1997 MRS Fall Meeting & Exhibit

Chairs

Joseph Akkara, U.S. Army NRDEC
Marie-Isabelle Baraton, Univ of Limoges
Jerry Chen, Eastman Kodak Co
Kenneth Gonsalves, Univ of Connecticut

Symposium Support 

• Baikowski International Corporation
• CERAMEC
• City Technologies Limited
• Corning Incorporated
• Eastman Kodak Company
• Groupe Fournier: Division Tilderm Systems
• Johnson & Johnson Professional
• National Science Foundation
• Oldham S.A. France
• Rhone-Poulenc
• Schlumberger Industries

Proceedings published as Volume 501 
of the Materials Research Society 
Symposium Proceedings Series.

* Invited paper

SESSION FF1: ELECTRONIC NANOMATERIALS 
Chairs: Marie-Isabelle Baraton and Robert J. Nemanich 
Monday Morning, December 1, 1997 
America North (W)

8:30 AM *FF1.1 
SYNTHESIS OF NANOSCALED POWDERS BY LASER EVAPORATION OF MATERIALS. Werner Riehemann, TU-Clausthal, Clausthal-Zellerfeld, GERMANY.

Ultra fine powders with particle diameters less than 100 nm are becoming increasingly important for various electronic, magnetic and chemical applications as well as in nanocrystalline materials as extremely fine grained components. In the meantime there are a lot of methods available to synthesise nanoscaled powders. One of the most versatile and surface controlling production methods is laser evaporation. Interaction of high intensity laser beams with material surfaces leads to the evaporation and subsequent condensation of very small spherical particles with diameters in the order of 10 nm. This means specific surfaces of the powders in the order of 100 m2/g. Depending on the lasers intensity, the surrounding gas, its pressure, and the evaporated material the particles have a diameter ranging from 4 to 20 nm. Their distribution is generally lognormal with a geometrical standard deviation in the narrow range between 1.6 and 1.7. These properties of the powders can be explained by their originating mechanism, nucleation and particle growth in the surrounding gas. With this method different kinds of nanosized powders can be produced like pure metals, alloys, metal oxides, other ceramics and new phases which are stabilized by the small particle size. Using a 1 kW Nd:YAG-laser for alumina nanosized powder production rates of up to 100 g/h can be achieved. Contrary to other synthesis methods e.g. the sol-gel method the produced nanoparticles are in particular free of solvents or other residuals. This makes laser synthesised powders extremely usefull for catalytic or gas sensor applications where defined surface qualities are necessary.

9:00 AM FF1.2 
NANOCRYSTALLINE GALLIUM NITRIDE FROM GALLIUM AZIDE PRECURSORS. Roland A. Fischer, Andre Manz, Alissa C. Frank, Anorganisch-Chemisches Institut, Ruprecht-Karls-Universitat, Heidelberg, GERMANY.

Molecular routs to yield well defined nanocrystals and nanodisperse AlN, GaN and InN are much less developed as compared with oxides (e.g. SiO2, TiO2) or other compound semiconductor materials(e.g. CdSe, GaAs, InP). We demonstrate, that the insoluble and explosive triazido gallium, [Ga(N3)3]x, and a series of less dangerous, low melting and hydrocarbon soluble monomeric Lewis base adducts of the general formula LnGa(N3)3(n=1,3;L=OC4H8. NR3,PR3,O=PR3;R=alkyl group CmH2m+1) serve as molecular precursors for the synthesis of nanocrystalline GaN materials. These precursors were characterized by thermal analysis and were pyrolyzed at 200-400C either in the solid state or in solution (paraffine oil, polyethers and polymanines, fluorocarbons) using surfactants (e.g. log chain amines, phosphines or O=P(n-octyl)3), with or without ammonia or its synthetic equivalents [i.e. HN(SiMe3)2,N(SiMe3)3 or N(SnMe3)3]. The obtaines GaN materials were characterized by XRD, TEM, laser desorption mass spectrometry, FT-IR, RAMAN, dynamic light scattering in solution, BET measurements and PL spectroscopy. For example: 2-3 nm sized GaN nanocrystals were obtained using (Et3N)Ga(N3)3. An extension of this chemistry to AlN and InN and alloys Al1-xGaxN and Ga1-xInxN will be presented.

9:15 AM FF1.3 
REDUCTION OF EXCESS CARBON AND OXYGEN IN Mo2CxOy, Mo2NxOy, W2CxOy, AND W2NxOy NANOPARTICLES PRODUCED BY LASER PYROLYSIS. William W.T. Lee, R. Ochoa*, Keith Wilson, and P.C. Eklund, Center for Applied Energy Research, Univ. of Kentucky, Lexington, KY. *Currently Westvaco Corp. Charleston Research Center, N. Charleston, SC.

Nanoparticles of Mo2CxOy, Mo2NxOy, W2CxOy, W2NxOy were synthesized by CO2 Laser Pyrolysis. In this technique, vapors of metal carbonyls (Mo(CO)6, W(CO)6), mixed with C2H4 or NH3, were reacted by intersecting the precursor gas stream with laser beam. Since C2H4 has a strong absorption band at the CO2 laser's 10.6 m line, C2H4 was often used as the laser power-coupling gas. However, TEM analysis from previous synthesis using C2H4 revealed excess carbon deposits on the particles' surface, and elemental analysis showed excess oxygen. The carbon deposits arose from C2H4 decomposition during the reaction. By avoiding the use of C2H4, carbon levels have been significantly lowered. Heat treatment of the nanoparticles in reducing-gas atmosphere decreased excess oxygen. Carbon Analysis by CHN combustion and oxygen analysis by neutron activation showed an improvement in the stoichiometry, when compared to as synthesized oxycarbides and oxynitrides, yielding nearly pure carbides and nitrides. XRD analysis showed that heat treatment caused little crystallite-size growth.

9:30 AM FF1.4 
MICROSTRUCTURAL EVALUATION OF SINTERED NANOSCALE SiC POWDERS PREPARED BY VARIOUS PROCESSING ROUTES. W.R. Schmidt and G. McCarthy, United Technologies Research Center, E. Hartford, CT; B. Palosz, S. Stel'makh, M. Aloshina and S. Gierlotka, High Pressure Research Center, Polish Academy of Sciences, Warsaw, POLAND; P. Zinn, GFZ (HASYLAB at DESY), Potsdam, GERMANY; D.G. Keil and H.F. Calcote, AeroChem Research Laboratory, Titan Research and Technology, Princeton, NJ.

Microstructural analysis was performed on a variety of crystalline SiC samples previously prepared by three separate processing methods and subsequently sintered under high pressure/high temperature conditions using the cubic anvil cell MAX80 at Hasylab. Microcrystalline SiC was prepared using SHS conditions, while nanocrystalline SiC was prepared using both combustion synthesis methods and polymer precursors. High purity, highly disordered nanocrystalline SiC powders, with average particle diameters below 100 nm, were synthesized via combustion methods from precise mixtures of silane and acetylene, as previously reported [D. G. Keil et al., MRS Symp. Proc. 410, 167-172 (1996)]. The properties of the silicon carbide powders prepared in this manner depended on the initial stoichiometry and pressure of the combustion mixture. Pyrolysis of polymer precursors to SiC was also used to fabricate ceramic powders containing uniformly-sized, highly disordered nanocrystalline SiC grains. The grain sizes ranged from approximately 3 nm to greater than 50 nm, and depended on the initial composition of the polymer, the pyrolysis conditions, as well as the annealling atmosphere, temperature and time. This presentation will describe briefly the preparation methods for each of the SiC powders, experimental details for high temperature and high pressure processing, and analysis results obtained primarily from Transmission Electron Microscopy and Powder X-ray Diffraction experiments.

9:45 AM FF1.5 
SYNTHESIS AND CHARACTERIZATION OF NANOSIZED SILICON CARBIDE. Sylke Klein, Markus Winterer, Horst Hahn, Darmstadt University of Technology, Materials Science Department, Thin Film Division, Darmstadt, GERMANY.

Silicon carbide is an advanced material for demanding structural or functional applications providing excellent high temperature properties with high values for hardness, mechanical strength, thermal conductivity, chemical resistance and high power semiconductivity. Nanocrystalline SiC powders with high specific surface area and purity are required for the production of SiC monolithic and composite ceramics. Nanocrystalline SiC powders are synthesized by the Chemical Vapor Synthesis (CVS) method, a modified Chemical Vapor Deposition (CVD) process. CVS is based on the thermal decomposition of organo-silicon precursors, e.g. tetramethylsilane, in a horizontal tube reactor under low pressure. Powder characteristics such as grain and particle size and distribution, phase and microstructure are studied by a variety of techniques (XRD, BET, IR, HRTEM) as a function of reaction parameters (precursor type and partial pressure, decomposition temperature, residence time). The CVS method provides SiC powders with grain sizes well below 10 nm, low agglomeration, high yield and the potential for particle surface modification and scalability.

10:30 AM *FF1.6 
NANOCRYSTALLINE MATERIALS AS POTENTIAL GAS SENSING ELEMENTS. Gary Coles, University of Wales, Department of Electrical and Electronic Engineering, Swansea, UNITED KINGDOM.

Sensors and Transducers, and in the specific context of this paper gas sensors, are currently amongst the largest growth areas in the modern electronics industry and this seems likely to continue for the foreseeable future. Nanocrystalline materials posses many properties that could make them ideal as potential gas sensing elements with many advantages over their microcrystalline counterparts. Most importantly these include increased surface area coupled with reduced sintering temperatures and times. However, it should also be noted that there are several disadvantages including the comparatively high cost of materials and increased electrical resistance. This paper will review the operating mechanisms of semiconductor type gas sensors and the possible advantages of using nano sized powders to produce gas sensitive devices. Results will then be presented which have been obtained from several materials produced by laser evaporation including alumina, zirconia, barium titanate and tin dioxide in contaminated atmospheres incorporating carbon monoxide, hydrogen and methane.

11:00 AM FF1.7 
TIN DIOXIDE NANO-POWDERS FOR GAS SENSOR APPLICATIONS. R. Vacassy, R. Houriet, C. Plummer1, J. Dutta and H. Hofmann, Powder Technology Laboratory (LTP), Dept. of Materials Science, Swiss Federal Institute of Technology (EPFL), Lausanne, SWITZERLAND; 1Polymer Laboratory (LP), Dept. of Materials Science, Swiss Federal Institute of Technology (EFPL), Lausanne, SWITZERLAND.

SnO2 nanoparticles are of interest for gas sensor applications because the surface area is much larger compared to conventional powders. Thus, interactions between the material and the gases, which occur on the surface sites of the particles, are increased considerably. The preparation of SnO2 powders has been investigated following two methods: the forced precipitation in an emulsion media and the precipitation from a homogeneous solution. Spherical nanoparticles in the 10 to 71 nm range and with a narrow size distribution were synthesized by both precipitation routes. In both cases, it has been demonstrated that the most important parameter which controlled the particle size was the nature of the associated anion. This associated anion or ligand has to form a strong complex with the precipitation cation in order to limit the concentration of free cation in the solution. This greatly influences the agglomeration/growth kinetics during the precipitation. The effect of two chelating ligands (acetate and acetylacetonate) which resulted in the Sn)2 nanopowders formed of 2-10 nm crystallites will be presented and discussed. Preliminary results on the gas adsorption studies on pellets formed from these powders will be presented.

11:15 AM FF1.8 
SYNTHESIS AND CHARACTERIZATION OF ANTIMONY-DOPED TIN OXIDE NANOPHASE MATERIALS FOR ELECTROCHROMIC APPLICATIONS. J. Liu, Monsanto Corporate Research, Monsanto Co, St. Louis, MO; J.P. Coleman, P. Madhukar, Growth Enterprise Division, Monsanto Co, St. Louis, MO.

Antimony-doped tin oxide (ATO) materials have many interesting and useful properties for industrial applications. Important uses of ATO include anti-static pigments, catalysts, electrochromic devices, gas sensors, etc. Although the electro-optical and the structural properties of ATO materials with low antimony dopant levels have been extensively investigated, the fundamental structural/optical properties of heavily doped ATO materials have not been well understood. Recently, we synthesized ATO nanophase materials containing up to 43 at.% antimony with enhanced electrochromic properties. It has been found that antimony inhibits the growth of tin oxide nanoparticles during annealing. The average crystal size of the ATO particles depends on the dopant level, the annealing conditions as well as the synthesis processes. We describe here the results of a systematic study of the structural evolution of antimony-doped tin oxide nanoparticles. The relationship between the nanostructure of the synthesized ATO materials and the enhanced performance of the corresponding electrochromic devices will be discussed.

11:30 AM FF1.9 
ON THE STOICHIOMETRY, SURFACE COMPOSITION AND STRUCTURAL CHANGES OF SnO2 NANOPARTICLES WITH CALCINATION TREATMENTS FOR GAS SENSOR APPLICATIONS. Angel Dieguez, Albert Romano-Rodriguez, Josep-Lluis Alay, Juan Ramon Morante, EME, Department of Applied Physics and Electronics, University of Barcelona, Barcelona, SPAIN; Nicolae Barsan, Udo Weimar, Wolfgang Göpel, Institute of Physical and Theoretical Chemistry, University of Tübingen, Tübingen, GERMANY.

Hydrated tin dioxide nanocrystalline powders, obtained by the sol-gel method and with a crystallite size of 3 nm, have been calcinated at temperatures up to 1000C and times up to 24 hours. Several structural characterization techniques such as TEM, XRD, XPS, FTIR, and Raman scattering have been used to analyze the surface, stoichiometry, grain size, and morphology of the nanoparticles. Under this analysis, two different temperature regimes are indentified. The first one, up to about 400C, corresponds to a slow increase in the nanoparticles size up to 10nm, which was characterized by HREM and Low Frequency Raman. A strong substoichiometric oxide and a rapid reduction of the water content were also found. Moreover, the Raman spectra of these nanoparticles show, together with the Raman peaks associated to the SnO2 cassiterite, the presence of a band at lower wavenumbers than the characteristic A1g mode that decreases in intensity and shifts to lower wavenumbers with increasing calcination temperature at the same time that the A1g mode moves to its reported position around 636 cm-1 and increases its intensity. The second regime, above 500C, corresponds to region in which a stoichiometric oxide is formed. The fast increase of the crystallite size (up to 100nm) and improvement of the crystallinity, together with a deagglomeration and faceting of the nanoparticles and a lower content of water, are also characteristic of this regime. The region between 400 and 500C corresponds to a quite sharp transition for stoichiometry. Attempt will be made to model the evolution of the nanoparticles with the calcination temperature, emphasizing the relationship between the state of surface of the nanoparticles and the increase of the rate of grain growth and stoichiometry.

11:45 AM FF1.10 
DISPERSION OF METAL OXIDE NANOPARTICLES IN CONJUGATED POLYMERS: INVESTIGATION OF THE TiO2/PPV NANOCOMPOSITE. Marie-Isabelle Baraton, LMCTS, ESA CNRS, Faculty of Sciences, Limoges, FRANCE; Lhadi Merhari, CERAMEC, Limoges, FRANCE: Kenneth E. Gonsalves, Polymer Programme at the Institute of Materials Science & Department of Chemistry, University of Connecticut, Storrs, CT.

Smart design of conjugated polymers and tailoring of their optical and electronic properties are essential for the development of advanced optoelectronic devices. Poly(p-phenylene vinylene) (PPV) has been successfully used in the fabrication of promising light emitting diodes. Whereas its is polymer matrix can enhance its non linear optical properties, very little is known about the effect of semiconducting metal oxide nanoparticles on both electrical and optical properties of conjugated polymers. As a preliminary step, we have studied the grafting of PPV and related molecules on nanosized TiO2 particles by vibrational spectrometries. This assessment of the surface interactions is critical for controlling the nanoparticles deagglomeration process. Then, using a non contact measurement technique based on infrared spectroscopy we have investigated the electrical conductivity of the TiO2/PPV nanocomposite versus adsorption of various gases.

SESSION FF2: ELECTRONIC AND OPTICAL NANOMATERIALS 
Chairs: Kenneth E. Gonsalves and 
Miguel Jose-Yacaman 
Monday Afternoon, December 1, 1997 
America North (W)

1:45 PM *FF2.2 
FORMATION AND CHARACTERIZATION OF NANOSCALE EPITAXIAL ISLANDS ON Si. R.J. Nemanich, Woochul Yang, Y.L. Chen, H. Ade, Department of Physics, and Department of Materials Science, North Carolina State University, Raleigh, NC.

Nanoscale epitaxial metallic islands are formed on Si through the deposition of thin layers (<1nm) of selected metals (Ti, Co, Pt) on clean Si (100) and (111) surfaces. The structure and morphology of the epitaxial islands was studied by TEM and AFM. Moreover, the dynamics of the formation process was studied in situ with photo-electron emission microscopy (PEEM). The results show several unusual effects. For Ti or Co films deposited on Si(100), similarly sized islands uniformly distributed over the surface are observed. Annealing to 1100C results in oriented and faceted structures. Deposition of Si onto the oriented TiSi2 islands results in a transition to nearly spherical epitaxial islands that are largely imbedded in the Si. Low temperature Si deposition results in imbedded islands of 20nm. The results indicate that diffusion processes dominate the low energy faceted surfaces in determining the shapes of the islands. The PEEM results for Pt on Si indicate first the formation of similarly sized islands uniformly distributed over the surface. As the temperature is increased, some of the islands are observed to move and collect other islands much like a snowball rolling down a hill. The islands eventually stop. The processes are described in terms of the surface and interface energies, the island size and the substrate strain.

2:15 PM FF2.3 
SURFACE ALLOY FORMATION OF Mn ON Cu(100) AND Cu(110): KINETICS, ENERGETICS AND ATOMIC MECHANISMS. M. Wuttig, C. Ross, T. Flores, Institut für Grenzflachenforschung und Vakuumphysik, Forschungszentrum Julich, GERMANY.

Alloy formation at the surface of a bulk material offers the potential of tailoring surface controled properties. We have used low energy electron diffraction (LEED) and scanning tunneling microscopy (STM) to study the kinetics, energetics and atomic mechanisms responsible for surface alloy formation of Mn on Cu(100) and Cu(110). By exploiting the pronounced corrugation, incorporated Mn atoms were distinguished from Cu atoms in the STM images on Cu(100). The mobility of these incorporated atoms depends critically upon coverage. For small Mn coverages, a diffusion coefficent of is determined. A drastically enhanced Mn mobility is observed for Mn coverages around 0.3 monolayers Mn. This fast mobility is correlated with rapid changes of the surface morphology. The incorporation of Mn occurs preferentially in the vicinity of island edges and substrate steps. In particular, a correlation with the kink density of steps and the rate of incorporation at the lower terrace is observed. This indicates that the interlayer mass transport necessary for Mn incorporation into the lower terrace is particularly efficient close to kinks. Atomic exchange processes and vacancy mechanisms which proceed in the vicinity of kinks can explain this observation. Vacancy annihilation by Mn adatoms is the only process which at least qualitatively can account for both the observed coverage dependence of Mn incorporation and the importance of kinks.

2:30 PM FF2.4 
A METASTABLE-ATOM DEEXCITATION SPECTROSCOPY (MDS) STUDY ON THE FIRST ATOMIC LAYER OF A POLYCRYSTALLINE TITANIUM SURFACE. Mitsunori Kurahashi, Yasushi Yamauchi, National Research Institute for Metals, Tsukuba, Ibaraki, JAPAN.

Properties of the first atomic layers of surfaces are closely related to those of nano-sized particles. Most surface analysis techniques, however, give us information averaged over at least a few atomic layers below the surface rather than on the first atomic layer. A distinct surface sensitivity can be achieved by electron emission induced by impact of thermal metastable atoms, a method called by the metastable-atom deexcitation spectroscopy (MDS). In spite of its extremely high surface sensitivity, the MDS has been applied to only rather limited surface systems. In the present study, we have developed a new type of metastable atom beam source, which can be operated at the pulsed-discharge mode producing more than 11014 He metastable atoms/sec/sr. Using this source, we have obtained the MDS and UPS spectra of a polycrystalline titanium surface. This is the first report of the MDS spectra of a titanium surface. Based on the measured spectra, we have discussed the electronic structure of the first atomic layer of a polycrystalline titanium surface.

3:15 PM *FF2.5 
POLYMER-PARTICLE NANOCOMPOSITES SYNTHESIZED IN INVERSE MICELLES AND ORGANOGELS. Vijay John, Gary McPherson, Sukanta Banerjee, SiChu Li, Tulane University, Department of Chemical Engineering, New Orleans, LA; Charles O'Connor, Advanced Materials Research Institute, University of New Orleans, New Orleans, LA; Joseph Akkara, U.S. Army Natick Research, Development and Engineering Center, Natick, MA.

Synthesis of magnetic and semiconductor particles in self-assembling media containing organic ligands, results in materials with novel surface controlled properties. We describe research into the synthesis of such particles in microstructured media such as inverse micelles and specific lyotropic liquid crystal phases. A novel aspect is the coupled synthesis of conjugated polymers in these systems, which leads to the preparation of polymer-particle nanocomposites with optical and/or magnetic properties. These nanocomposites can be prepared in the morphology of microspheres with controlled internal porosities. The nanocomposites are also used to prepare magnetic coatings and in thin film applications. A second aspect of the research is the encapsulation of magnetic and semiconductor particles in optically clear organogels. A specific gel studied is the system of immobilized inverse micelles where small amounts of dihydroxynaphthalenes are used to bridge micelles and create entangled chains leading to the gelation of a micellar solution. These gels are doped with magnetic and semiconductor nanoparticles. The gel environment stabilizes surface characteristics of these materials and their photoluminescence and magetic properties are contrasted with properties in solution.

3:45 PM FF2.6 
CHEMISTRY OF SILICON NANOCRYSTALLITE SURFACES IN POROUS SILICON. Michael J. Sailor, Theresa F. Harper, Jae Hee Song, Christie Canaria, Aetna Wun, Department of Chemistry and Biochemistry, University of California at San Diego, La Jolla CA; Jillian M. Buriak, M. Reza Ghadiri, The Scripps Research Institute, La Jolla, CA.

Luminescent porous silicon has attracted attention for potential use in electroluminescent, photovoltaic, and chemical or biological sensor devices. In order to take advantage of the photoluminescent properties of the quantum-confined nanocrystallites in this material, mild chemical reactions that functionalize the silicon surface must be developed. These studies also allow an investigation of the relationship between the surface and the emissive properties of the quantum nanocrystallites within the porous silicon matrix. Reactions that involve chemical and electrochemical oxidation of silicon-silicon bonds (with halogens or carboxyllic acids), abstraction of surface hydride species (with quinone-based molecules), and formation of silicon-carbon bonds (with alkyllithium or metal-catalysed hydrosilylating reagents) will be presented. The chemical reactions allow the introduction of chemical specificity to chemical and biological sensors based on photoluminescence quenching or related optical phenomena.

4:00 PM FF2.7 
OPTICAL PROPERTIES OF NANOPARTICLES-CONTAINED PLASMA POLYMER FILMS. Andreas Heilmann, Michael Quinten, Andreas Kiesow, Technical University Chemnitz-Zwickau, Institute of Physics, Chemnitz, GERMANY.

The microstructure of thin metal-insulator composite films is determined by the size and shape of the metal (gold, silver) nanoparticles and is influenced by the metal-insulator interface. Moreover, the interface between film and substrate and the film surface have to be considered. The optical properties of such metal-insulator thin films are determined by the plasma resonance absorption of the metal nanoparticles. Spectral position, halfwidth and intensity of the optical plasma resonance absorption strongly depend on the particle size and shape, and on the dielectric properties of the of the particle material and the surrounding medium. For plasmapolymer metal composite films the particle size and shape distributions were obtained by transmission electron microscopy (TEM) in lateral and vertical (XTEM) direction. With image processing, size and shape distribution histograms were made. This detailed knowledge of the microstructure was taken into account when calculating the optical properties using Rayleigh-Gans theory. The optical extinction was calculated using the size and shape of a single particle and summarizing for a particle assembly. The calculations are in very good agreement with the optical spectra measured using common spectroscopy.

4:15 PM FF2.8 
OPTICAL PROPERTIES OF GOLD CONTAINING POLY(ACRYLIC ACID) COMPOSITES. S.M. Scholz, J.-C. Valmalette, G. Carrot, J. Hilborn, J. Dutta, and H. Hofmann, Powder Technology Laboratory and Polymer Laboratory, Department of Materials Science, Swiss Federal Institute of Technology (EPFL), Lausanne, SWITZERLAND.

There is strong interest in the research & development of the particle/polymer composite technology for functional applications. Current activities are directed towards polymer assisted synthesis of ultrafine metal or semiconductor particles in solution, with an ultimate goal to arrange the particles in a matrix in well-controlled fashion, for possible electro-optical applications. In the present work the optical properties of poly(acrylic acid) polymers containing gold chloride have been investigated. This material system permits synthesis of gold nanoparticles by the reduction of gold chloride. The polyelectrolyte initially forming upon mixture of the reagents shows a gelating behavior. In-situ reduction into gold clusters can be achieved by several ways. Optical absorption/extinction spectra as well as photoluminescence and photoluminescence excitation spectra will be presented and discussed. The oxidation state of gold atoms will be discussed as interpreted from measurements of optical and X-ray photoelectron spectroscopy. Different possible combinations of gold ligands and co-ordinations states will be considered in the discussion. Gold may be bound in the form of complexes, polyelectrolytes, or in form of nanoparticles or larger aggregates depending on the relative concentrations of the reagents and polymer molecular weight. Preliminary results on the electrical resistivity of these composites will also be presented and discussed.

4:30 PM FF2.9 
EUROPIUM DOPED B++-Al2O3 NANOPARTICLE FORMATION. Tom Hinklin, Rita Baranwal, David Treadwell and Richard M. Laine, Department of Materials Science and Engineering, University of Michigan, Ann Arbor, MI.

A simple and inexpensive one-step route to B++-Al2O3 ceramic precursors has been developed. In the process, Al(OH)3, and NaOH are reacted with triethanolamine in ethylene glycol solvent at 200C. The resulting complex is soluble in ethanol and can be flame spray pyrolysed (FSP) to form nanoparticles of the B++-Al2O3 composition. B++-Al2O3 has been shown to be an excellent host matrix for europium phosphoresence. The discussion will focus on the utility of the FSP method to provide exact control of dopant concentrations, the formation of B++-Al2O3 and the potential to optimize luminescence behavior.

SESSION FF3: MAGNETIC NANOMATERIALS AND IMAGING 
Chairs: G. L. Hagnauer and J. T. Vijay 
Tuesday Morning, December 2, 1997 
America North (W)

8:30 AM *FF3.1 
SURFACE-GENERATED ANOMALOUS BEHAVIOR IN MAGNETIC OXIDE NANOSTRUCTURES. Ami E. Berkowitz, Richard H. Kodama, Kentaro Takano, Univ of California-San Diego, Physics Dept and Center for Magnetic Recording Research, La Jolla, CA; Frederick T. Parker, Frederick E. Spada, Univ of California-San Diego, Center for Magnetic Recording Research, La Jolla, CA; Simon Foner, Edward J. McNiff, Jr., MIT, Francis Bitter Magnet Laboratory, Boston, MA.

Magnetic oxide nanoparticles exhibit a number of remarkable magnetic properties which are induced by their unique surface spin states. These surface states may arise from low coordination, broken exchange bonds, roughness, or various surface treatments. An important factor in determining the nature of these surface spin states is that in both ferrimagnetic and antiferromagnetic oxides, the localized magnetic exchange interactions between adjacent 3d cations involve the p-orbitals of the intervening oxygen anions, i.e., superexchange. We shall discuss three examples of surface-generated behavior in magnetic oxide nanoparticles which are of particular significance in magnetic information storage: 1) Surface-treatment of Fe-oxide ferrimagnetic fine particles with Co and Na-polyphosphate for enhanced coercive force; 2) Disordered surface spin states in Ni-ferrite nanoparticles which produce a wide range of anomalous static and dynamic properties; 3) Uncompensated spins on antiferromagnetic oxide films which are responsible for the ability of these films to bias ferromagnetic films to which they are coupled. Numerical atomic modeling of the spin configurations in example 2) and of the interface topography in 3) have shown how they produce the observed behavior. The current status of the analysis of example 1) will also be presented.

9:00 AM FF3.2 
DISPERSION OF SAMARIUM COBALT NANOPARTICLES IN A POLYMER MATRIX. Y. Jin, K. Chowdary and S.A. Majetich, Department of Physics, Carnegie Mellon University, Pittsburgh, PA.

Samarium cobalt alloys are important permanent magnet materials due to their high energy products and corrosion resistance. Bonded magnets, or powders of permanent magnets dispersed in a polymer matrix, are the fastest growing product of the permanent magnet industry. Here we focus on two important issues; the optimal size of the permanent magnet particles, and the prevention of clumping, which has been shown to reduce the coercivity.1 Single phase nanoparticles of samarium cobalt were prepared by ball milling 10 m SmCo5 powder in argon. To vary the average size, samples were extracted after different milling times. In some cases, the particles were dispersed in a polymer matrix by co-milling with fine thermoplastic powders. In other cases the resulting powders were dispersed by mixing with epoxy. With the co-milling, there was a high probability that the SmCo5 particles would become embedded upon collision with the thermoplastic, thereby minimizing agglomeration with other SmCo5 particles. The resulting powders were thermally compacted to form nanocomposites. Microtome sectioning techniques were used to prepare samples for transmission electron microscopy, to determine the average size, shape, size distribution and degree of dispersion. Hysteresis loops for the samples were measured with a SQUID magnetometer. The samples in an epoxy matrix, where clumping is present, were shown to have coercivities, Hc, which decreased for average size D > 25 nm according to a powder law: Hc D-1/3. Reducing the degree of interactions between particles is shown to significantly increase the coercivity2 The size dependence of the coercivity in the samples dispersed in the thermoplastic reveals the isolate single particle coercivity which is compared with the predictions of Stoner-Wohlfarth theory. Comparision of remanent magnetization measurements on clumped and dispersed samples as a function of particle size will quantify the relative contributions of magnetostatic and exchange interactions in reducing the coercivity in the clumped samples.

9:15 AM FF3.3 
WETTABILITY CONTROLLED BY MAGNETIC FIELDS. Virginie Ponsinet, Michel Maman, Laboratoire de Physique de la Matière Condensée, Collége de France, Paris, FRANCE.

We are studying the modifications induced by the action of an external magnetic field on the surface structure and on the wettability of composite materials, obtained from combination of a polymer matrix and magnetic solid particles. Two types of composites are considered. On one hand, micron-size spherical ferromagnetic particles are anchored at the surface of a polymer film: the surface is modified by the action of magnetic field gradients while the film is heated above its glass transition. The dominant effect is shown to be the lateral displacement of the particles and is described in two distinct regimes according to the strength of the field gradients. On the other hand, ferromagnetic nanoparticles with a strongly preferred magnetisation axis are incorporated inside a rubber film. Following a calculation of Raphael and DeGennes, the conditions in which a tangential magnetic field can deform the surface of the film are discussed.

9:30 AM FF3.4 
SYNTHESIS OF NEARLY MONODISPERSE COBALT NANOCRYSTALS AND THEIR ASSEMBLY INTO MAGNETIC SUPERLATTICES. Shouheng Sun and C. B. Murray, IBM T. J. Watson Research Center, Yorktown Heights, NY.

High temperature reduction of cobalt salts in the presence of long-chain carboxylic acids and trialkylphosphines produces stable cobalt colloids. Cobalt nanocrystal samples with less than 5% (st. dev.) in diameter are isolated by size selective precipitation. Nanocrystal size is tuned from 30-120 angstroms by adjusting the ratio of stabilizing ligands. Deposition of these uniform cobalt particles on a variety of substrates results in the assembly of 2-D and 3-D magnetic superlattices. A combination of X-ray scattering techniques and transmission electron microscopy is used to characterize the dispersed nanocrystals and assembled superlattices. Size dependant magnetic phenomena are studied with the use of SQUID magnotometry.

9:45 AM FF3.5 
MAGNETIC PROPERTIES OF GIANT MAGNETORESISTIVE SPIN VALVES WITH MODIFIED INTERFACES USING SURFACTANT Pb. Harsh Deep Chopra, Thayer School of Engineering, Dartmouth College, Hanover, NH; L.J. Swartzendruber, P.J. Chen, and W.F. Egelhoff, Jr., NIST, Gaithersburg, MD.

The phenomenon of giant magnetoresistance in magnetic multilayers has recently attracted great attention, due both to the new physics in explaining their spin-dependent electron transport properties, and their technological importance in field-sensing applications, such as read-heads in high density data-storage devices. The nanostructure and magnetic properties of symmetric spin-valves of the type NiO(50nm)/Co(2.5nm)/Cu(2.2nm)/Co(3.5)nm/Cu(2.2nm)/Co(2.5nm)/ NiO(10nm) will be discussed. In order to modify the different growth behavior of Co and Ca layers (arising from the difference in surface energy of these two metal species), surfactant Pb in monolayer thicknesses was deposited at selected interfaces. X-ray photoelectron spectroscopy during growth, showed that Pb floats out during successive deposition of metal layers, and high resolution TEM show altered Co/Cu interfaces. Such tailored growth of few monolayers of successive Co and Cu layers succeeds in reducing deleterious interlayer magnetic coupling by more than an order of magnitude. The magnetic behavior of such multilayers will be explained in terms of SQUID measurements and domain structure. Results show that magnetization reversal in the middle Co layer occurs due to nucleation and local annihilation of fine domains (1-5 microns). The observed domain structure will be explained in terms of the film morphology, interfacial characteristics and interlayer magnetic interactions.

10:30 AM *FF3.6 
CHARACTERIZATION OF NANOSCALED METALS USING HIGH RESOLUTION TEM AND COMPUTER SIMULATIONS. M. José-Yacamán*, J.A. Ascencio, M.E. Espinosa-Pesqueira, C. Gutiérrez-Wing and M. Marín-Almazo, Instituto Nacional de Investigaciones Nucleares, México, MÉXICO; *Also at: Instituto de Física, Universidad Nacional Autónoma de México, México, MÉXICO.

The characterization of Nanoscaled Materials is very important in order to produce useful materials and therefore obtain high value added materials. In order to characterize the structure we need to use local techniques such as High Resolution TEM. However, the particles composing a nanostructured material can be oriented in a large number of angles with respect to a low index direction. It is necessary therefore to calculate the structure in many angles and compare the experimental image with the theoretical one. We have performed a systematic study of the images of metal particles for eight structures: regular decahedron, Ino's decahedron, Mark's decahedron, icosahedron, octahedron, truncated octahedron, cubo-octahedron and amorphous clusters. We found as a result of a systematic study that the preferred shapes for gold particles covered with a thiolate and with a size <20 are truncated octahedron in the FCC particles and the Mark's decahedron in the decahedral particles. We also show the possibility of other shapes being also present. We show that our methods can be applied to a wide variety of materials including quantum dots embedded in a matrix.

11:00 AM FF3.7 
NUCLEAR MAGNETIC RESOANCE (NMR) AS A TOOL FOR SURFACE AND INTERFACE CHARACTERIZATION OF NANOSCALED MATERIALS. Pierre-Andre Vuissoz, Valerio Scarani, Vincent Bonny, Jean-Philippe Ansermet, Institut de Physique Experimentale, Ecole Polytechnique Federale de Lausanne, Lausanne, SWITZERLAND.

The use of nuclear magnetic resonance (NMR) as a tool to characterize phenomena at surfaces of nanosized grains and the structure of interfaces of nanostructured materials will be presented. After giving the basic principles and feasibility criteria of surface NMR, its analytical power will be illustrated by means of selectect examples from the authors work and the work of others. Chemisorption (grafting) on ultrafine grains in vacuum as well as in an electrolyte or a matrix can be studied, including the determination of molecular structures of the adsorbate, bonding site and surface mobility. The physical properties of the the surface of some nanosized metals (Cu, Pt, Rh, Ag) can also be investigated. In the case of magnetic nanostructures, NMR can be used to determine the crystalline structure and the roughness of interfaces.

11:15 AM FF3.8 
SERS ACTIVE NANOPARTICLES IN PLASMA TREATED SILVER SURFACES. G. Compagnini, B. Pelligra and B. Pignataro, Dipartimento di Scienze Chimiche, Catania, ITALY.

A plasma oxidation-reduction process has been found to be suitable to produce silver surfaces showing surface enhanced Raman (SERS) activity. SERS spectra of monodisperse polystyrene films and of other smaller molecules like methylpyrrolidone, adsorbed on active silver surfaces, have been obtained in order to study true correlation between enhancement and nanomorphology as probed by Atomic Force Microscopy. It was found that the enhancement is strongly correlated with a coalescence of the initially present silver grains (10-50 nm in size). This coalescence leads to the formation of 100-300 nm silver hills in which each silver grain is still clearly distinguishable. The increase of the effective surface area due to the particle coalescence has been correlated to the SERS enhancement in straightforward fashion. The effect of surface morphology on the vibrational features of the investigated compounds will be also discussed in terms of molecular orientation of the adsorbate with a comparison to the known Raman bulk selection rules.

11:30 AM FF3.9 
FORMATION OF Au55 NANOCAPILLARIES BY ATOMIC FORCE MICROSCOPY. R. Houbertz, Th. Feigenspan, R. Steinkampf, and U. Hartmann, Institute of Experimental Physics, University of Saarbrücken, Saarbrücken, GERMANY.

By using atomic force microscopy (AFM), nanocapillaries from ligand-stabilized Au55 clusters adsorbed on highly oriented pyrolitic graphite (HOPG) were generated. The Au55 clusters were deposited onto the substrates from a solution containing Au55 clusters. After evaporation of the solvent, the samples were investigated immediately by AFM under ambient conditions. The resulting surface morphologies, which can be adjusted by varying the concentration of the cluster solution, were investigated in a dynamic mode. Furthermore, quasistatic force-distance curves [F(z)] were taken on selected locations of the surfaces, leading to small Au55 nanocapillaries. The F(z) curves were taken for varying velocities at fixed force as well as for varying forces at fixed velocity, leading to characteristic dependences on the production process. The nanocapillaries generated by the tip-sample contact were then imaged again in a dynamic mode. Additionally, the relaxation of the capillaries was investigated. The results will be discussed with respect to the JKR model. The data are supported by current-distance and current-time curves.

11:45 AM FF3.10 
STUDY OF THE LOCAL ATOMIC ORDER IN Si/C/N NANOPOWDERS BY X-RAY PHOTOELECTRON SPECTROSCOPY. A. Gheorghiu, G. Dufour, P.A. Bonnefont, C. Sénémaud, Laboratoire de Chimie-Physique, URA CNRS, Paris, FRANCE; M. Cauchetier, CEA, Saclay, Gif-sur-Yvette, FRANCE.

Nanosized Si-based powders have revealed in the recent years a wide interest due to their possible applications in the range of ceramics with thermomechanical properties. We present in this paper a study of local atomic environnement in Si/C/N nanopowders by X-ray photoelectron spectroscopy (XPS). The samples have been prepared by the interaction of a CO2 laser beam with an aerosol of a liquid precursor hexamethyldisilazane. Powders with atomic concentration ratio C/N in the range 0.34 to 1.34 have been synthetized by adjusting the experimental conditions. By XPS we have investigated the Si 2p, C 1s and N 1s core levels which give informations on the local atomic environnement of each atomic species in the nanopowders. We have focused our attention on samples with intermediate compositions close to C/N equal 0.6 which have interesting properties concerning annealing treatments. As-formed powders are amorphous and exhibit a local chemical disorder, with the existence of mixed Si CxN4-x tetrahedra around Si atoms. The evolution of the local order with annealing treatments under argon up to 1600C depends strongly on the C/N value. For C/N close to 0.6, crystallisation is observed at higher temperature as compared to samples with higher or lower C/N values. From the study of both C 1s and N 1s core levcls, the presence of C-N bonds around both C and N atoms after 1500C annealing is evidenced; C-C bonds are also detected. C-N bonds are still observed after a 1600C annealing and in this case both carbide and nitride phases are present. The results are discussed in relation with other experimental data obtained independently for the same samples.

SESSION FF4: NANOCOMPOSITES AND COATING 
Chairs: Ami E. Berkowitz and Chad A. Mirkin 
Tuesday Afternoon, December 2, 1997 
America North (W)

1:30 PM *FF4.1 
CHEMICAL SYNTHESIS AND PROPERTIES OF NANOSTRUCTURED POWDERS AND COATINGS. G.M. Chow, Materials Science and Technology Division, Naval Research Laboratory, Washington, DC.

An overview of our research activities in fabrication of nanostructured powders and coatings is presented. Examples include the synthesis of metal powders and coatings by aqueous and nonaqueous Polyol methods, and oxide powders and coatings by sol-gel and colloidal methods; the nitridation of oxide powders; and the synthesis of dispersed metal powders by surfactant-mediated methods The relationships between the synthetic conditions and the phases, microstructures, control of particle size and agglomeration, impurities incorporation and defects formation will be addressed. The following will be specifically discussed: the effects of impurities on metallic metastable alloy formation and the subsequent thermally induced segregation the factors controlling the impurities incorporation in the surface and buried interfaces, and the adhesion of metal coatings in the Polyol process, the effects of surface oxynitride and agglomeration of nitride particles on pressureless sistering; and the factors affecting the formation of crystal defects such as multiple twins of metal particles at room temperature reactions.

2:00 PM FF4.2 
A NEW APPROACH TO THE FABRICATION OF "SMART" NEAR-SURFACE NANOSTRUCTURED COMPOSITES. Laurence Gea, L.A. Boatner, S. Honda, T.E. Haynes, B.C. Sales, and F.A. Modine, Solid State Division, Oak Ridge National Laboratory, Oak Ridge, TN.

A new method for the formation of ``smart'' near-surface nanoscale composites has been developed. In this approach, small precipitates of active phases are embedded in the near-surface region of the material that is to be modified by a combination of ion implantation and thermal processing. The dispersion concentration, and microstructure, of the nanocrystals in the substrate material can be tailored through a careful choice of processing parameters - making this approach well suited to high-value-added, high-tecnology applications. The applicability of this approach to forming ``smart'' surfaces on otherwise inactive materials is illustrated by the cases of VO2 precipitates embedded in Al2O3 single crystals [1] to create a medium suitable for optical applications - including optical data storage. Most recently this concept has been extended to the fabrication of magnetic-field-sensitive nanostructured surfaces by forming magnetostrictive precipitates of materials such as Ni, RFe2 (with R = Tm, Tb, Sm) that are embedded in various single crystal-oxide hosts. These nanostructured, active surface composites have been characterized using XRD, RBS, TEM, and magneto-optical techniques.

2:15 PM FF4.3 
PREPARATION AND CHARACTERIZATION OF CONCENTRIC-TUBULAR COMPOSITE MICRO- AND NANOSTRUCTURES USING THE TEMPLATE SYNTHESIS METHOD. Charles R. Martin, Veronica M. Cepak, Colorado State University, Dept. of Chemistry, Fort Collins, CO.

The template method is a general route for the preparation of tubular micro- and nanostructures. The template method entails synthesizing a desired material within the pores of a microporous membrane. The membranes employed have cylindrical pores with monodispersed diameters. A tubule or fibril of the desired material is synthesized within each pore. In this presentation we will discuss using the template method to prepare concentric tubular composite micro- and nanostructures. These composite micro- and nanostructures consist of an outer tubule composed of one material encapsulating concentric inner tubules composed of other materials. Tubular composites of this type consisting of metals, carbons, semiconductors, polymers, and Li-ion intercalation materials have been prepared. The chemical strategies used to prepare these composite structures include electropolymerization of electronically conductive and insulating polymers; electrodeposition of metals and semiconductors; graphitization of polymer precursors; chemical vapor deposition synthesis; and sol-gel synthesis. The fabrication and characterizatioon of select composite micro- and nanostructures will be presented and discussed.

2:30 PM FF4.4 
NICALON REINFORCED STRONTIUM ALUMINOSILICATE CERAMIC MATRIX COMPOSITES VIA INFILTRATION OF A SAS PRECURSOR / NANOPARTICLE SUSPENSION. Tom Hinklin, Siew S. Neo, Rita Baranwal and Richard M. Laine, Department of Materials Science and Engineering, University of Michigan, Ann Arbor, MI.

A simple and inexpensive one-step route to preceramic polymers has been developed [Oxide One Pot Synthesis (OOPS) Process]. In the OOPS process, SiO2, Al(OH)3, and MO (M = Mg, Sr, Ba) are reacted with triethanolamine in ethylene glycol solvent at 200#161#C. In addition to being an alternative to traditional melt processing of ceramics and glasses, these precursors have also been used to form nanoparticles using a flame spray pyrolysis technique. This discussion will focus on the development of SrAl2Si2O8 (SAS) ceramic matrices in Nicalon reinforced composites via an infiltration process using a suspension of SAS nanoparticles (20-150 nm) in a SAS precursor / methanol solution. The phase transformations and microstructures formed after pyrolysis at selected temperatures and times are examined using TGA, DTA, XRD, SEM, TEM and DRIFTS.

2:45 PM *FF4.5 
SURFACE PROPERTIES OF BORIDE/NITRIDE NANOSCALE FILMS. Rostislav Andrievski, Institute for New Chemical Problems, Russian Academy of Sciences, Chernogolovka, Moscow Region, RUSSIA.

Nanocomposite boride/nitride materials im general and films in particular are attracting the most notice because of their promising physical-mechanical properties. In the case of films the latters are closely connected with sur- face-controlled conditions. Titanium nitride/titanium nitride films, produced by r.f.magnetron sputtering different targets, have been examined by TEM, SAED, SEM, XRD, XPS, AES, and AFM. They were characterized by very small crystalli- tes size (below than 10 nm). Only cubic and hexagonal phases, such as sodium chloride and aluminium diboride types, have been revealed by XRD and SAED. The formation of substoichiometric and superstoichiometric compounds, such as com- plex borides and nitrides accordingly, has been fixed by AES and XPS. The dif- ferent surface topography of cubic and hexagonal films has been noted. All the- se features are carefully discussed with data of fractured cross-sections, ob- tained by high resolution SEM images, as well as with information of hardness and electrical properties of films. Two types of nanostructured films fracture under Vickers indentor connected with gomogeneous and ungomogeneous deformation are described in detail.

3:45 PM *FF4.6 
NANOCOMPOSITE PARTICLES FOR THE PREPARATION OF ADVANCED NANOMATERIALS. P. Somasundaran and T. Chen, Columbia Univ, Dept of Chemical Engineering, Materials Science, and Mining Engineering, New York, NY.

New composites based on nano-size particles provide a promising route to the fabrication of novel materials for advanced technology applications. To produce desired materials, it is important to control the composition and distribution of nanoclusters within the bulk or surface coating of nanostructured materials. Towards this purpose, we have developed a novel method of processing nanocomposite particles utilizing colloidal chemistry techniques to tailor their microstructure. Unique composite aggregates of nanoparticles with a core-shell structure were prepared using a special scheme of controlled polymer adsorption. Polymers which specifically adsorb on both nano- and micron- size particles are used as tethers to enable coating and to enhance the cluster integrity. Nanocomposite particles consisting of micron-size alumina or silicon nitride as cores and nano-size alumina, titania, or iron oxide as shell particles have been successfully prepared using this process. The surface charge of the core particles was found to be reversed after the adsorption of polyacrylic acid polymers. This promotes the interaction between core and shell particles. Nanoparticles added subsequently to the core suspension hence coat on core particles by both electrostatic and polymer bridging mechanisms. Success of the process depends to a large extent on the absence of homoflocculation of nanoparticles. Coating itself is estimated by monitoring change in the zeta potential of core-shell structure. The coating scheme as well as the characterization of these nanocomposite particles will be discussed in this talk. This processing scheme makes it simpler for preparation of both bulk and surface coating of nanostructured materials using these engineered particles as building blocks.

4:15 PM FF4.7 
BINARY SELF-ASSEMBLED MONOLAYERS FOR SURFACE CONTROL OF LIQUID-CRYSTAL ORIENTATION: AN X-RAY STUDY. Robert E. Geer, Univ at Albany, SUNY, Dept of Physics, Albany, NY; Jean Y. Yang and Curtis W. Frank, Stanford Univ, Dept of Chemical Engineering, Stanford, CA.

Simultaneous chemisorption of ultrathin (1.2 nm) alkylsilane and chromophore-tethered alkylsilane monolayer films to silicon oxide surfaces have been performed in order to control and tailor the surface energy for substrate alignment of liquid-crystalline mesogens for electro-optic devices. The systems under investigation consist of (1) naphthalene terminated undecyltrichlorosilane and decyltrichlorosilane and (2) naphthalene terminated undecyltrichlorosilane and octadecyltrichlorosilane simultaneously chemisorbed to the native oxide of silicon wafer (001) and conventional float glass substrates. Detailed x-ray reflectance from these monolayers is used to reconstruct the electron density profile of the monolayer films and the associated roughness at the air/monolayer and monolayer/silicon oxide interfaces. This analysis reveals the napthyl chromophore orientation in mixed and pure monolayers for both systems. Characterization of the off-specular diffuse x-ray scattering is also discussed with respect to conformality of the modified silicon oxide surfaces. These measurements are correlated with observed orientational alignment effects of nematic liquid crystals on float glass.

4:30 PM FF4.8 
NANOSCALE CONTROL OF MOLECULAR ORGANIZATION IN LANGMUIR-BLODGETT FILMS OF PORPHYRIN DERIVATIVES. Claudia Nicolae, Paolo Facci, Marco P. Fontana, University of Parma, Physics Department and Istituto Nazionale per la Fisica della Materia, Parma, ITALY; Enrico Dal Canale, University of Parma, Chemistry Dapartment, Parma, ITALY.

In this paper we present a study of molecular self-organization in Langmuir-Blodgett monolayers deposited from different points in the compression isotherm of the Langmuir monolayer on the aqueous subphase. The deposited molecules were porphyrin rings to which alkyl tails of different number of carbon atoms had been attached. Such molecules yield liquid-crystalline columnar phases in the bulk. The interplay between the mesogenic potential and the forces at the air-water interface can be used to control the molecular aggregation and its time development once the molecules are deposited onto a solid substrate. Such control is achieved by depositing from different zones of the compression isotherm. In particular, AFM microscopy at molecular resolution shows the typical columnar arragement of edge-on rings if deposition was made at the high pressure of the pseudo-solid phase. If instead molecules are deposited from the coexistence part of the isotherm, a hyerarchy of superstructures develops in the solid monolayer, depending on the point of the isotherm at which deposition was made. Such superstructures span the dimension range from nanometers to microns as observed by AFM imaging. Our results have been confirmed by optical absorption measurements. Finally, the study of the influence of the length of the lateral alkyl chains on such phenomena indicates that molecular orientation is strongly influenced by such length.

4:45 PM FF4.9 
STUDY OF SURFACTANT INDUCED SILVER CRYSTAL GROWTH USING X-RAY AND ELECTRON SCATTERING. Z. Li, Exxon Research and Engineering Company, Annandale, NJ; Y.D. Kim, M.W. Kim, Dept of Materials Science, KAIST, Seoul, SOUTH KOREA; Y.T. Kim, Dept of Chemistry, University of Alabama, Tuscaloosa, AL; and M.H. Rafailovich, J. Sokolov, Dept of Materials Science and Engineering, SUNY at Stony Brook, Stony Brook, NY.

Self-assembled surfactant monolayer of alkanethiols at the air water interface were used to induce growing thin layer of silver crystals by adding AgNO3 into the water subphase. In-situ x-ray reflectivity and in- Lane diffuse scattering were performed using Langmuir-Blodgett technique, and transmission electron microscopy (TEM) was used to study the Langmuir-Blodgett dry film transferred onto silicon covered copper grids. The silver layer were found to quickly assemble at the thigh water interface and the stabilized thickness were ca 40. This silver layer thickness may be defined by the silver salt concentration added into the water subphase. The crystal domains were found on the TEM grids to be around a few microns and their boundaries showed clearly 6 fold symmetry. Well defined diffraction pattern with 6 fold symmetry gave a reciprocal lattice spacing of 2.39. A crystal layer of silver was therefore confirmed and the surface orientation is strongly associated with the surfactant monolayer interface with water, due to the formation of silver thiolate. The crystal structure will be discussed in comparison with the bulk.

SESSION FF5: POSTER SESSION 
Chair: Lhadi Merhari 
Tuesday Evening, December 2, 1997 
8:00 P.M. 
America Ballroom (W)

FF5.1 
NANOSIZED OXIDE POWDERS VIA FLAME SPRAY PYROLYSIS: SYNTHESIS, CHARACTERIZATION, AND MICROSTRUCTURAL EVOLUTION. R. Baranwal, T.R. Hinklin, R.M. Laine, University of Michigan, Dept. of Materials Science and Engineering, Ann Arbor, MI.

We recently described methods of producing nanosized oxide powders by flame spray pyrolysis of novel alkoxide and double alkoxide aluminate and silicate complexes. This scaleable synthesis route provides reproducible, high purity nanosized powders. For example, we can make crystalline mullite (3Al2032SiO2) powders with particle sizes of 2-200 nm (ave. = 75 nm) and surface areas = 40-60 m2/g at production rates 250 g/h. Single crystal TiO2 powders can be produced with particle sizes 2-70 nm (ave. = 50 nm) and surface areas of 60-80 m2/g. Single crystal CeO2 powders can be produced with ave. particle size = 75 nm. The powders are characterized using TGA, DTA, FTIR, BET surface area, gas sorption, SEM, and TEM techniques. This presentation will focus on the compaction and sintering behavior of some of the aforementioned nanosized powders. After sintering (1000- 1600C), submicron grain sizes are retained. Characterization of the sintered compacts will also be discussed.

FF5.2 
SYNTHESIS OF FERRIC OXIDE NANOPARTICLES BY VAPORIZATION OF IRON PENTACARBONYL. Mark Dudley, Institute of Materials Science, University of Connecticut, Storrs, CT.

Amorphous Ferric Oxide particles of 3 to 10 nm size can be synthesized by vaporizing and oxidizing iron pentacarbonyl. Nitrogen gas at ambient temperature is flowed through a gas washing bottle containing liquid iron pentacarbonyl. The vapor is combined with a hot air stream and drawn through an electrostatic precipitator where the ferric oxide is collected. Oxidation at a relatively low temperature within an airstream yields a product that is finely separated and very pure, with average particle size under 10 nm. Bulk density is less than 0.05 g/ml and specific surface area greater than 250 m2/g. The globular shape of the particles offers an improvement in compounding over typically rod-shaped conventional ferric oxide powders. The microsurface is heavily covered with crystal lattice defects, enhancing catalytic properties. The product is suitable for cracking, synthesis and as a solid fuel rocket propellant catalyst.

FF5.3 
RHEOLOGICAL BEHAVIOR OF AN ALUMINUM NITRIDE NANOPARTICLE SUSPENSION IN POLY(AMIC ACID)-NMP SYSTEM. Xiaohe Chen, Kenneth E. Gonsalves, Department of Chemistry and Institute of Materials Science, University of Connecticut, Storrs, CT; R.S. Rounds, Fluid Dynamics, Inc., Piscataway, NJ.

Preliminary rheological characterizations of aluminum nitride (AlN) nanoparticle suspensions in nonaqueous Newtonian fluid media, NMP and NMP/poly(amic acid) solutions, reveal marked differences in viscoelastic behavior, at relative low dispersed phase volume fractions. Dynamic mechanical and steady shear measurements provide experimental evidence of the effective interparticle and polymer/particle interactions in a dispersion process of non-oxide nanoparticles for ceramic/polymer nanocomposites. The rheological nature of the nanoparticle suspensions corresponds to interparticle physiochemical interactions that have been previously concluded and discussed.

FF5.4 
POLY (STYRENE-b-BUTADIENE-b-STYRENE) SELF-ORGANIZED ULTRATHIN FILMS. Dayang Wang, Fengqi Liu, Yu Bai Bai, Zhiqiang Liu Dongfang Shen, Tiejin Li, Xinyi Tang, Jilin Univ, Dept of Chemistry, Changchun 130023, P.R.CHINA; Jiaqing Song, Zhongfan Liu, Beijing Univ, College of Chemistry and Molecular Engineering, Beijing, P.R. CHINA.

Direct images of the surface morphology of a series of the poly(styrene-b-butadiene-b-styene)(SBS) ultrathin films have been obtained with the atomic force microscopy(AFM). The resulting films consist of 25 nm-diameter spherical structures and/or 25 nm-width cylindrucal structures.In consideration of the composition of SBS used in this work, these structures are surprisingly different from alternative-lamellar structures which should be formed under nearly equilibrium conditions . This indicates these structures depend on the property of the solvent used and the selectively for the components of the block copolymer at the interfaces of the ultrathin solution layer on substrate (the upper air-liquid interface and the lower solid-liquid interface). The film was formed under kinetic control.

FF5.5 
ASSEMBLY OF POLYMER MICROSPHERES AND THE THIN-FILM MICROPATTERNING. Hui Du, Fengqi Liu, Xinyi Tang,Yu Bai Bai,Tiejin Li, Jilin University, Department of Chemistry, Changchun, Jilin, CHINA.

Copolymer latexes of poly(styrene/acrylic acid)with diameters of 80nm and 300nm were closely packed into two-dimensional arrays respectively on glass,mica and silicon substrates. Since the latexes were negtively charged due to -SO4- and -COOH groups on the surface, their film formation, in some degree, was affected by the electrostatic interaction between two particles as well as capillary force. Different electrolytes were added into the colloid to adjust the particle interaction so that the attractive and repulsive forces were properly balanced and the ordered arrays were achieved. Thin metal film was deposited on the latex monolayer by thermal evaporation in vacuum. Finally, the spheres were dissolved away to leave behind a surface with features located where the interstitial spaces of the densely packed spheres. Different patterns of continuous grid, separate islands and dots can be obtained through controlling the treatment time and intensity. This work would be significant in nano-structured electronics.

FF5.6 
TUNNELING SPECTROSCOPY ON TWO-DIMENSIONAL ARRANGEMENTS OF METAL CLUSTERS AT ROOM TEMPERATURE. R. Houbertz, Th. Feigenspan, U. Weber, U.E. Volmar and U. Hartmann, Institute of Experimental Physics, University of Saarbrücken, Saarbrücken, GERMANY.

Scanning tunneling spectroscopy (STS) was used to investigate the local electronic structure of ligand-stabilized Au55 cluster agglomerates at room temperature in ultra high vacuum (UHV) as well as under ambient conditions. The Au55 clusters were deposited onto highly oriented pyrolitic graphite (HOPG) substrates from a solution containing Au55 clusters. The resulting morphologies can be adjusted by varying the concentration of the cluster solution. After evaporation of the solvent, the samples were transfered immediately into the instrument. The STS measurements were performed on thick Au55 cluster layers as well as on small Au55 cluster islands. For all types of sample, the I(V) curves show a nonlinear behavior. Step-like structures develop in the I(V) curves for decreasing layer thickness. The staircase can be attributed to single electron tunneling (SET) within a series of small tunnel junctions involving only one or two Au55 clusters as center electrodes. These results are supported by Monte Carlo simulations as well as by a determination of the threshold voltages within the I(V) curves, calculated using an analytical approach in the framework of a semiclassical theory.

FF5.7 
CONTROLLING THE SURFACE CLEANINESS OF NANOSTRUCTURED ALPHA-IRON AND M50 TYPE STEEL (Fe-Cr-Mo-V-C) POWDERS. Stephan Schady, Chi Law, Pratt & Whitney Materials, East Hartford, CT; Maurice Gell, Ken Gonsalves, John Morral, Sri Prakash Rangarajan, University of Connecticut Institute of Materials Science, Storrs, CT.

The cleaning effectiveness of the hydriding process to remove oxygen (adsorbed and metal oxide) and carbon (elemental, carbides, and carbon hydrogen complex) from the surface of nanostructured alpha-iron and M50 type steel (Fe-Cr-Mo-V-C) alloy powders was investigated. The hydrogen treated powders and consolidated material were examined by X-ray dispersive spectroscopy, bulk chemical analysis, metallographic examination, and mechanical property testing. The trends in the cleaning effectiveness compared favorably with predictions from Richardson and Jeffes plots of metal-metal oxide equilibria.

FF5.8 
OPTICAL PROPERTIES OF GOLD CLUSTERS PRECIPITATED ON ZIRCONIA PARTICLES. J. -C. Valmalette, L. Lemaire, G. L. Hornyak, J. Dutta and H. Hofmann, Powder Technology Laboratory, Department of Materials Science, Swiss Federal Institute of Technology (EPFL), Lausanne, SWITZERLAND.

Clusters or fine metallic particles deposits on ceramic powders are of great interest in the domain of catalysis and may also have promissing applications in microelectronics due to the inherent non-linear electronic and optical properties. However, the controlled synthesis of these nano-structured materials need proper understanding of the chemical reactions. We have studied precipitation of noble metals with a viewpoint of extending these synthetic processes to other metals. Here we will discuss the synthesis of gold clusters on the surface of the oxide fine particles (in the range 60-100nm). The influence of pH of the solution, the concentration of metal and the reducing agent will be discussed. The size distribution of the precipitated gold clusters, determined by electron microscopy, are around 2 -10 nm. The interface between the gold clusters and oxide has been investigated by HRTEM. Optical measurements of the zirconia supported gold clusters shows a significant shift of the plasmon resonance. A model based on effective medium theory is proposed taking in accompt the high refractive index of zirconia.

FF5.9 
NANOSCALE COPPER SULFIDE MATERIALS FOR NEAR INFRARED NONLINEAR OPTICAL DEVICES. K.V. Yumashev, A.M. Malyarevich, N.N. Posnov, P.V. Prokoshin, V.P. Mikhailov, International Laser Center, Minsk, BELARUS; V.S. Gurin, Physico-Chemical Research Institute, Minsk, BELARUS.

Nanometer size semiconductor crystals have been extensively studied recently because, in addition to the fundamental interest in materials science, they have been used as nonlinear optical devices. The presence of the nanocrystal surface as a boundary and source of surface states makes optical properties of nanometer-sized crystals highly sensitive to chemical treatment of ones. In this presentation, we report the results of luminescence and picosecond pump-probe measurements on CuS, CuFeS2, and CuInS2 nanocrystals (NC's) with oxidized surface. The oxidized and usual CuS, CuFeS2, and CuInS2 NC's samples used in this study had a mean nanocrystal radius of 3-5 nm. Oxidation of copper sulfide containing NC's leads to the appearance of broad absorption band with the maximum at 1 - 1.2 m. Picosecond laser pulses induce bleaching of this band in the oxidized NC's and induced absorption in the visible range. The fast-decayed (50 ps) and long-lived (500 ps) induced absorption have been observed. The pump-probe and luminescence results lead us to propose an energy level diagram for oxidized NC's. It demonstrates the additional level in the middle of the band gap (the 1 - 1.2 m absorption is supposed to originate from this level) and trapping levels near the bottom of the conduction band. The origin of additional absorption band which appears in NC's after oxidation and is attributed to charge transfer between CUI and CUII and kinetics of bleaching of near IR absorption band and induced absorption from trapping levels are discussed.

FF5.10 
INCORPORATION OF NANO-PARTICLE SITES IN POLYMER MATRIX BY METAL ION IMPRINTING. Alok Singh, Eddie L. Chang, Dhananjay Puranik, Yan Gao; Laboratory for Molecular Interfacial Interactions, Naval Research Laboratory, Washington, DC.

An approach is presented to synthesize polymer matrix that allows incorpoartion of metal ions reversibly and selectively. Linear chain triethylene tetramine modified with a polymerizable functionality have been employedin the formation of complexes with selected metal ions. Unlike cyclic ligands, linear ligating molecules demonstrate more freedom to achieve metal-ion dependent size and geometry of the complex. The resulting complex is then crosslinked with matrix monomer consisting of either methacrylate or styryl group to provide a rigid polymer matrix which has shown selectivity towards the metal ion. Realtively smaller size of metal ions facilitated their easy accessability to the imprinted sites in the polymers. Polymeric materials doped with metal nanoparticles and metal ions have been investigated for their electronic properties.

FF5.11 
PREPARATION AND CHARACTERIZATION OF SiO2/Au NANOCOMPOSITE BY R.F. SPUTTERING. Shinya Terauchi, Hiroyuki Umehara, Naoto Koshizaki, Takeshi Sasaki, National Institute of Materials and Chemical Research, Tsukuba, JAPAN.

Previously we reported the preparation of Au nanoparticles by r.f. magnetron sputtering technique[1]. Formation of Au nanoparticles on carbon film substrate occurred at room temperature for the sputtering pressure mTorr. Their size was varied from 3 to 12 nm by changing the sputtering pressure and the r.f. input power. The average size of Au nanoparticles increased with increasing the r.f. power and decreased with increasing sputtering gas pressure. In present work, we tried to fabricate SiO2/Au nanocomposites by alternate sputtering method. The size of the Au particles seem to be unchanged by the SiO2 sputtering and well controllable by the sputtering parameters. The nanoparticles in SiO2 were observed by TEM and the nanocomposites were characterized by XPS technique. TEM observation revealed the size of Au nanoparticles 2-15 nm. From XPS study, a chemical shift of the Au4f peak was observed.

FF5.12 
DETAILED STUDY ON THE CHARACTERIZATION OF Ag NANOCLUSTER IN POLY(METHYL METHACRYLATE). Naohisa Yanagihara, Toru Hara, Kazutaka Uchida and Miyuki Wakabayashi, Dept. of Material Science and Engineering, Teikyo Univ., Utsunomiya, JAPAN.

Today's attention in nanoclusters is seems to be focused on the preparation of well characterized and stable transition metal nanoclusters of narrow size distribution, since such metal clusters are of considerable scientific as well as technological importance. In particularly, organic polymers containing ultra fine metal particles are considered to be highly functionalized materials, since they are one of the most promising materials for the nonlinear optical devices. Although there are a few exceptions, in almost all cases of the preparative methods, the metal particles are traditionally obtained by chemical reduction of simple metal salts. In contrast to these usual procedures, Nakao[1] has found a novel method for preparing metal solid sols in poly(methyl methacrylate) (PMMA), which contain noble metal clusters such as palladium, platinum, silver and gold. However, in this procedure, what is peculiar is that metal ions are reduced to zero valent metal clusters without any specific reducing agents. It was decided, therefore, to investigate in detail the preparation and characterization of Ag cluster in PMMA (Ag/PMMA), in order to reveal the chemical species that can act as a reducing agent. In this presentation we introduce the detailed characterizations of Ag/PMMA samples, which have been prepared by widely varying the initial concentrations of Ag complex and radical initiator, and the duration of the heat treatment, and which have obtained by UV and TEM measurements. Moreover, a kinetic study on the polymerization of MMA in the presence of Ag complex will be discussed, and a mechanism for the formation of Ag cluster in PMMA will be elucidated.

FF5.13 
SYNTHESIS AND MAGNETO-OPTICAL PROPERTIES OF NANOSTRUCTURED IRON/PMMA COMPOSITE. K.E. Gonsalves, G. Carlson, Polymer Program, Institute of Materials Science and Department of Chemistry, University of Connecticut, Storrs, CT; M. Benaissa, M. José-Yacamàn, Instituto de Fisica, Universidad Nacional Autonoma de Mexico, MEXICO; D.Y. Kim , J. Kumar, Center for Advanced Materials, Departments of Physics and Chemistry, University of Massachusetts, Lowell, MA.

There has recently been much interest in the chemical synthesis of nanostructured materials. This approach has the advantages of improved mixing, better control of stoichiometry, and tailored synthesis by assembly of atomic or molecular precursors. It is of interest to examine the possibility of using nanoparticles of iron and iron oxide in a polymer matrix for use as a Faraday rotator. The possibility of a polymeric Faraday rotator using nanoparticles which can be molded or cast into rods without the expense of crystal growth and polishing is very attractive. Particles of alpha iron of 2-10 nm size were prepared by thermal decomposition of Fe(CO)5 in decalin solution. This material was stabilized by coordination of the surface with dodecanethiol. Methyl methacrylate was added, along with azobisisobutyronitrile, an initiator. This mixture was polymerized by heating at 72C for two hours to create the poly(methyl methacrylate) matrix. The composite was characterized using high resolution transmission electron microscopy. Symmetry analysis and measurement of the lattice fringe spacings in the HRTEM image indicate that the particle is alpha-Fe (BCC) observed along the <001> zone axis. Particles show flat surfaces, terminating with {110} facets. This seems reasonable, since the (110) planes are most dense in a BCC lattice, which makes them very stable. The magnetic susceptibility of the composite material was measured in a Guoy susceptibility balance at room temperature and found to be 1.2x10-5 esu. The optical Faraday rotation of the polymer composite, measured at 633 nm was approximately l.2 deg/Tesla. The Verdet constant measured by the Faraday rotation of the polymer composite at 633 nm is 0.36 min/Oersted cm.

FF5.14 
KINETIC MODELING OF SURFACE-FUNCTIONALIZATION IN NANOSTRUCTURED GOLD. K.E. Gonsalves, G. Carlson, Polymer Program, Institute of Materials Science and Department of Chemistry, University of Connecticut, Storrs, CT; J. Ascencio Gutierrez, Instituto Nacional de Investigaciones, Nucleares, Carretara Mexico-Toluca, Salazar, MEXICO.

Alkanethiols adsorb spontaneously onto gold, forming a dense monolayer with the alkyl chains in an all-trans configuration tilted at 30 to the surface normal. This gold/thiol affinity has been the basis for the chemical synthesis of stable nanoparticulate gold. The particles were prepared using a phase-transfer catalyzed reduction of a gold salt in the presence of unbranched alkanethiols. The competition or the gold/thiol coordination process with nucleation and crystal growth of atomic gold results in nanoparticules with alkyl groups tethered to the surface by sulfhydryl groups. The steric stabilization introduced by these alkyl groups prevents particle coalescence. The number density of alkyl groups necessary to impart stability varies with the length of the group. To study this effect, gold nanoparticles stabilized by unbranched alkanethiols with eight, twelve, and sixteen carbons were prepared. (There was no yield of nanoparticles from a reaction run with butanethiol.) Analysis of TEM images was used to determine the particle size and size distribution. The C8 and C12 products were very similar, having a diameter of 2 1.2 nm. However, the C12 reaction gave a much higher yield (75%, compared to 36% for C8). The C16 yield was 68%. However, this product had a larger, more disperse particle size distribution: 4.4 3. 1 nm. Models based on TGA data and HRTEM images of the products indicate that 24% of the gold atoms in the C8 and C12 products were at a particle surface, while only 10% were at the surface in the C16. The surface coverage per alkanethiol molecule was 6.7 Å2 and 8.4 Å2 for C8 and C12, respectively, compared to 21 Å2 observed in monolayers assembled on flat surfaces. The possible configurations taken on by the tethered alkanethiol groups was modelled using Cerius software. Results of these simulations will also be presented.

FF5.15 
DRIFTS SURFACE CHARACTERIZATION OF ZINCBLENDE NANOSTRUCTURED GaN. K.E. Gonsalves, G. Carlson, Polymer Program, Institute of Materials Science and Department of Chemistry, University of Connecticut, Storrs, CT; M.-I. Baraton, University of Limoges, Limoges, FRANCE.

There has recently been much interest in binary III-V materials such as gallium nitride (GaN) due to their wide, direct bandgap energy (3.1 - 3.8 eV). In order to control the bandgap and optical properties, it is desirable to have small particles of controlled size. Recently, de-agglomeration of a nanostructured powder, with dispersion of the solid phase into a poly(methyl methacrylate) matrix has yielded nanocomposites with novel optical properties. To understand the surface chemistry of particle de-agglomeration and stabilization, a study of the powder was undertaken using diffuse-reflectance infrared Fourier transform spectroscopy (DRIFTS). The DR apparatus (Graseby-Specac) included an environmental chamber with a ZnSe window. The chamber's temperature can be controlled up to 500C and it can be subjected to vacuum or treated with gases at controlled pressure. It was not possible to use methyl methacrylate as a probe molecule, since it would polymerize in the temperature range of the study and damage the instrument. To model the functionalities of MMA, ethyl acetate, acetone, and acetic acid were used. Deuterium exchange was also studied to determine the locations (surface vs. the bulk core) of the particle functionalities. By comparing the DRIFTS spectra of the powder before and after adsorption of the various molecules, a model of the surface chemistry was derived having the following features: i) a particle core with dangling bonds passivated by hydrogen, creating Ga-H and N-H groups, ii) a particle surface with predominantly NH2 and OH groups, with N-H and Ga3+ groups in lesser amounts. Thus, the particles are stabilized by adsorption of MMA onto a surface NH or OH through the acetate functionality, with elimination of methanol. In the final processing step, these adsorbed MMAs polymerize at their double bonds, binding to the polymer matrix.

FF5.16 
SYNTHESIS AND MAGNETIC PROPERTIES OF DISPERSED AND COATED -Fe2O3 NANOPARTICLES. Lorenza Suber, Dino Fiorani, Antoni Garcia Santiago, CNR, Inst of Materials Chemistry, Roma, ITALY; Massimo Angiolini, Amelia Montone, ENEA, Dept. Innovazione, Roma, ITALY.

Antiferromagnetic nanoparticles have been receiving a growing attention in the last few years, due to still open questions about their fundamental magnetic properties and to their potential for exhibiting magnetization reversal by quantum tunneling. We have prepared and studied the magnetic properties of rhombohedral, acicular and spherical -Fe2O3 nanoparticles 1 and now, dispersing them in a non magnetic matrix or coating the particles with polypyrrole or silica layers, we have investigated the effect of interparticle interactions. By varying the degree of dispersion or the thickness of the coating layer we were able to tune the interparticle interaction strength. Morphological, structural and microanalytical aspects were examined by X-ray powder diffraction and TEM analyses. The magnetic measurements performed by a commercial SQUID magnetometer evidenced a lowering of the blocking temperature (TB) coercive field (Hc) and remanent magnetization (Mr) with increasing interparticle distance.

FF5.17 
THERMAL PLASMA SYNTHESIS OF COATED SOFT MAGNETIC NANOCOMPOSITES. John Henry J. Scott, Dept of Physics, Carnegie Mellon Univ, Pittsburgh, PA; Zafer Turgut, Michael E. McHenry, Dept of Mat Sci and Engr, Carnegie Mellon Univ, Pittsburgh, PA; Sara A. Majetich, Dept of Physics, Carnegie Mellon Univ, Pittsburgh, PA.

Advanced aerospace applications need soft magnetic materials capable of operating at in-service temperatures approaching 600C. Additional requirements include very high saturation magnetization, high electrical resistivity, and low hysteretic losses. Although no existing material displays this demanding combination of properties, magnetic nanocomposites show promise for meeting these needs if their unique microstructure can be maintained during processing and operating conditions.

8:30 AM *FF6.1 
WET-CHEMICAL ROUTES TO IMPROVE PARTICLE PERFORMANCE THROUGH SURFACE MODIFICATION. Richard Partch, Department of Chemistry and Center for Advanced Materials Processing, Clarkson University, Potsdam, NY.

Advances in materials performance requires that individual components from which they are made meet new chemical and physical specifications, and that interfacial phenomena between phases be better understood. The latter become dominant when particles to be dispersed in a matrix or onto a substrate are less than 100 nm in size. Increased interest in employing nanoparticles in manufacturing dictates that efforts be expanded to control their colloidal properties. Studies in particle technology by the author have focused on application of wet-chemical reaction methods for forming functionalized surfaces on microparticles having different shapes and compositions. Control of nucleation, growth, polymerization, wetting and adhesion of the coating material being generated in situ have been evaluated. The synthetic methods developed should be applicable to new nanoparticle systems and help achieve as yet unrealized particle-matrix compatibility. This paper will summarize how and why several different microparticle powders were studied and some boundary conditions on reactions carried out on dispersions containing nanoparticles.

9:00 AM FF6.2 
INFLUENCE OF SURFACE SILANOL STRUCTURE AND HYDRATION FORCES ON ALKOXIDE-DERIVED SILICA GEL STRUCTURE. Kamiya Hidehiro, Mitsui Mika, Miyazawa Sakura, Takano Hideo, Horio Masayuki, Tokyo University of Agriculture and Technology, Graduate School of Bio-Application and System Engineering,Tokyo, JAPAN.

By using alkoxide-derived silica gels with various preparation conditions, the effects of the surface silanol structure and interaction force between solid surfaces in water on the gel structure. The preparation conditions for silica gels were focused on the amount and difference of catalysts (acid or base) , H2O/TEOS mole ratios and primary sol diameter. Surface silanol structure and interaction between particles were determined by a FT-nIR, FT-IR and Atomic Force Microscope (AFM), respectively. Gel micro-structures and pore size distribution were investigated by using a mercury porosimetry. As results, when the acid catalysed hydrolysis and relatively low H2O/TEOS mole ratio ( from 4 to 10) were used, surface silanol was almost hydrogen bonded silanol, and isolated silanol was disappeared. Since these hydrogen bonded silanol formed a hydrogen bonded water layer on silica surface, the additional hydration force appeared strongly between solid surface. On the contrary, the surface density of isolated silanol increased with increasing H2O/TEOS mole ratio or decreasing primary particle diameter, the additional hydration force between ultra fine powder disappeared. When these additional hydration force acted on silica surface, mean pore size decreased and gel density increased. During gel formation process, the additional hydration force protect to form porous aggregates structure and promote to produce the uniform and dense gel structure.

9:15 AM FF6.3 
BLOCK COPOLYMER MONOLAYERS AT SURFACES. Randall Saunders, Michael Kent, James Small, Sandia National Laboratories, Albuquerque, NM.

Monolayers on surfaces have become a topic of considerable interest over the last few years. This has arisen from the need to functionalize a surface so that its properties are different than the properties of the bulk material. Our research has initially involved functionalizing copper and glass surfaces to enhance their adhesion with epoxy. We have accomplished this using block copolymers made by Ring-Opening Metathesis Polymerization (ROMP). We use this approach because the catalyst used to make the polymers polymerizes the monomers in a living fashion and tolerates a wide variety of chemical functionalities. In this presentation we will discuss the synthesis and characterization of these block copolymers, including NMR, GPC, SAXS, and SANS. We will discuss the fact that when one block is designed to adhere to the designated surface, ordered monolayers can result, which are confirmed by time-of-flight SIMS and neutron reflectivity experiments. We will also discuss a generalization of this approach to other surfaces and other applications such as corrosion resistance, and sensors. Finally we will also compare and contrast pros and cons of this technique compared to the self-assembled monolayer techniques.

9:30 AM FF6.4 
ANALYSIS OF HETERO-COAGULATION STRUCTURE OF COLLOIDAL MULLITE PRECURSOR POWDER -EXPERIMENTAL APPROACH AND COMPUTER SIMULATION. Cho Yong-Ick, Kamiya Hidehiro, Takano Hideo, Horio Masayuki, Tokyo University of Agriculture and Technology, Graduate School of Bio-Application and System Engineering,Tokyo, JAPAN; Hisao Suzuki, Shizuoka University, Dept of Materials Science, Shizuoka, JAPAN.

To control the hetero-coagulation structure of ultra-fine gamma-alumina and silica powder for mullite ceramics, the hetero-coagulation structures in suspensions with different pH conditions were investigated by the experimental approach and computer simulation. The electrophoretic mobility distribution, which was determined by a Laser Doppler method, was used for the estimation of hetero-coagulation structure. As results, when precursor powders were prepared by colloidal mixing processes at pH=10.3, a bimodal electrophoretic mobility distribution was observed. Since each peak almost corresponded to the electrophoretic mobility of gamma-alumina or silica particle, hetero coagulation did not be formed in suspension. In the case of pH=6, weak hetero-coagulates patterned in suspension, however, unstoichiometric and large aggregates were formed in suspension. Since narrow and single mode electrophoretic mobility distribution was observed at pH=4.4, the uniform and stoichiometric hetero-coagulates for mullite precursor powders were obtained. The change of hetero-coagulation structure with different pH conditions were analyzed by using the calculated value of the maximum repulsive potential barrier between gamma-alumina and silica or gamma-alumina based on DLVO theory. Furthermore, Brownian dynamic methods were applied on the analysis of hetero-coagulation structure at different pH conditions.

9:45 AM FF6.5 
STABILIZATION AND TRANSFORMATION OF THE PHASES IN NANOSTRUCTURED ZIRCONIA PREPARED BY CHEMICAL METHODS. A. Garcia-Ruiz*, UPIICSA-National Polytechnical Institute (IPN), Academy of Physics, Resina, Mexico, MEXICO; T. D. Xiao, University of Connecticut, Precision Manufacturing Center (PMC), Storrs, CT; A. Morales, X. Bokhimi, Institute of Physics, The National University of Mexico (UNAM), Mexico, MEXICO.*COFAA-IPN's Fellow.

We discuss the stabilization of the cubic and tetragonal phases and their transformation into the monoclinic phase in nanocrystalline zirconia prepared by chemical methods. We consider two cases: non doped zirconia and when it is doped with yttria. We analize the relationship between the local order of the amorphous phase, which is precursor of the nanocrystalline phases, and the crystalline phases. The formation of the cubic and tetragonal phases was related to the dehydroxilation of their precursors. In the undoped samples, the transformation of the tetragonal nanophase into the monoclinic one was also related to dehydroxilation of the sample. This result does not support the claims reported in the literature which assume that the transformation of the nanocrystalline tetragonal phase into monoclinic zirconia is caused by stress accumulation during crystal growing.

10:00 AM FF6.6 
MICROSCOPIC ROLE OF A SURFACTANT IN EPITAXIAL CRYSTAL GROWTH. Seung Mi Lee+ and Young Hee Lee, Department of Physics, +Department of Semiconductor Science and Technology, and Semiconductor Physics Research Center, Jeonbuk National University, Jeonju, Jeonbuk, SOUTH KOREA.

Despite the fact that a surfactant has often beeen introduced in epitaxial crystal growth, its microscopic role on energetics and kinetics is still far from being clearly understood. We study group V and H surfactants in Si/Ge systems. In particular, H atom has much smaller size than the host materials but still acts like a surfactant in many experimental observations. We introduce in this study the first principles calculations to investigate the microscopic role of H as a surfactant. We find H to be significantly different from group V surfactants in many ways of adsorption, diffusion, and exchange processes. Similarities and differences are further discussed by comparing with recently observed experimental results.

10:45 AM *FF6.7 
SURFACE-CONTROLLED NANOSPHERES AS BLOOD PERSISTENT DRUG CARRIERS. R. Gref, P. Quellec, E. Dellacherie, ENSIC, Laboratoire de Chimie Physique Macromoléculaire, Nancy, FRANCE; M.J. Alonso, Universidad de Santiago, Laboratorio de Farmacia Galénica, Santiago de Compostella, SPAIN.

Blood persistent nanospheres have important therapeutic applications; they can be used as injectable reservoir systems able to deliver drugs directly in the blood stream, for targeting drugs to specific sites of action, or for medical imaging. However, injected nanospheres are generally eliminated by the reticulo-endothelial system within minutes after administration. To obtain a coating that might prevent opsonization and subsequent uptake by phagocytic cells, we prepared sterically stabilized nanospheres using diblock copolymers. The nanospheres are composed of a hydrophilic polyethylene glycol (PEG) coating, in a brush configuration, and a hydrophobic biodegradable poly (lactic acid) (PLA) core in which various drugs can be entrapped. They were prepared from oil-in-water emulsions using PEG-PLA copolymers soluble either in the organic phase or in the aqueous phase. In the latter case, the hydrophobic PLA anchor ensures the stability of the PEG coating after solvent evaporation. We studied the surface properties of the nanospheres coated with PEG 2 to 20 KDa, at different surface densities, in order to choose an optimal PEG coating brush, needed to reduce the surface charge, avoid plasma protein adsorption, minimize the interaction with phagocytic cells, and thus prolongate the blood circulation time. To explore the therapeutic applications of this type of nanospheres, we entrapped albumin, a model protein, inside particles of less than 200 nm, with high efficiencies and loadings. Studies of protein localization in the matrix before and during release (surface analysis, freeze fracture, surface charge measurements, etc), PEG detachment and polymer degradation, were carried out. The release was controlled by an appropriate choice of the polymers or blends forming the matrix.

11:15 AM *FF6.8 
FUNCTIONAL DNA/NANOPARTICLE-BASED MATERIALS. Robert Elghanian, James J. Storhoff, Robert C. Mucic, Robert L. Letsinger, Chad A. Mirkin, Northwestern University, Department of Chemistry, Evanston, IL.

A variety of methods have been developed for assembling metal and semiconductor colloidal particles into materials with technologically and fundamentally important applications. A new DNA-based method for organizing colloidal nanoparticles into macroscopic aggregate structures, which functions as a selective DNA detection system, is presented. This method involves the modification of 13 nanometer diameter gold particles with thiol-oligonucleotides which recognize complementary polynucleotides in solution leading to the formation of macroscopic aggregates. The formation of the aggregates decreases the interparticle distance, causing the color of the colloidal solution to change from red to blue. We have shown that this color change is sequence-specific and that we can use this selectivity to colorimetrically differentiate polynucleotide sequences on a solid-state support. The preparation of DNA-modified nanoparticles, the assembly of these nanoparticles into macroscopic aggregate structures, the characterization of the resulting aggregates, and the ability of the aggregation process to function as a sequence-specific DNA sensor will be presented.

11:45 AM FF6.9 
SYNTHESIS AND SURFACE CHARACTERIZATION OF FUNCTIONALIZED POLYLACTIDE COPOLYMER MICROPARTICLES. Kenneth E. Gonsalves, Shuhua Jin, Department of Chemistry & Polymer Program at the Institute of Materials Science, University of Connecticut, Storrs, CT; Marie Isabelle Baraton, LMCTS URA320 CNRS, University of Limoges, Limoges, FRANCE.

Microparticles of poly(lactide) (PLac) and its copolymers with the amino acids, serine (P(Lac-Ser)), and aspartic acid (P(Lac Asp)), respectively, were synthesized using the solvent evaporaion microemulsion technique. Poly(vinyl alcohol) (PVA) was added as a non-ionic surfactant to stabilize the particles. The particle sizes are in the range of 200 nm. The surface of the particles was characterized by FTIR transmssion spectoscopy under evacuation at room temperature and at 200C. Hydroxy groups originating from PVA exist on the surfaces of the particles and they were observed at 3506 cm-1 . Free hydroxy groups onginating from the serine residue pendant to the copolymer P(Lac-Ser) backbone were observed at 3476 cm-1. Also, free carboxylic acid groups pendant to the copolymer P(Lac-Asp) backbone, originating from the asparic acid residue, were observed at 3387 cm-1. The appearance of the free hydroxy or carboxylic acid groups in the IR spectra also showed that these hydrophilic functional groups moved to the surface of the particles during the process of microemulsion.

SESSION FF7: SINTERING AND FUTURE TRENDS IN NANOSTRUCTURED MATERIALS 
Chairs: Joseph A. Akkara and John T. Prater 
Wednesday Afternoon, December 3, 1997 
America North (W)

1:30 PM *FF7.1 
IMPACT OF SURFACE CHEMISTRY ON THE PROCESSING AND SUPERPLASTIC PROPERTIES OF NANOCRYSTALLINE OXIDE CERAMICS. M.J. Mayo, The Pennsylvania State University, Dept. of Materials Science & Eng., University Park, PA.

Because of their large surface area, nanocrystalline powders often act as getters for chemical species present in the immediate environment. In our laboratory, we believe these adsorbed surface species have dramatically affected at least two material properties: 1) state of agglomeration during processing, and 2) superplastic behavior of the finished article. Agglomeration is the root cause of poor handling and sintering behavior for many ceramic powders; a review of current research shows that the culprit in many cases is the formation of surface chemical species which alter the solubility of the particle itself, thereby making possible the formation of interparticle necks by dissolution and reprecipitation. As a result, several standard practices in dealing with nanocrystalline oxide powders are contraindicated (e.g., storage under ambient conditions, aqueous milling of the powders, use of electrostatic stabilization for the manufacture of dispersions). If the adsorbed species contains an inorganic element, there can also be complications with respect to the superplastic properties. It will be shown that even submonolayer levels of a transition metal can affect superplastic strain rates by two orders of magnitude, while the incorporation of Si or other glass formers can notably change superplastic stress exponents.

2:00 PM FF7.2 
NOVEL PROCESSING ROUTES TO CONTROL GRAIN GROWTH IN SUBMICRON AND NANOPHASE ALUMINA COMPACTS. Deborah Vernon, Saryn Goldberg, and Janet Rankin, Brown University, Division of Engineering, Providence, RI.

In order to retain the material properties of nanosized powders in a fully dense compact grain growth during sintering must be minimized. We have developed and implemented two novel processing routes for preserving grain size in nanophase and submicron alumina compacts. Our processing routes involve an intermediary step between pressing and sintering. During this step the porous compact is chemically altered by either chemical vapor infiltration of silicon nitride or by liquid infiltration of zirconium propoxide. The infiltrated porous pellet is subsequently heated to 1650C for four hours. Density measurements show that the sintered pellet is 97 to 99% dense (final density). In this study we have examined the effects of using different initial pellet densities (ranging from 40 to 60% dense), and varying infiltrant concentrations. Our results show that the addition of either infiltrant reduces grain growth significantly. Grain growth and depth of infiltration were measured using transmission electron microscopy (TEM) and scanning electron microscopy (SEM). High resolution electron microscopy (HREM) and electron energy loss spectroscopy (EELS) were used to study the grain boundaries in the infiltrated pellets.

2:15 PM FF7.3 
DIRECT OBSERVATIONS OF THE SINTERING OF SILVER AND COPPER NANOPARTICLES ON SINGLE CRYSTAL SUBSTRATES BY IN-SITU UHV TEM. Mark Yeadon, Judith C. Yang, Robert S. Averback, Jeffrey W. Bullard, J. Murray Gibson, Materials Research Laboratory, University of Illinois at Urbana-Champaign, Urbana, IL.

Using a novel UHV TEM with in-situ UHV sputtering attachment we have studied the sintering of copper and silver nanoparticles with single crystal substrates of both copper and silver. In the case of copper and silver particles on (001) copper, and silver particles on (001) silver, the particles initially assume random orientations. Upon annealing, however, the particles reorient and assume an epitaxial orientation with the substrate. In the case of silver on silver, and copper on copper, homoepitaxy occurs by a process involving sintering and grain growth. In the case of silver on copper, grain growth cannot occur since the metals are immiscible. The surface energy of the deposit is also lower than that of the substrate and we observe the particles to wet the substrate surface and form a thin film with the epitaxial orientation relationship (111)Ag // (001)Cu, [110]Ag // [110]Cu.

2:30 PM FF7.4 
THE EFFECT OF TRACE OXIDES ON STRUCTURE AND PROPERTIES OF NANOPHASE METALS. Werner Wagner, Vincent Bonny, Jörg F. Löffler, Helena Van Swygenhoven, Paul Scherrer Institute, Villigen, SWITZERLAND; Danny Segers, University Gent, Gent, BELGIUM.

Metal clusters, when produced by inert-gas condensation, can absorb oxygen from the residual gas atmosphere of the recipient. Therefore, after consolidation, these materials are often contaminated with trace oxides. For example, transition metals like Fe, Ni and Co after consolidation were found to form a structure of metal clusters embedded in interfacial phases of oxides, which influenced markedly the magnetic properties. Likewise, the analysis of the combined structural and magnetic properties allowed a characterization of the oxide structure including structural changes upon annealing. Besides the transition metals we investigated also the influence of trace oxides on the synthesis properties of nanophase Pd. This noble metal is found to undergo grain growth during consolidation, which can be stabilized by intentional addition of oxygen. Combining different techniques, i.e. density measurements, x-ray diffraction, small angle neutron scattering and positron annihilation, the main structural parameters like grain size, porosity and free volume distribution are investigated and related to the content and structure of oxides.

3:15 PM FF7.5 
MICROSTRUCTURE AND PROPERTIES OF OXIDE CERAMIC-BASED NANOCOMPOSITES WITH TRANSITION METAL NANOPARTICLES. Tohru Sekino, Shunichi Etoh, Yong-Ho Choa and Koichi Niihara, Inst of Scientific and Industrial Research, Osaka Univ, Osaka, JAPAN.

Transition metal nanoparticles dispersed oxide ceramic nanocomposites (Al2O_3/Co and ZrO_2/Ni, in wich metal content is less than 20 vol%) have been fabricated by the reduction and sintering of composite powders. These powder mixtures were prepared by solution chemical processes to obtain suitable structure for ceramic/metal nanocomposites. Nickel nitrate or cobalt nitrate, as a source of metal dispersion, was dissolved into alcohol and mixed with alumina or zirconia powders. High temperature XRD analysis revealed that nitrates were decomposed to corresponding metal oxides above 400^C in air. Calcined mixtures exhibited that metal oxide nanoparticles were precipitated homogeneously on the ceramic particles. These powders were reduced by hydrogen and successively hot press sintered at 1400 to 1600^C with an applied pressure of 30 MPa. Nanometer-sized Co or Ni particles were mainly dispersed at the matrix grainboundaries. High resolutional TEM observation revealed that heterogeneous interfaces between metal and oxide ceramics were basically clean without any reaction phase. Mechanical properties such as fracture strength of these composites were improved by dispersing nano-sized metal particles due to microstructural refinement although the softness of dispersed metals. Ferromagnetic responses were observed by magnetization measurements for these composites. Relationships between microstructure, mechanical and brief magnetic properties for these ceramic/metal nanocomposites will be discussed.

3:30 PM *FF7.6 
PARTICLE ADHESION: INTERACTION FORCES AND MECHANICAL EFFECTS. D.S. Rimai, L.P. DeMejo, B. Gady, D.J. Quesnel, Eastman Kodak Company, Rochester, NY; R.C. Bowen, Johnson and Johnson Company, Rochester, NY; R. Reifenberger, Purdue University, West Lafeyette, IN.

The adhesion of particles to substrates is a complex problem which depends on a combination of the interaction forces and the mechanical properties of the materials. Indeed, due to the adhesion-generated stresses, either elastic or plastic deformations of the contacting materials can occur. In addition viscoelastic creep can also occur for particles having radii less than some critical radius determined by the requirement that the particle radius equal the contact radius. When the critical radius is reached, the particle can actually become totally engulfed by the substrate, thereby disappearing from the surface of that substrate. This paper will discuss the nature of particle-substrate adhesion. SEM micrographs and AFM forces measurements illustrating elastic, plastic, and viscoelastic effects will be shown. In addition the contributions of the electrostatic and van der Waals interactions to particle adhesion will be discussed.