TaSi 2 nanowires have been synthesized by annealing FeSi2 thin film and nanodots grown on a Si substrate in an ambient containing Ta vapor. The TaSi2 nanowires are formed in three steps; segregation of Si atoms from the FeSi2 underlayer to form Si base, growth of TaSi2 nanodots on Si base, and elongation of TaSi2 nanowire along the growth direction. Strong field-emission properties promise future electronics and optoelectronics applications.
An electric-field mechanism has been developed to explain the oxide-assisted growth of silicon nanowires. This mechanism assumes a strong electric field at the tip of silicon nanowires. Most of the SiO molecules would be attracted by this electric field and then land on the nanowire tip. Thus, the silicon nanowire growth is restricted at the tip only. The maximum electric field that could possibly exist has been estimated from the field emission data. The probability of SiO vapor landing on the nanowire tip is calculated for a wide range of conditions. The result shows that for a sufficiently strong electric field, all SiO vapor would land on the nanowire tip. This attractive force to the nanowire tip is even more pronounced if the SiO vapor first condenses to form a larger cluster. All these calculation results suggest that this electric-field mechanism is possible.
The excess temperature at the tip of silicon nanowires during their growth is calculated and found to be generally low. Therefore the special adhesive property of the tip cannot be explained by the excess temperature. The effect of surface tension is analyzed and we found that it cannot cause a significant lowering of melting point at the tip. Based on the charge-assisted mechanism proposed earlier by us, we note that charge accumulation at the tip results in a strong negative pressure. We propose that this is the key force driving the nanowire to have only one-dimensional growth.
Self-assembled NiSi quantum-dot arrays have been grown on relaxed epitaxial Si0.7Ge0.3 on(001)Si. The formation of the one-dimensional ordered structure is attributed to the nucleation of NiSi nanodots on the surface undulations induced by step bunching on the surface of SiGe film owing to the miscut of the wafers from normal to the (001)Si direction. The two-dimensional pseudohexagonal structure was achieved under the influence of repulsive stress between nanodots. Since the periodicity of surface bunching can be tuned with appropriate vicinality and misfit, the undulated templates promise to facilitate the growth of ordered silicide quantum dots with selected periodicity and size.
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