Abstract
The growth of epitaxial Si nanowires by a metal-catalyst-free process has been investigated as an alternative to the more common metal-catalyzed vapor–liquid–solid process. The well-aligned Si nanowires are successfully grown on a (111)-oriented Si substrate without any metal catalysts by a thermal treatment using silicon sulfide as a Si source at approximately 1200 °C. The needle-shaped Si nanowires, which have a core–shell structure that consists of a single-crystalline Si core along the <111> direction consistent with the substrate direction and a surface coating of silicon oxide, are grown by a metal-catalyst-free process. In this process, the silicon sulfide in the liquid phase facilitates the nucleation and nanowire growth. In contrast, oxygen-rich nanowires that consist of crystalline Si at the tip and lumpy silicon oxide on the body are observed in a sample grown at 1300 °C, which disturbs the epitaxial growth of Si nanowires.
Highlights
A simple thermal treatment, which is described in the Methods section, enables the epitaxial growth of well-aligned nanowires on a Si substrate by a metal-catalyst-free process
In the method using sulfur and catalytic Au, nanowires are grown at 1230 °C, and the source gas in this growth is vapor-phase Si sulfides, which are produced by etching the Si substrate at a higher temperature than the sublimation point of SiS (940 °C) and the boiling point of SiS237
The growth of oxygen-rich nanowires is dominant at higher temperatures
Summary
Been several reports on Si nanowires synthesized by laser ablation using mixtures of Si and silicon oxide as the source[27,28,29,30] These methods do not require any metal catalysts, the product is an aggregate of bent nanowires. The epitaxial growth of well-aligned Si nanowires on a Si substrate by a metal-catalyst-free process has not been achieved yet. We report the growth of epitaxial Si nanowires on a Si substrate by a metal-catalyst-free process. The nanowires grown by the metal-catalyst-free process are single-crystalline Si along the direction and the surface is coated with silicon oxide. The determination of sulfur distribution and the management of sulfur contamination in the nanowire are issues to be addressed in the future
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