Abstract
Self-assembled epitaxial NiSi2 nanowires have been fabricated on (001)Si by reactive deposition epitaxy (RDE). The RDE method promoted nanowire growth since it provides deposited atoms sufficient kinetic energy for movement on the Si surface during the growth of silicide islands. The twin-related interface between NiSi2 and Si is directly related to the nanowire formation since it breaks the symmetry of the surface and leads to the asymmetric growth. The temperature of RDE was found to greatly influence the formation of nanowires. By RDE at 750 °C, a high density of NiSi2 nanowires was formed with an average aspect ratio of 30. Self-assembled NiSi2 nanowires with a high-aspect ratio have been fabricated by combining the methods of RDE and nitride-mediated epitaxy (NME). Both types of epitaxial NiSi2 nanowires, which are parallel and twin related to the substrates, were formed with the length/width aspect ratios increased by a factor of 8 with the effect of NME. One type of nanowire was successfully grown with a high-aspect ratio despite the four-fold symmetric epitaxial relationship between NiSi2 and Si with very small mismatch. The use of NME method effectively diminished the flux of Ni atoms and allowed sufficient time for the strain to be released by means of shape transition during the island growth at elevated temperatures. Endotaxial growth of self-assembled α-FeSi2 nanowires on (100)Si has been achieved by combining RDE and NME. The length and the length/width aspect ratio of metallic α-FeSi2 nanowires could be increased more than 12 and 6 folds to 2 μm, and 200 respectively, with a narrow width of 5-10 nm after prolonged annealing. The adjustment capability is attributed to the diminished flux of Fe adatoms mediated by the Si3N4 barrier layer to allow more complete shape transition. The scheme represents a degree of control on the morphology of self-assembled epitaxial silicide NWs not achievable otherwise. Au-Ni alloy have been used as metal source of RDE to enhance the growth of self-assembled silicide nanowires. The rate of adatom rearrangement can be increased significantly by the formation of a fast diffusing path at the silicide/Si interface as a result of the low Au-Si eutectic point. The result demonstrated an essential role of the rearrangement of atoms in the process of formation of epitaxial silicide NWs.