Nanocrystals of Metal Atoms Passivated by Self-Assembled

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					Nanocrystals of Metal
Atoms Passivated by Self-
Assembled Monolayers

Dr. Srihari Murthy
Professor in Nanotechnology
PSG Institute of Advanced Studies
Coimbatore
Topics

 Nanocrystal Gold Molecules
 Thiol-Derivatized Silver Nanocrystals
 Digestive Ripening (Ken Klabunde)
 Nanoparticle Extended Materials
 Optical Studies
 Application in Life Sciences (Chad
  Mirkin)
Nanocrystal Gold Molecules

 Motivation
 Preparative Methods
 Characterization
 Saga of the One-Phase Synthesis of
  Thiol-Derivatized Gold Nanocrystals
 Current Status
 Future Directions
Inspiration from the Fullerenes
        C60                         C70
                                                             C60 and C70 were
                                                              discovered in Rick
                                                              Smalley’s Lab at Rice
                                                              University
(Images’ Source: http://www.chem.sunysb.edu/                 They represented a new
msl/fullerene.html)
                                                              form of carbon distinct
                                                              from diamond and
                                                              graphite
                                                             Bulk Synthesis
                                                              subsequently developed
                                                              by Huffman and
                                                              Kratschmer
 (Mass Spectrum courtesy of Craig Watson, Virginia Tech;
 source: http://elchem.kaist.ac.kr/vt/chem-ed/ms/tof.htm)
Research Challenge in
Nanomaterials
“The creation of perfect nanometer-scale
crystallites (nanocrystals), identically
replicated in unlimited quantities, in a state
that can be manipulated and understood
as pure macromolecular substances, is an
ultimate challenge of modern materials
research with outstanding fundamental and
potential technological consequences.”
(1. J. Mater. Res. 1989 4 704; 2. Adv. Mater. 1996 8 428)
Implications
 For the Materials to be Synthesized
     Size and Morphologically Specific
      Nanocrystals
        CompositionallySpecific
        Behave like Macromolecules

 Why Important?
     Properties Likely to be Precisely Controlled
        Provide ability to accurately model properties
         and phenomena quantitatively
        Highly Reliable Technological Properties
   Cluster Beam Mass Spectra

                                                   Large Magic Number
                                                    Clusters are
                                                    Observed
                                                   Here Magic Numbers
                                                    Correspond to
                                                    Icosahedral Clusters
                                                    of Atoms
                                                   They are Purported
                                                    to be Especially
(Image Source: T.P. Martin, Physics Reports 273     Stable Arrangements
(1996) 199-241)
                                                    of Atoms
Comparison With C60
 C60 Molecules are Stable Against Coalescence
      They are Self-Closing Structures
      Hence, They can be Isolated in Bulk Quantities


 The Inorganic Nanocrystals of Interest are not
  Stable Against Coalescence
      These Nanocrystals Need to be Surface
       Derivatized (Passivated)
      Only Then, Can They be Isolated in Bulk Quantities
Requirements of the Passivant

 Number of Molecules of the Passivant
  that Passivates a Nanocrystal of a
  Particular Characteristic Has to be Fixed

 This can Lead to Nanocrystal Molecules
  of the Form:
                 (A)N(P)M
Proposed Material System

 Material Making up the Nanocrystal
  Core:
              Gold
 Passivating Molecules:
            Long Chain
            Alkane Thiols
 Proposal Made by R. L. Whetten
      Why This System?

                                                       Long Chain Alkane
                                                        Thiols are Konown to
                                                        Form Self-
                                                        Assembled Mono-
                                                        layers on Gold
                                                        Surfaces
                                                       These SAMS do not
                                                        Modify the Gold
(Image Source: http://www.ifm.liu.se/applphys/ftir/
sams.html)                                              Surface Crystall-
                                                        ography
   Proposed Method of Whetten
                                                    Nanocrystals to be
                                                     prepared in an Aerosol
                                                     Flow Reactor by
                                                     Condensation
                                                    Can be Annealed if
                                                     Required
                                                    Passivation can be
                                                     Achieved, if necessary,
                                                     by Passing the NCs
                                                     through a Solution
                                                     Containing the Passivant
(Alvarez et al, J. Aerosol Sci. 1998 26 115-127)     of Interest
                Method of Brust and Co-
                Workers
                                                            Two Phase Liquid-Liquid
                                                             System of Water and
                                                             Touluene
                                                            Tetraoctylammonium
                                                             bromide is used to
                                                             transfer AuCl4- into
                                                             Toluene
                                                            Soduim Borohydride
(Brust et al, J. Chem. Soc., Chem. Commun. 1994 801-802)
                                                             supplies Electrons
                                                            Reduction of Au ions
                                                             done in the presence of
                                                             Dodecanethiol
                Nature of Material Prepared
                                                            TEM shows Crystalline
                                                             Core With a Broad
                                                             Distribution of Particle
                                                             Sizes
                                                            IR Spectra Provides
                                                             Evidence for Surface
                                                             Derivatization
                                                            The Material Can be
                                                             Precipitatated from
                                                             Toluene and Re-
                                                             Solubilized Without
                                                             Change in Chemical
                                                             Composition
(Brust et al, J. Chem. Soc., Chem. Commun. 1994 801-802)
Implications For Our Work
                Examine if the Broad
                 Distribution
                 Contained a
                 Sequence of
                 Nanocrystal Gold
                 Molecules
                Our Study was
                 reported in Advanced
                 Materials
                Forms the 12th most
                 Cited Paper in the
                 field of Nanocrystals
                 in the World
Size-Selective Precipitation

                 Controlled Addition
                  of Miscible Non-
                  Solvent
                 Heavier Fractions
                  Precipitated Earlier
                 Isolated Fractions
                  Characterized by
                  Laser Desorption
                  High Mass
                  Spectrometry
  Mass Spectrometry: The
  Technique Developed
                                              Ablation by Either the
                                               Second Harmonic of a
                                               Nd:YAG Laser (532 nm,
                                               unfocussed) or an XeCl
                                               excimer Laser (308 nm,
                                               weakly focussed)
                                              Allowed to pass through
                                               a TOF Region
                                              Detected
(Image Source: Z. Phys. D 1997 40 147-151)
Mass Spectrometry:
Observations and Analysis
                                          The as prepared material
                                           shows a broad mass
                                           spectrum
                                          Fractionated material
                                           reveals distinct peaks the
                                           masses of which correspond
                                           with a series of Truncated
                                           Octahedral Nanocrystals
                                          What does this tell us about
                                           the NC cores of the
                                           separated fractions?
                                          Cluster Perfection may be
                                           Taking Place during the
                                           Laser Ablation Process

(Image Source: Adv. Mater. 1996 8 428)
Results From TEM
                                          It is Possible to Find
                                           Some NCs Whose HR
                                           Images Correspond to
                                           Projections of
                                           Compositionally Specific
                                           TO+ Structures
                                          2D Arrays of NCs Show
                                           Size Uniformity
                                          Obtaining Series of HR
                                           Images of NCs
                                           Prevented Due to
                                           Random Orientations of
                                           NCs on the Amorphous
(Image Source: Adv. Mater. 1996 8 428)
                                           Carbon Substrate
Results From XRD

                                           Small Angle Pattern
                                            Indexes to a bcc
                                            Lattice
                                                This is Interesting
                                           Large Angle
                                                Twinned NCs give a Fit
                                                 Across the Pattern-This
                                                 is Remarkable
                                                How Sensitive to
                                                 Shape Variations
                                                 Still Needs to be
 (Image Source: Adv. Mater. 1996 8 428)          Examined
One Liquid-Phase Synthesis

 The Method of Brust et al involves two Liquid
  Phases
 I Felt Why Should We Not Reduce the Metal
  Ion in a Phase in Which the Reducing Agent
  and the Capping Agent are Also Soluble in
 This Led to Our Developing the One Liquid-
  Phase Method Using Ethanol as the Liquid-
  Phase
 We Implemented this Method Successfully for
  Gold and Silver
Thiol-Derivatized Gold
Nanocrystals: Mass Spectrometric
Results
                 Varied the Gold:Thiol
                  Ratio
                 See a Single Magic
                  Number Nanocrystal
                  Species
                 Question:
                      Is Our Synthesis
                       Yielding a Magic
                       Number Species?
                      Is Perfection Taking
                       Place During Laser
                       Ablation?
TEM Results

               Shows Variation in
                Particle Size
                Distribution as the
                Thiol-Gold Ratio is
                Changed
HRTEM of Closed Packed
Regions
              Both Size and
               Morphological Variation is
               There
              Hence the Observed Magic
               Number Nanocrystal in the
               Mass Spectrometric
               Experiments is Due to
               Perfection in the Laser
               Ablation Process
              However, There is
               Something Special About
               the 30 kamu Cluster- The
               Meaning of Which Has Yet
               Got to be Worked Out
Structural Characterization:
Where are We?
 We Still Need a Method For Determining
 the Morphological Specificity of
 Nanocrystals with Atomic-Scale Detail
 In the Previous Slide We Saw HRTEM
 Results which Showed Resolved Lattice
 Planes Only for Certain Orientations of
 the Nanocrystals
     This is because of the Limitation of the
      Resolution of the Microscope Used
Is High-Resolution Lattice
Imaging the Answer?
 Suppose We have a Microscope Which
  Has 0.1 nm Resolution or Better, Can
  We Devise a Method for Determining the
  Morphology of Nanocrystals with Atomic-
  Scale Detail?
 Resolution of 0.1 nm Possible with High-
  Resolution Electron Holography
How Does This Method Work?
              Take Lattice Images of
               the Nanocrystal in
               Different Crystallographic
               Orientations
              Do Computer Simulations
               Using a Particular
               Nanocrystal Model to
               Match the Obtained
               Experimental Images
              The Nanocrystal Model
               that Provides the Best
               Match is Then The
               Obtained Species
Scope for Further Research

 Would Like to Use Multi-Slice Imaging
  Theory to Computationally Determine
  How Sensitive This Method is to
  Variation in Atomic-Scale Detail
 Collect Nanocrystals From the Laser
  Ablated Ion Beam on Suitable
  Substrates and do High-Resolution
  TEM/Electron Holography on Them
Thiol-Derivatized Silver
Nanocrystals: Evidence For
Crystalline Silver Core
Evidence For Surface
Passivation
 The Cleaned Solid Material Can be Repeatedly
  Precipitated and Resolubilized in Nonpolar
  Solvents Such as Hexane and Toluene
 It Cannot be Solubilized/Dispersed in Polar
  Solvents Such as Water and Ethanol
 Silver Nanocrystal Cores do not Touch each
  Other in Densely Packed Regions as Seen by
  TEM
 EDS Spectrum of the Material Shows Peaks
  Corresponding to Carbon, Sulfur and Silver
Implications

 These Results are Consistent with the
  Synthesized Material being a
  Dodecanethiol-derivatized Silver
  Nanocrystla Material with a Mean
  Crystalline Silver Core of 3.1 +/- 0.6 nm
 The Stage is Set for Conducting Size-
  Specific Studies in These System
           Digestive Ripening (Ken
           Klabunde)
                                                  Prepare Thiol-
                                                   Derivatized Au
                                                   Nanocrystals
                                                  Heating Under
                                                   Reflux of Toluene
                                                   Containing Thiol-
                                                   Derivatized Au
                                                   Nanocrystals
(Source: J. Am. Chem. Soc. 2002 124 2305-2311)
TEM Results
     BEFORE                              AFTER




(Source of Images: Langmuir 2002 18 7515-7520)
   Nanocrystal Arrays

                                                      First to Report that
                                                      Size-Selected Thiol-
                                                      Derivatized Nano-
      (Image Source: Adv. Mater. 1996 8 428)          crystals Formed
                                                      Highly Ordered Two
                                                      Dimensional and
                                                      Three Dimensional
                                                      Arrays


(Image Source: J. Phys. Chem. B 1997 101 7885-7891)
2D Arrays of Magnetic NCs

                                             Surfactant Stabilized
                                              FePt Nanoparticle
                                              Arrays
                                             Work of Sara
                                              Majetich and co-
                                              workers at CMU
                                             Such Arrays Can
                                              Lead to Further
                                              Miniaturization of
(Image Source: http://www.andrew.cmu.edu/
user/sm70/WebFePtpt1.htm)                     Storage Media
Robust Arrays
 Requirement: “Permanent
  Immobilization” of Nanocrystals in
  Patterned Arrays on Substrates
 Scheme for Making Such Arrays
     Use Self-Organization or Directed
      Assembly to Form Desired Arrays
     Have a Method for Removing the
      Passivating Layer and Permanently
      Immobilizing the NCs on the Substrate
     Heat Treatment of Self-
     Organized Film
                                             This is Clearly the
                                              First Experiment to
                                              Try
                                             But Particle
                                              Coarsening is
                                              Observed to Take
                                              Place in Certain
(Image Source: http://www.andrew.cmu.edu/
                                              Regions
user/sm70/WebFePtpt1.htm)
                                             Clearly not the
                                              Solution
   The Solution
The Majetich Scheme                          The Majetich
                                              Scheme Represents
                                              One Approach
                                             I have an Alternate
                                              Approach that Would
(Image Source: http://www.andrew.cmu.edu/
                                              Not Involve the
user/sm70/WebFePtpt1.htm)                     Sputtering Step
                                             I Plan to Pursue that
                                              Method
Gold Nanowires on Plastics
                                                 Developed by Vivek
                                                  Subramanian’s Group at
                                                  UC-Berkeley
                                                 Sintering of Deposited
                                                  Thiol-Derivatized Au
                                                  Nanocrystals on Plastic
                                                  Substrates
                                                 Sintering Temperature <=
                                                  150o C
(Image Source: Journal of The Electrochemical
Society, 150 ~7! G412-G417 ~2003)
 Sintering of Nanocrystals
                                           Clearly the Study of
                                            Sintering is Important
                                           For Quantitative Models
                                            to be Developed it is
                                            Necessary to
                                            Experimentally Follow the
                                            Process Atomistically
                                           Not Done Yet!
                                           Application of Prudent
(Image Source: Chemical Physics Letters     Methods Should Make
 386 (2004) 390–395)
                                            this Possible
Optical Studies of Thiol-
Derivatized Gold Nanocrystals
                                                Optical Absorption
                                                 Spectra Provide
                                                 Information on the
                                                 Electronic Structure of
                                                 Nanoparticles
                                                There is a Broadening of
                                                 the Surface Plasmon
                                                 Band Centered at 2.4 eV
                                                 Until it is Essentially
                                                 Undistinguishable for
(Image Source: J. Phys. Chem. 1997 101 3706)     Crystallites of Less Than
                                                 2.0 nm in Size
Closer Look I

                                                Onset of Strong
                                                 Absorption near 1.7
                                                 eV
                                                More Distinct for
                                                 Smaller Nanocrystals
                                                This is Attributed to
                                                 the 5d  6sp
                                                 Transition

(Image Source: J. Phys. Chem. 1997 101 3706)
 Closer Look II




(Image Source: J. Phys. Chem. 1997 101 3706)   (Source of Images: J. Phys. Chem. B 1997 101 7885)



  A weak step like structure appears from the onset of the
   spectra of smaller nanoparticles (< 2.0 nm in size)
  The Kubo Criterion Indicates that the Energy Level
   Spacing Near the Fermi Energy is Greater than Thermal
   Energy
  Transition: 5d Band to First Few Unoccupied Levels
Application: Protein Detection

 DNA Targets of Interest can be Amplified by
  PCR thereby Enabling Their Detection and
  Quantification
 Protein Targets cannot be Chemically
  Duplicated
 However, it is Possible to Tag Protein Targets
  with Oligonucleotide Markers
      Then Use DNA Detection to Detect and Quantify
       Target of Interest (Immuno-PCR)
      Issues with Regard to Implementation and
       Detection Sensitivity
Nanoparticle Based Bio-Bar
Code Assay Method
 Mirkin and Co-workers (Northwestern)
  have brought a Nanoflavour to the
  Implementation of Immuno-PCR
 They have applied it to free Prostrate-
  Specific Antigen (PSA) Detection
 How Does the Method Work?
Preparation of Probes
                                              Probe 1: Gold
                                               Nanoparticles Heavily
                                               Functionalized with
                                               Hybridized
                                               Oligonucleotides (the bio-
                                               bar codes) and
                                               Polyclonal Abs to
                                               Recogonize PSA
                                              Magnetic Microparticles
                                               Functionalized with PSA
(Image Source: Science 2003 301 1884-1886)
                                               Monoclonal Abs
Scheme




             (Image Source: Science 2003 301 1884-1886)


 PCR-less Detection of PSA: 30 attomolar
 PCR based Detection of PSA: 3 attomolar
 Orders of Magnitude More Sensitivity that
  Currently Clinically Accepted Assays
Final Observations      Thiol-Derivatized Nanocrystals
                         have been Successfully
                         Synthesized and Studied
                        There are Some Applications
                         with Scope for a Lot More
                        The Area of Robust
                         Compositionally and
                         Morphologically Specific
                         Nanocrystals Has Been Thrown
                         Open
                        While There Has Been Some
                         Success, Number of
                         Outstanding Issues with
                         Respect to Both the Preparation
                         and Characterization Remain
                        This Promises to be an Exciting
                         Area of Research
                        Progress would be Both
                         Scientifically and
                         Technologically Important
Acknowledgements

 Dr. Bruce Tufts


 Professor R. L. Whetten


 Professor Z. L. Wang
Thank You

				
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