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.

Because of their importance in fundamental research and possible applications in nanotechnology and nanoelectronics, semiconductor nanowires have attracted much interest. In addition to the growth itself, the control of the size and location is an essential problem. Here we show the growth of ordered arrays of vertically aligned silicon nanowires by molecular beam epitaxy using prepatterned arrays of gold droplets on Si(111) substrates. The ordered arrays of gold particles were produced by nanosphere lithography.

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Single undoped Si nanowires were electrically characterized. The nanowires were grown by molecular-beam epitaxy on n+ silicon substrates and were contacted by platinum/iridium tips. I-V curves were measured and electron beam induced current investigations were performed on single nanowires. It was found that the nanowires have an apparent resistivity of 0.85Ωcm, which is much smaller than expected for undoped Si nanowires. The conductance is explained by hopping conductivity at the Si–SiO2 interface of the nanowire surface.

Silicon nanowires can be successfully grown by applying the vapor -liquid -solid process. In the case of the commonly used chemical vapor deposition technique, a Si containing gas/precursor is cracked at Au droplets acting as seeds. Si adatoms are subsequently dissolved in the liquid metal. Due to a supersaturation within this droplet, Si precipitates predominantly at the liquid -solid interface -a nanowire grows. A different situation occurs if nanowires are grown by molecular beam epitaxy via the vaporliquid -solid mechanism. The difference consists, for example, of the role of the metal seed, the morphology of the nanowires and their aspect ratio. In particular, surface diffusion including the metal used as well as Si, strongly influences the growth process. This article describes molecular beam epitaxy growth experiments of Si nanowires under ultra-high vacuum conditions and compares the results with other growth techniques.

Silicon nanowires can be successfully grown by applying the vapor – liquid – solid process. In the case of the commonly used chemical vapor deposition technique, a Si containing gas/precursor is cracked at Au droplets acting as seeds. Si adatoms are subsequently dissolved in the liquid metal. Due to a supersaturation within this droplet, Si precipitates predominantly at the liquid – solid interface – a nanowire grows. A different situation occurs if nanowires are grown by molecular beam epitaxy via the vapor– liquid – solid mechanism. The difference consists, for example, of the role of the metal seed, the morphology of the nanowires and their aspect ratio. In particular, surface diffusion including the metal used as well as Si, strongly influences the growth process. This article describes molecular beam epitaxy growth experiments of Si nanowires under ultra-high vacuum conditions and compares the results with other growth techniques.

Silicon nanowires are frequently grown involving a liquid gold droplet at their tips. Here we show that under certain circumstances the thermal oxidation of a silicon nanowire is drastically enhanced by the presence of this gold droplet. Such a gold-enhanced oxidation was observed in a temperature range from 1000 °C down to 250 °C. As a consequence, instead of the slow radial oxidation expected and desired for thinning the nanowires, a fast axial oxidation may occur catalyzed by the gold tip. This leads to a shrinking of the length of the Si nanowire and its replacement by a longer nanowire consisting of silicon dioxide. During this gold-enhanced oxidation process the gold droplet migrates from the tip to the base of the nanowire. Our experiments demonstrate that gold droplets lead to an enhanced dissolution of silicon during oxidation in the case that these remain in intimate contact with the Si nanowires.

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