Metal-catalyst growth of silicon nanowires in UHV and furnace systems

Silicon wires and nanowires were grown on Si(111) substrates at various pressures ranging from ultra high vacuum (∼10−8 Torr) to near atmospheric pressure of 500 Torr. Two separate deposition chambers were used in this study, including an ultra high vacuum (UHV) chamber and a high temperature, tube furnace based chamber for operation at the higher pressures of 10−3 Torr to atmospheric pressure. In the UHV chamber at a growth temperature of 800°C, silicon wires were observed growing perpendicular to the silicon substrate by using Pulsed Laser Deposition (PLD) of silicon. The growth scheme was based on vapor-liquid-solid mechanism using gold as the mediating catalyst. Various shaped silicon wires were found, with typical wire diameters of 200–700 nm. The maximum length of the grown wire was approximately 1.6 μm in height. Images of the silicon wires were taken with Scanning Electron Microscope (SEM).; In a separate chamber made for high temperature and higher pressure (near atmospheric) deposition, silicon nanowires were grown simply by annealing gold coated Si(111) substrates. Four different thicknesses of gold films including 5, 10, 18 and 112 nm-were used. The growth temperature was about 1100°C with pressures ranging from 1.6 × 10−1 Torr to 500 Torr. It was observed that a high density of silicon nanowires formed only when the thickness of the gold film was greater than about 18 nm. The effect of changing various factors such as further increases in the gold film thickness, annealing time, and the pressure did not significantly affect the density of nanowires or the distribution of diameters among the nanowires. The typical dimensions of the observed silicon nanowires had diameter of 20–160 nm and tens of μm in length. Some nanowires with diameter as small as 10 nm were found. Images of the silicon nanowires were taken with SEM and Transmission Electron Microscope (TEM). The Energy Dispersive X-Ray Spectroscopy (EDS) showed oxygen content in all the nanowires that were grown.