Silicon nanowhiskers in the diameter range of 70 to 200 nm were grown on 〈111〉-oriented silicon substrates by molecular-beam epitaxy. Assuming the so-called “vapor–liquid–solid” (VLS) growth process to operate, we initiated the growth by using small clusters of gold at the silicon interface as seeds. The in situ generation of the Au clusters as well as the growth parameters of the whiskers are discussed. The experimentally observed radius dependence of the growth velocity of the nanowhiskers is opposite to what is known for VLS growth based on chemical vapor deposition and can be explained by an ad-atom diffusion on the surface of the whiskers.

Spontaneous formation of ZnO dendritic nanowires has been achieved on the faceted surfaces of polyhedral Zn microcrystals by oxidizing the latter at 600°C. Electron microscopy investigations reveal that all the dendritic branches are elongated in ͗11-20͘ directions within the ±͑0001͒ primary planes, forming two-dimensional web-like structure. Homoepitaxial interconnections are observed at the branch-to-arm and branch-to-branch regions, and the whole dendrites are wurtzite single crystals. The growth process of the dendritic nanowires is discussed, which is proposed to be a combination of "self-catalytic liquid-solid" and vapor-solid process.

Silicon nanowires have received increasing attention as potential building blocks for nanoscale devices. We report the growth and analysis of silicon nanowires consisting of a crystalline silicon core and a thick oxide shell, which were grown by evaporation of silicon monoxide ͑SiO͒ in an inert gas atmosphere using a gold-coated silicon wafer as a substrate. This method combines SiO evaporation with the vapor-liquid-solid ͑VLS͒ nanowire growth mechanism. The resulting nanowires were analyzed using scanning electron microscopy, transmission electron microscopy ͑TEM͒, and energy-dispersive X-ray spectroscopy ͑EDXS͒. The thick oxide shell was determined to be the product of the SiO evaporation and subsequent phase separation into Si and SiO 2. The EDXS measurements confirmed the silicon core/oxide shell structure of the nanowires and the existence of a gold dot on the nanowire tip as required by the VLS mechanism. An explanation is proposed for growth of the nanowires by combination of the VLS mechanism and SiO disproportionation. High-resolution TEM micrographs show the crystalline structure of the nanowire silicon core. Some of the nanowires were found to show an oscillation in diameter.

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The development of simple gas sensing concepts is still of great interest for science and technology. The demands on an ideal device would be a single-step fabrication method providing a device which is sensitive, analyte-selective, quantitative, and reversible without special operating/reformation conditions such as high temperatures or special environments. In this study we demonstrate a new gas sensing concept based on a nanosized PtC metal-matrix system fabricated in a single step via focused electron beam induced deposition (FEBID). The sensors react selectively on polar H2O molecules quantitatively and reversibly without any special reformation conditions after detection events, whereas non-polar species (O2, CO2, N2) produce no response. The key elements are isolated Pt nanograins (2-3 nm) which are embedded in a dielectric carbon matrix. The electrical transport in such materials is based on tunneling effects in the correlated variable range hopping regime, where the dielectric carbon matrix screens the electric field between the particles, which governs the final conductivity. The specific change of these dielectric properties by the physisorption of polar gas molecules (H2O) can change the tunneling probability and thus the overall conductivity, allowing their application as a simple and straightforward sensing concept.