will focus on the thickness dependence of the
wave propagation inside the PCs (Pendellösung phenomenon).

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Activity 2.4 . Properties of oxides and superconductive materials
M.Barra, A.Cassinese, F. Chiarella, R.Di Capua*, F.Miletto*, A. Prigiobbo, M.Salluzzo*, U.Scotti di
Uccio*, R.Vaglio

A relevant experimental effort has been dedicated to analyzing the structural,
morphological and electronic properties of epitaxial La0.67Sr0.33MnO3 thin films. We
resorted for our investigation to a wide number of experimental techniques, including X-
ray reciprocal space mapping, acquisition of R(T) curves, Rutherford backscattering,
vibrating sample magnetometry, AFM and STM topography and collection of conductance
maps by STM that evidentiated the presence of spatial electronic inhomogeneities at room
temperature, which can be described in the frame of the phase separation theories
introduced for the manganites compounds.. Interesting results have been achieved in
analysing the effects of strain and disorder, which seem to be responsible for the variety of
different electronic behaviours observed in manganite samples.

Field effect measurements on ultrathin Nd1+xBa2-xCu3O7 films have been performed. An
insulating to superconducting transition induced by the electric field is observed for the
first time. Insulating films behaves as 2D-Mott insulators, where the holes are localized.
We have demonstrated that the localization length d can be tuned by electric field effect. In
particular d increases by injecting holes in the sample and becomes of the order of the
coherence length (or larger) when the sample undergoes the insulating to superconducting
transition induced by field effect .
A study of the role of strain on the transport properties of ultrathin Nd1+xBa2-xCu3O7 films
growing samples on (100) SrTiO3 substrates characterized by a thickness varyng from 120
to 4 unit cells has been carried out. A superconducting-insulating transition by decreasing
the thickness from 10 to 8 unit cells and a structural transition from a pseudotetragonal to a
tetragonal structure at about 20 u.c. correlated with a Tc decrease has been observed. A
further structural transition occurring at 60 u.c. from pseudotetragonal to an orthorhombic
phase does not affect the transport properties of these films.

Accurate surface diffraction measurements on SrTiO3 single crystals characterized by
various surface terminations due to different chemical and thermal treatments have been
performed. The surfaces are 2x2 reconstructed. For each sample we measured the whole
profile of the integer CTR (Crystal Truncation Rods) and of the fractional rods associated
to the surface reconstruction.

Tunnelling spectroscopy measurements have been realised on the new superconductor
MgB2 by a cryogenic Scanning Tunnelling Microscope (STM), in magnetic field and at
several temperatures. The experiments were performed on both bulk polycrystalline and
thin films samples, and on as-grown, Al-doped, or neutron irradiated samples. The aim of
the research is to study the effects of disorder on MgB2 superconducting properties, in
particular on the critical fields and on the gap.
The studies on microwave applications of high Tc superconductors have been completed.
New configurations of miniaturized fracta filters have been designed realized and tested. In
cooperation with the University of Rome “Tor Vergata” a front-end receiver with an
integrated filter and low-noise cryogenic amplifier has been realized and tested. Finally a
theoretical study on the anomalous behavior of superconductors close to the transitino
temperature has been carried out.



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Program for 2005

The experimental activity in year 2005 will be mostly dedicated to setting up and
exploiting the potential our new advanced deposition and characterization system for
epitaxial oxide thin films. The new apparatus named “MODA” should allow to strongly
enhance the impact of our research on manganites, cuprates and other oxides. The
coexistence of different electronic states on La0.7Sr0.3MnO3 thin films will be further
studied by scanning tunnelling spectroscopy measurements. In particular, a deep analysis
of tunnel spectra collected in regions with different spectroscopic signatures will be
provided, a more detailed study of electronic unhomogeneities will be performed, and the
temperature behaviour of such unhomogeneities will be studied.

The study of ultrathin film of Nd1+xBa2 xCu3Oz, will be continued. Additional accurate
conventional X ray diffraction measurements and synchrotron radiation experiments will
be performed. Moreover Hall and Seebeck effect measurements in function of the film
thickness wil be done in order to determine the change of the number of carriers in
function of the film thickness and correlate them with the structural change and transport
properties. Moreover the modification of density of state associated to the CuO2 planes and
CuO chains will be investigated by RIXS (Resonant inelastic X-ray scattering) on thin
films having different number of layers [HE1737 Experiment at the ESRF to be held in
June 2005]. Finally electric field effect doping experiment will be performed on
Nd1+xBa2-xCu3Oz as well as artificial superconducting BaCuO2/CaCuO2/BaCuO2 structures.

The study on the effects of disorder in MgB2 will be continued with STM/STS
measurements on neutron irradiated thin films. The experimental results will be compared
with previous results obtained inside the present research, in previous researches and in
studies from scientific literature, in order to fully characterise the changes introduced by
the irradiation process on this compound, MgB2, on which different sources of disorder can
produce very different effects because of its peculiar electronic structure An activity of
realization and characterization of Zn films of different thicknesses for Casimir cavities
will be finally started .


Activity 2.5 - Characterization of materials and oranic devices
M.Barra, A.Cassinese, F. Chiarella, R.Di Capua, A: Priggiobbo ,R. Vaglio

In the 2004 a new activity concerning the investigation of the electrical transport property
of the organic and hybrid organic/inorganic materials of interest for the realization of non
convential electronic and optoelectronic devices has been started. Such research goes Is
srongly related to that regarding oxides having with it many affinities and various
complementarities aspects both for studies of basic physics and possible applications.
One of their most common interesting features is the possibility to modify the electronic
properties by modulating the charge carrier density, and, this can be done in an efficient,
reversible and non destructive way by fabricating field effect (FET) devices.

1) In this first year an appropriate experimental setup allowing the electronic
measurements, of organic and hybrid materials has been equipped. The apparatus allows
the possibility to carry out electrical characterizations in atmosphere controlled (regarding
gases and luminosity) and by using not destructive techniques thanks to an opportune
probe station equipped for the measurements on organic materials. Moreover a system



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deposition allowing the realization of in situ organic and inorganic multilayers based on
techniques of evaporation and sputtering d.c. and r.f. has been equipped.

2) In collaboration with the ENEA reserc center of Portici, Organic films of
polivincarbazolo (Pvk) of interest for the realization of organic LED and material organic
hybrids have been characterized. The resistance as a function of the temperature and film
thickness have been measure and the electrical mobility of the carrier has been measured
by realizing of opportune field effect devices.

3) Hybrid films, composed from perovskiti and ammines, (CH3NH3)MX3 with M=Sn, Cu
and X=Cl, Br, and realized by CNR-IMEM of Parma, have been investigated. For these
materials a preliminary study of the transport properties by varying stechiometry of the
compound, the film thickness and the substrate has been carried out.

4) The realization of regular submicormetric structures has been realized by considering
nanoporouse membranes. The electrical properties of the array have been studied by
varying the temperature and by realizing field effect devices observing different
mechanisms of conduction (metallic or insulating like)


Program for 2005

1) The up grade of the experimental set –up will be completed including AC
   measurements and dielectric constant measurements as well as different field effect
   geometries obtained with various barrier insulating materials too, will be investigated.
   Moreover, a definition of the electrical contacts with a nanometric resolution, obtained
   through electron beam litography, will be carried out.
2) A systematic investigation of the PVK film, to single layer and double layer O-LED,
   PVK and Alq3by based , will be performed , in controlled atmosphere, by varying the
   deposition parameters and the temperature.
3) Efforts will be dedicated to the electrical characterization of hybrid films focusing the
   attention on (CH3NH3)MX3 with M=Sn and X=Cl, Br compounds. The electrical
   resistance and the mobility carrier will be measured as a function of the temperature.
4) The electrical properties of others conducting organic materials such as rubrene and
   polithiophene will be investigated. The rubrene films will be realized through spin
   coating and evaporation techinique, while the second ones, having an innovative
   stechiometric formulas, will be realized by the Chemical Departments by spin coating
   techniques. The polithiophenes will be doped through Iodine and/or ClFe3 in order to
   obtain hybrid materials of interest for the FET realization.
5) STM measurements, both topographic and spectroscopic, will be performed on carbon
   nanoparticles produced by flame combustion. The study of pollutant products of
   combustion, having a size of few nanometers, has been up to now very limited, since
   the conventional characterization techniques did not allow a deep investigation on
   them. STM can be a suitable tool for this research, which would be of great toxicologic
   and environmental interest and impact. Moreover the possibility to realize
   measurements on conductive organic films (such as rubrene, pentacene, politiophene,
   pvk) for a better understanding of the physics mechanisms of the electrical conduction
   in these materials will be performed too. A possible field of interest should be the
   investigation of the trap state and their influence on the conducting performances .



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