The use of activated low density microcellular carbon (LDMC) as a catalysis supporter for nanophase Pt or Pd particles has been successfully developed in this study. The good dispersion and interfacial properties of nanophase Pt or Pd particles on activated LDMC are formed by using an impregnation and sintering process. The interfacial structures are examined by TEM, HRTEM and an image analyst system. No preferred orientation of interfacial bonding has been found between nanophase Pt and activated LDMC. The activated LDMC supported Pt or Pd catalysts have the high reactivity which can complete hydrogenation and oxidation of CO gas at low temperatures (<453 K). The catalytic activity of CO hydrogenation is increased as the size of the nanophase Pt and Pd particles decreases.

A study of the microstructural differences between exfoliated and non-exfoliated MoS2-based materials is presented, relating them to differences in their catalytic activity. Both commercial (crystalline) MoS2 and molybdenum sulfide catalysts prepared by thiosalt decomposition are subjected to chemical exfoliation reported to separate MoS2 monolayers from the original structure. Electron microscopy results show that the chemical treatment yields non-typical MoS2 nanostructures. Average surface area is also modified by exfoliation. The thiophene HDS activity of commercial MoS2 increases after exfoliation, while it decreases after exfoliation in the case of MoS2 catalysts.

Nanocrystalline materials have been intensely investigated in the recent past due to the novel properties associated with size-quantized particles. We have developed a new method for high yield, solution phase synthesis of nanocrystalline III-V semiconductors which eliminates the use of substituted or unsubstituted Group V hydrides and Group III alkyls. Our approach consists of in situ syntheses of (Na/K)3E (E = P, As, Sb) in aromatic solvents and subsequent reactions of these pnictides with Group III halide solutions in coordinating solvents. The nanocrystalline III-V semiconductors GaP, GaAs, GaSb, InP, InAs and InSb are readily prepared in a wide range of particle sizes (4–36 nm) and in high yields. The resultant Ill-V materials have been characterized by XRD, EDXA, TEM and elemental analyses.

This study deals with the initial oxidation of some 3d metal clusters in gas phase. In the experiments neutral metal clusters in a supersonic beam are made to collide with one or a few oxygen molecules in a reaction cell. The reaction products are detected with photoionization and mass spectrometry. By comparing the abundance of unreacted and reacted clusters, absolute sticking probabilities (S) can be determined. Transition metals with open d shells, e.g. Ni, have high, almost constant S for O2 on clusters containing more than 20 atoms. The size evolution of S for Cu, on the other hand, shows repeated minima and maxima. Cluster sizes which have high ionization potentials (IPs) and closed electronic shells, according to the spherical jellium model, are the ones with the lowest S. The IPs of CunO2 clusters have also been investigated. Compared with the IPs of the pure Cu clusters, the IPs of the oxidized clusters are generally higher and the large drops at the shell openings are less distinct.

The adsorption of ethoxysilanes RSi(OEt)3 on the Fe and Al surfaces from the vapor phase, water and toluene solutions was studied by the piezoquartz nanobalance and ellypsometry. The values of the “landing sites” and the energy of the interaction for different silanes were calculated. The self-assembling silane monolayers with good adhesion to the Al surface (due to the covalent bonds Al–O–Si) was shown to format during adsorption from dilute water solution. The influence of silane monolayers on the H2O adsorption and wetting of the surface was studied. The silane layers have considerably hydrophobic effect and prevent the growth of hydroxide film on the Al. The synthesis of charged silane nanophases was carried out by the addition of the acid (sulfo-, imididiaoetate-) and the basic (amino-) groups into the epoxysilane molecule. The effect of the charge density and the surface potential on the ion adsorption at the interface metal/electrolyte was investigated.

Isolated, monodisperse α-Fe clusters between 1.4 and 15 nm in diameter were prepared inside inverse micelles using an oil-continuous, nonaqueous system. The magnetic properties of these clusters were studied in a SQUID magnetometer as a function of cluster size, temperature and applied magnetic field. The blocking temperature, coercive field and remanent moment of 12.5 nm Fe clusters in inverse micelles are significantly lower than those reported for clusters of similar α-Fe core size but with a surface oxide. The novel synthesis technique may yield metallic clusters with essentially intrinsic magnetic properties.

Nanocrystalline (n-) Cu and Pd, prepared by inert gas condensation (IGC) and in situ room temperature (RT) and elevated temperature (warm) compactions, have been studied by small angle neutron scattering (SANS). Previous work [1] on room temperature compacted and subsequently annealed n-Pd seemed to show that all the scattering could be accounted for by a distribution of pores. Analysis of more extensive SANS measurements, together with the results of prompt gamma activation analysis (PGAA), indicates that the SANS can be explained by the presence of pores and hydrogen. Warm compaction reduces the hydrogen impurity level, while increasing the bulk density and decreasing the pore size. This can lead to a dramatic hardness increase in these materials.

The multilayer organization of sulfonated polyaniline/polyallylamine (SPAN/PAH) films was investigated by neutron reflectivity. Films were prepared by sequential adsorption of polycations and polyanions from dilute solution. Scattering contrast was achieved by selective deuteration of blocks of bilayers at varying intervals along the films. The internal organization of the multilayer structure was found to decay significantly with increasing number of bilayer depositions. In addition, a high degree of roughness was determined at the free surfaces of the films. Together, these results suggest that both conformal and nonconformal roughness are present in the films, i.e., defects introduced during individual layer depositions are to some degree transferred to the surface of subsequently deposited layers.

A method has been developed for determining the bond energies between nanosized particles from the kinetics of the rearrangement of aerosol agglomerates. The method of calculation is based on the change in Gibbs' free energy during restructuring. For Ag and Cu agglomerates, bond energies between the nanosized particles are of the order of magnitude calculated from bulk Hamaker constants.

Nanograined materials, with grain sizes in the range of 1–20 nm, exhibit significant enhancement of grain boundary dependent properties such as yield strength, intergranular fracture toughness, grain boundary diffusivity, specific heat and thermal expansion coefficient. Measurements by indirect techniques suggest that the grain boundaries in nanophase materials are structurally different from the boundaries in their conventional polycrystal counterparts. Exploratory HRTEM observations, on the other hand, indicate that the grain boundary structure in nanophase materials is the same as that found in grain boundaries in conventional polycrystals. This paper reports an HRTEM investigation of the microstructure in electrodeposited nanocrystalline (nc) Ni1wt.%P alloy. These observations reveal the presence of about 8-10 vol. % porosity in the microstructure. There is also evidence for the presence of an amorphous phase at some grain boundaries and triple junctions. A comparison of grain boundary structures with boundaries in conventional materials suggests that grain boundaries in the nc Ni-P alloy are, for the most part, normal.

In order to understand from a fundamental view how nanoparticles form and grow, classical molecular dynamics simulations of cluster growth and energy accommodation processes have been conducted for clusters of silicon (< 1000 atoms), over a wide temperature range. Simulations involved solution of the classical equations of motion constrained with the three body Stillinger-Weber potential. The results show the large heat release and resulting cluster heating during a cluster-cluster collision event, and the corresponding time evolution of the internal energy to a more stable state. Dynamic effects associated with the temperature of the cluster and the impact parameter are also clearly evident. In particular, clusters show a large sensitivity to temperature in the rate of coalescence, particularly at low temperature. Calculated diffusion coefficients are significantly larger than surface diffusion constants stated in the literature. Phonon density of states spectra do not seem to show size effects.

We present a computer simulation study of thin crystalline multilayers constructed from two FCC solids with differing lattice constants and binding energies. Both materials are described by Lennard-Jones interatomic potentials and initially have the same orientation and coherent interfaces. We have studied systems in which interfaces are perpendicular to the common [100] and [111] directions, respectively. A novel technique for analyzing local atomic ordering, Common Neighbor Analysis, is used to identify structural characteristics in these systems. We have found several structural changes in the layers of smaller atoms, including an FCC to HCP transition. In a system with (111) texture, a coherent interface to incoherent interface transformation is observed. Calculations of elastic constants of these multilayer structures show that elastic anomalies are associated with the structural variations.

We briefly describe a model which seems to be applicable to a variety of coalescence growth systems. Spanning cluster growth, particle growth and hillock formation in thin metal films, this model is based on the Smoluchowski kinetic equations and fractals. We describe how this model has been able to suggest the effect of translational to internal energy conversion in coalescing systems in determining the shape of particle size distributions. We also suggest how this model can be employed to account for the behavior of hillocks in supersaturated alloy films under thermal annealing conditions.

A modification of the conventional inert gas condensation apparatus for making nanostructured powders, wherein as evaporative source is replaced by a chemical source, is described. The new chemical synthetic process, called chemical vapor condensation(CVC), combines rapid thermal decomposition and expansion of a precursor/carrier gas stream in a hot tubular reactor with rapid condensation of the product particle species on a cold substrate under a reduced inert gas pressure of 1-50 mbar. The process has been used to synthesize loosely agglomerated nanoparticles (6 to 10 nm) of n-SiCxNy, starting from hexamethyldisilazane (HMDS) as precursor compound. The phase, morphology, and composition of n-SiCxNy powders can be modified by heat treatment. β-SiC particles with grain size less than 10 nm form after annealing at 1300°C in flowing Ar. In a 1:1 NH3/H2 mixture n-SiCxNy powders transform into α-Si3N4 whiskers, with [100] growth direction.

Nanoscale metal oxide particles have been synthesized by using a novel method which combines laser vaporization of metal targets with controlled condensation in a diffusion cloud chamber. The following oxides have been synthesized: ZnO, SiO2, Fe2O3, Bi2O3, PdO, NiO, AgO, TeO, Sb2O3, TiO2, ZrO2, A12O3, CuO, In203, SnO2, V2O5 and MgO. With this method, the size of the particles can be conveniently controlled by careful control of the degree of supersaturation which is accomplished by adjusting the temperature gradient, total pressure, and partial pressure of the metal vapor generated by laser vaporization in a diffusion cloud chamber. The microscale structures of the SiO2 and A1203 particles exhibit interesting web-like matrices with a significant volume of vacancies. These materials may have special applications in catalysis and as reinforcing agents for liquid polymers.

Nanocomposites of copper with low concentrations of dispersed fullerenes were synthesized by simultaneous sputtering of copper and sublimation of fullerenes. Postdeposition heat treatments at 400 and 800 °C were performed to assess the thermal stability of the microstructure and the effect on the Vicker's microhardness. The as-deposited copperfullerene composite has submicron-scale granularity, in contrast to pure copper which has conventional columnar growth. Grain growth in the heat-treated fullerene-containing specimens is suppressed and the microhardness enhanced relative to pure copper.

The v(SiH) stretching absorption band is known to be sensitive to the local environment of the silicon atom. The presence of SiH groups on silicon carbide surface can be taken advantage of to evaluate the oxidation degree of this ceramic powder.

The surface analysis of a SiC nanosized powder was performed by FT-IR spectrometry. The evolution of the v(SiH) absorption band, followed in situ under controlled temperatures and oxygen pressures, consists in a frequency shift toward higher wavenumbers when oxidation proceeds. The resolution of the Sill absorption range into four subbands corresponding to the HSiOxC3−x possible surface groups showed the relative evolution of the different species. Ab initio SCF MO calculations on molecular models gave evidence of the charge transfer to the more electronegative oxygen atom, making the silicon atom more positive and seemingly strengthening the SiH bond and thus inducing an upward shift of the v(SiH) frequency.

The gas-condensation technique is used to produce the nanocrystalline WO3−C, Pt/WO3−X and Pd/WO3−X powders under different atmospheres and pressures. High resolution electron microscope shows there exists well bonded interface between Pt or Pd and WO3−X The WO3−X, Pt/WO3−X and Pd/WO3−x nanocrystals grow into needle shape with plate inside when these asevaporated powders are compacted and sintered at 900 °C for two hours. The plate grows preferentially in {220) plane along < 001 > direction. However, the mean particle size of nanophase Pt and Pd only increases from less than 10 nm to 30 nm and 50 nm, respectively. The gas chromatography results show that nanophase Pt/VO3−X powders have better catalytic effects in converting CO to CO2 than nanophase WO3−X and Pd/WO3−X powders.

As reported previously, perfect facets can be achieved at the side walls of submicron silicon mesa structures grown by molecular beam epitaxy (MBE) with micro shadow masks [1]. An essentially self organizing, three-dimensional growth was observed. In this paper we present the results of the epitaxial growth on (001) substrates using long (≥ 1μm), lineshaped mask apertures, which put constraints on the formation of facets. At a growth temperature of 500°C {111} facet formation is observed for lineshaped mesas oriented along the <110> direction of the substrate. Side walls with a length of I μm are perfectly plane, while mesas with a length of 10 μm and more show rough sidewalls. This is explained by a limited silicon adatom diffusion on the facet. For higher flux rates the facet formation is suppressed. This can be understood in terms of a reduced adatom diffusion.

A crossover from {111} to {113} facet formation is observed at growth temperatures above 500°C. A model for the temperature dependent formation of {111} and {113} facets is given.

The oxygen-containing silicon (Si) ultrafine particles have been deposited onto Si and SiO2 substrates by evaporation of Si powder in an oxygen-containing argon atmosphere. The asdeposited Si ultrafine particles exposed to the ultraviolet light emit blue light, which is strong enough to be seen with the naked eye. The blue light emission is associated with a broad photoluminescence (PL) peak at 2.7 eV, which is attributed to radiative recombination via a radiative recombination center. The proposed model with one radiative and two nonradiative recombination centers well explains the temperature-dependent PL peak intensity.