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The composition, structure, light emission and oxidation kinetics of Si(1-x)Ge(x) alloy nanocrystals ( approximately 3 nm in diameter) synthesized by nonthermal plasma have been investigated. It is found that the synthesized nanocrystals are neither a mixture of Si nanocrystals and Ge nanocrystals nor Si-Ge (Ge-Si) core-shell nanocrystals. The H coverage at the surface of Si(1-x)Ge(x) nanocrystals decreases with the increase of the Ge atomic fraction. The incorporation of Ge enhances the oxidation of Si(1-x)Ge(x) nanocrystals when the atomic fraction of Ge is <0.5. No shift in photoluminescence from hydrosilylated Si(1-x)Ge(x) nanocrystals is observed when the atomic fraction of Ge varies between 0 and 0.1, indicating that the bandgap of Si nanocrystals is similar to that of Ge nanocrystals at a nanocrystal size of 3 nm.

We have investigated silicon particles formed in an inductively coupled plasma (ICP) system and have measured their structural properties by electron microscopy. ICP silane plasmas are shown to be an interesting and versatile source of nanoparticles. Three regimes are mapped out: a regime of no observable particle growth at the lowest pressures, a regime of polydisperse and agglomerated particles at the highest pressures, and a regime yielding highly monodisperse particles at intermediate pressures. Our results suggest that an ICP allows this unique production of monodisperse nanoparticles at high concentrations. The particle size can be controlled from 15 to 200 nm and is determined by the plasma on time. For short plasma times, particle growth appears to be due primarily to coagulation, while in the second phase particle growth is attributed primarily to surface deposition. For H[SUB2] dilutions less than 92%, the growth rate is almost independent of H[SUB2] partial pressure. Transmission electron micrographs, however, indicate that the addition of hydrogen decreases the particle density. At higher dilution ratios, polycrystalline particles are obtained. Under all other conditions the particles are amorphous. [ABSTRACT FROM AUTHOR]

Mixed phase, hydrogenated amorphous and nanocrystalline silicon thin films grown by co-deposition (nanocrystals and amorphous material deposited sequentially in the same vacuum system) demonstrate pronounced quantum confinement effects. Based on photoluminescence measurements of co-deposited samples, we find evidence that the optical gap of nanocrystals embedded in hydrogenated amorphous silicon is increased to energies exceeding bulk crystalline silicon values -- at least as high as 1.35 eV. The broad spectrum of emission of the nanocrystals is attributed to the size distribution and local fluctuations in matrix hydrogenation. The temperature dependence of this PL suggests that these nanocrystals possess fewer defects than those grown by conventional plasma enhanced chemical vapor deposition methods. Interactions between electronic states in nanocrystals and localized states in amorphous silicon matrix tissues are discussed in terms of their role in determining the strength of the quantum confinement potential. [ABSTRACT FROM AUTHOR]

Abstract: While silicon''s optical properties are improved at the nanoscale, they also become highly sensitive to the properties of the surfaces and interfaces of silicon nanostructures. For instance, while reported quantum yields for photoluminescence of silicon quantum dots covered by a native oxide are often in the few percent range, quantum yields as high as 30% have been found in quantum dots whose surfaces were passivated by covalently bonded organic molecules. In this paper, we describe an approach that is based on the gas phase synthesis of silicon quantum dots in a nonthermal plasma, and the subsequent organic surface passivation in the liquid phase. Nanocrystals are formed within a few milliseconds with a high mass yield in a nonthermal plasma. Various organic ligands such as octadecene, dodecence, and styrene are grafted onto the nanocrystal surfaces in a reaction known as hydrosilylation. Materials are characterized through transmission electron microscopy, atomic force microscopy, and fluorescence measurements. The particle size distributions are found to be relatively monodisperse and are well controllable through the plasma process parameters. Photoluminescence quantum yields as high as 60–70% have been achieved for particles luminescing in the red range of the visible spectrum. [Copyright &y& Elsevier]

Abstract: Nanoindentation-induced dislocation emission at 5–7nm displacements in ultra-thin films (12–33nm) and nanocubes (40–60nm) is used to examine deformation and plasticity models. Using the Tabor estimate, this displacement corresponds to a plastic strain of 3–5%. Load–displacement curves produced using nanoindentation show evidence of discretized, Burgers vector–length displacement steps, or excursions, which can be associated with individual dislocation emission events. Using these displacement steps and the residual plasticity present on unloading, theoretical hardening models are developed. Linear and parabolic hardening approaches are compared for ultra-thin films of nickel, cobalt, and Permalloy (Ni80Fe20), and also for silicon nanocubes. It is determined that the linear hardening model can predict the early trends of the experimental data while parabolic hardening may be more appropriate at later stages. [Copyright &y& Elsevier]