Growth of Single Crystal Tungsten Nanorods by Oblique Angle Sputter Deposition

Abstract

We report the creation of single crystal tungsten nanorods with unusual simple cubic β-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 β-phase W(100) and α-phase W(110) islands exist at the initial stages of growth. However, at later stages of the growth the β-phase structure dominates. This is in contrast to the sputter deposition at normal incidence where only the thermodynamically stable bcc α-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 β-phase W(100) islands grow taller due to the lower adatom mobility on these islands. The taller β-phase W(100) islands survive in the competition during oblique angle growth and form isolated nanorods in the later stages, while the shorter α-phase W(110) islands stop growing due to the shadowing effect. In addition, our Monte Carlo simulation results agree well with the experimental measurements.

Phase transformation of single crystal β-tungsten nanorods at elevated temperatures

“…1 (¨0.79%) is consistent with the lower compressive stress values expected for the nanorods structure [12]. The mechanism that leads to the formation of h-W nanorods during oblique angle deposition is believed to originate from a competitive growth that includes the shadowing effect and different vertical growth rates and adatom mobilities on a-and h-islands [9,10]. The nanorods were¨450 nm in average length and¨75 nm in average width as observed from SEM images (not shown here, see Ref.…”

“…These prior observations suggest that for a h-W film with larger grain sizes and less number of grain boundaries, the phase transformation from h to a is expected to occur at relatively higher temperatures. In this letter, we report that the novel h-W nanorods obtained by oblique angle sputter deposition technique [9,10] transform to the a-phase only after annealing temperature reaches¨950 -C, which is much higher than the previously reported values. We explain the retardation of phase transformation by the lack of the grain boundaries in our single crystal W nanorods that makes the oxygen removal difficult and requires higher annealing temperatures.…”

A Compact Nanostructure Enhanced Heat Sink With Flow in a Rectangular Channel

“…2a, the top of the vertical nanorods has a pyramidal shape with four facets, which indicates that an individual nanorod has a single crystal structure. This observation was confirmed by previous studies [12][13][14] which reported that individual metallic nanorods fabricated by GLAD are typically single crystal. Single crystal rods do not have any interior grain boundaries and have faceted sharp tips.…”

Submerged Jet Impingement Cooling of a Nanostructured Plate

“…2a, the top of the vertical nanorods has a pyramidal shape with four facets, which indicates that an individual nanorod has a single crystal structure. This observation was confirmed by previous studies [16][17][18] which reported that individual metallic nanorods fabricated by GLAD are typically single crystal. Single crystal rods do not have any interior grain boundaries and have faceted sharp tips.…”