Silicon nanowire-based solar cells on metal foil are described. The key benefits of such devices are discussed, followed by optical reflectance, current-voltage, and external quantum efficiency data for a cell design employing a thin amorphous silicon layer deposited on the nanowire array to form the p-n junction. A promising current density of ∼1.6mA∕cm2 for 1.8cm2 cells was obtained, and a broad external quantum efficiency was measured with a maximum value of ∼12% at 690nm. The optical reflectance of the silicon nanowire solar cells is reduced by one to two orders of magnitude compared to planar cells.

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This paper reports a straightforward approach in generating spheroid-like particles and also the orientational orders observed in the self-assembly of these particles. Nonspherical particles, such as spheroid-like particles, are useful in both fundamental studies and industrial applications due to the geometry impact that they bring to the bulk properties of various material systems. Developing processes to generate nonspherical particles is an ongoing quest to meet the need of using such particles in different applications. The approach reported here takes advantage of a controlled chemical etching process. Exposing the spherical silica particles partially to carbon tetrafluoride in a reactive ion plasma-etching chamber transformed the particles from spherical shape into spheroid-like shape. A simple model is proposed to predict the geometry of the resulting nonspherical particles. The shape and dimension of the nonspherical particles generated through such a process matched well with the prediction of the model. The assembly of these spheroid-like particles showed a unique orientational order associated with the alignment of their axes. This approach will help further studies on the fundamental properties of the nonspherical particles, such as packing, rheology, and optical interaction.

We report the growth and characterization of bulk GaN single crystals by temperature-gradient recrystallization at high pressure and high temperature (HPHT), using apparatus adapted from that used to synthesize gem-grade diamond crystals. The bulk crystals are grown on seeds that were synthesized by hydride vapor phase epitaxy (HVPE) and subsequently removed from their sapphire substrate. Our largest crystals to date are 15×18 mm in diameter; however, the process is scalable to 50 mm and above. The crystals are transparent and well faceted, and dislocation densities below 100 cm−2 have been achieved. Additional characterization of the GaN crystals is also presented.

Transition-metal carbides in bulk form have historically been of technological interest primarily due to their excellent mechanical and refractory properties. As electronic materials these ceramic compounds are also particularly intriguing in that their electrical resistivity is relatively low compared to other ceramics and shows metallic temperature-dependent behavior. Some compositions also have superconducting transitions temperatures above 10°K. However, the synthesis of such materials in the form of one-dimensional nanostructures, which may be of interest for various nanoelectronic applications, is relatively difficult due to their refractory nature (Tmelt⩾2000°C). Here we report the synthesis of well-defined Mo2C nanowires and ribbons using a two-step approach in which we catalytically grow metal oxide nanostructures followed by in situ carburization. The growth mechanisms, microstructure, and initial electrical property measurements are discussed.

We report on the selective area heteroepitaxy and facet evolution of AlGaN nanostructures on GaN/sapphire substrate using various mask materials. We also report on the challenges associated with selection of an appropriate mask material for selective area heteroepitaxy of AlGaN with varying Al composition. The shape and the growth rate of the nanostructures are observed to be greatly affected by the mask material. The evolution of the AlGaN nanostructures and Al incorporation were studied exhaustively as a function of growth parameters including temperature, pressure, NH 3 flow, total alkyl flow, and TMAl/(TMAl+TMGa) ratio. The growth rate of nanostructures was reduced drastically when higher Al percentage AlGaN nanostructures were grown. The growth rates were increased for higher Al percentage AlGaN using a surfactant, which resulted in a high-quality pyramidal structure. As indicated by high-resolution x-ray diffraction and cathodoluminescence spectroscopy, the composition of Al in the AlGaN nanostructure is significantly different from that of a thin film grown under the same growth conditions.

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