Si 4-5 nm wires grown from solution

from the tinier-and-tinier-hammers-and-chisels dept.
Jeffrey Soreff points out an article in Science [registration required] describing silicon crystals grown with "nearly uniform" diameters of 4-5 nm. The feat was performed using diphenylsilane in supercritical hexane at 500° C and 270 atmospheres. Click below for Jeffrey's summary of the article. Writing in [Science 287:1471-1473 25Feb2000] J.D. Holmes, K.P. Johnston, R.C. Doty, and B.A. Kogel describe growing silicon crystals with "nearly uniform" diameters of 4-5 nm is supercritical hexane. The temperature was 500° C and pressure was 270 bar. The silicon source was diphenylsilane. They used gold particles as seeds. "The nanowire synthesis relies on dodecane-capped Au nanocrystals, ranging between 20 and 30 Å in diameter, formed using standard arrested precipitation procedures to direct wire formation." In the absence of the gold, they get micron-scale Si agglomerated crud. The gold particles act as a sort of solvent for the Si, allowing controlled precipitation at the particle boundary to form a wire. It seems a bit strange that the wire diameter had a smaller dispersion than the Au dot diameter. They also ran experiments at different pressures (200 bar & 270 bar) and got different orientations for the wires (<100> vs. <110>). The authors were mostly interested in photoluminescence (which they measured) and in conductivity (which they speculated about). Could we use these wires as components? At the moment they certainly aren't atomically precise. I wish the authors had tried using the well-defined Au₅₅ clusters as seeds. Perhaps they did and something doesn't work with them… The authors did say that they saw thickness variations of only +-1 lattice spacing in their wires, though that seems to be within the individual wires, since their overall range spans more like 4 lattice spacings (3.14 Å Si(111) lattice spacing).