Direct growth of germanium and silicon nanowires on metal films

We describe the basic thermodynamic and kinetic aspects that govern the growth of Si and Ge nanowires directly on bulk metal films. We illustrate essential differences between the vapour–solid–solid and the conventional vapour–liquid–solid nanowire growth. Ge and Si nanowires were formed on a select set of metal films including Ag, Al, Au, Cr, Cu and Ni. Metals that form silicides or germanides (Cr, Cu, and Ni) generally yield higher quality nanowires compared to nanowires grown on metal films whose equilibrium phases are defined by alloyed phases below eutectic temperatures (Al, Ag, Au). Combinatorial experiments presented here provide new basic insights into nanowire formation in the context of metal germanide and silicide formation rates. The mechanism established from our experiments successfully predicts the nanowire growth under a broad range of conditions and also predicts the nanowire growth on other metals to provide guidance to future progress in nanowire synthesis.