Temperature-controlled growth of silicon-based nanostructures by thermal evaporation of SiO powders

Silicon-based nanostructures with different morphologies, sizes, compositions, and microstructures were grown on Si wafers by thermal evaporation of SiO powders at 1350 degreesC for 5 h under 300 Torr of a flowing gas mixture of 5% H-2-Ar at a flow rate of 50 standard cubic centimeters per minute (sccm). The SiO powders and Si wafers were placed inside an alumina tube, which was heated by a tube furnace. The local temperature inside the tube was carefully calibrated by a thermal couple. After evaporation, Si-containing products with different colors and appearances were formed on the surfaces of the Si wafers over a wide temperature range of 890-1320 degreesC and a long distance of similar to 85 mm. Basing on the colors and appearances of the products, five distinct zones, which corresponding to different: temperature ranges, were clearly identified from the highest temperature of 1320 degreesC to the lowest temperature of 890 degreesC. They are zone I (1250-1320 degreesC), zone II (1230-1250 degreesC), zone III (1180-1230 degreesC), zone IV (930-1180 degreesC), and zone V (890-930 degreesC). The deposited products were systematically studied by scanning electron microscopy, transmission electron microscopy, and X-ray diffraction. The results show that, besides Si nanowires, many other kinds of Si-based nanostructures such as octopuslike, pinlike, tadpolelike, and chainlike structures were also formed. The temperature distribution inside the alumina tube was found to play a dominant role on the formation of these structures. It is demonstrated that a control over the growth temperature can precisely control the morphologies and intrinsic structures of the silicon-based nanomaterials. This is an important step toward design and control of nanostructures. The growth mechanisms of these products were briefly discussed.