Growth of single crystal tungsten nanorods by oblique angle sputter deposition

We report the creation of single crystal tungsten nanorods with unusual simple cubic phase. These novel nano-structures were grown by oblique angle sputter deposition with substrate rotation through a shadowing effect. Transmission electron microscopy (TEM) diffraction patterns from individual nanorods clearly show the single crystal structure. It is evident from TEM diffraction measurements, during the oblique angle deposition, both beta-phase W(100) and alpha-phase W(110) islands exist at the initial stages of growth. However, at later stages of the growth the beta-phase structure dominates. This is in contrast to the sputter deposition at normal incidence where only the thermodynamically stable bee a-phase W(110) polycrystalline films were formed when the film grew to a certain thickness. We explain our results by using the shadowing and adatom mobility mechanisms: At the initial stages of growth, the beta-phase W(100) islands grow taller due to the lower adatom mobility on these islands. The taller beta-phase W(100) islands survive in the competition during oblique angle growth and form isolated nanorods in the later stages, while the shorter alpha-phase W(110) islands stop growing due to the shadowing effect. In addition, our Monte Carlo simulation results agree well with the experimental measurements.