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Si nanowires produced using a Si(111) substrates which had a native oxide present prior to the growth.. The growth was performed at 1050 °C for 1 h using a 36 sccm Ar to gas ratio.
Si wafer annealed at 1100 °C in a vacuum, under gas flow. Note the extended cracks and the presence of silicon nanowires (white regions) only within these regions, while the smooth silicon areas contain no wires.
Model for the growth of Si nanowires: The layer experiences large tensile stress, while the underlying Si region undergoes biaxial compressive stress due to difference in thermal expansion. The tensile stress in the oxide layer leads to stress cracks, which relieve the stress locally. This stress gradient results in mass transport to and the accumulation of Si atoms at or near the cracks, where material starts to build up, initiating the growth of the nanowires. The addition of hydrogen allows much enhanced surface diffusion along the concentration gradient, leading to the growth of long nanowires with a large aspect ratio.
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