Physical vapor deposition and thermally induced faceting of tungsten nanoparticles

Nanoscale tungsten particles have attracted an increasing level of interest recently. In the current study, tungsten nanoparticles were fabricated utilizing physical vapor deposition and deposited on sapphire (α-Al₂O₃) substrates. The particles generated using this procedure were found to form a network with a continuous nanoporous structure. To study the influence of temperature and pressure on the stability and morphology of tungsten nanoparticles, a multitude of varying pre-heating steps were applied to these nanoscale tungsten particles in a vacuum chamber. The morphology and structure of the annealed tungsten particles were investigated by a series of materials characterization techniques including scanning electron microscopy, X-ray energy dispersive spectroscopy and X-ray photoelectron spectroscopy. The tungsten nanoparticles grew into nonuniform islands when annealed directly at 1100 °C, under a pressure of 10⁻⁷ Torr. Conversely, the deposited tungsten network transformed into individual, highly faceted nanoparticles when first pre-heated at an intermediate temperature, followed by annealing at 1100 °C, under a pressure of 10⁻⁷ Torr. Wulff analysis indicated that these well-developed tungsten particles exhibit {110} crystallographic facets.