Epitaxial growth of vertically free-standing ultra-thin silicon nanowires

We report epitaxial growth of ultra-thin vertically free-standing silicon nanowires (Si NWs) on Si(111) and Si(110) substrate, by an ultra-high vacuum chemical vapor deposition method. The epitaxial growth direction of Si NWs with sub-10 nm diameters was found to be dependent upon the orientation type of the Si substrate. The 〈112〉 and 〈110〉 epitaxial growth directions are crystallographically preferred on Si(111) and Si(110) substrates, respectively. Especially, for the epitaxy on Si(110), most of the Si NWs are grown vertically in the [110] direction with sub-5 nm diameters. Based on transmission electron microscope investigations, a growth model for ultra-thin Si NWs was deduced from the morphology of interface between catalyst and nanowire, and the growth direction at a very early stage of epitaxy was determined.