Electron beam induced formation of tungsten sub-oxide nanorods from flame-formed fragments

The rapid formation of tungsten oxide nanorods through electron beam (EB) irradiation on the surface of micron-sized flame formed tungsten-oxide fragments is reported. The micro-sized fragments (precursor material) were formed in a counter-flow methane diffusion flame on the surface of a tungsten wire. Nanorods of various lengths and aspect ratios were rapidly formed in the surrounding area of a transmission electron microscope copper grid as the micro-sized fragments were exposed to a concentrated electron beam. The EB was produced using a 200 keV transmission electron microscope. The length of the formed nanorods is inversely proportional to the distance of the precursor material. We show that the most significant growth or conversion of nanorods from a flame formed fragment occurs within the first second of the EB irradiation; principally owing to the considerable amount of residual stresses attained in the material as they are formed in a high flame temperature environment. It was found that the produced nanorods are composed of a lower oxygen state of tungsten oxide than the precursor material. A growth mechanism is proposed and discussed.