Lattice Constant and Crystallite Size of Condensed Gold Vapor

Abstract

Gold wires were vaporized by the exploding-wire phenomenon using a 20 μF capacitor bank charged to voltages up to 14 kV. The resulting condensate, an aerosol or metallic smoke, was collected on membrane filters and subjected to X-ray analysis to determine lattice constant, crystallite size, and behavior with isothermal annealing. Wire explosions were conducted in au ambient atmosphere of ait or nitrogen at barometric pressure. It is estimated that the quench rate for this material is of the order of 10⁸ deg/sec from the melting point although no substrate is involved and it is expected that any effects of epitaxial origin on the structure would be minimized.Before annealing, diffractograms showed broad peaks apparently shifted to the high-angle side. Line breadth may be attributed primarily to particle size broadening, since ft correlates well with size determined by electron microscopy, (β cos θ) is linear with θ, and [(β cos θ)/λ] is approximately constant for three radiations used. Crystallite size is of the order of 400 Å and is observed to decrease roughly with increasing voltage used for vaporization. The observed lattice decrement, approximately 0.2%, generally increases with voltage used for vaporization, and apparently correlates rather well with the inverse of sise as has been reported in some work on thin gold films. However, studies of colloidal gold particles do not show significant lattice shifts, although the particle size is less than 100 Å so that the decrements observed may be due to factors other than size alone. For this black, particulate material, some lattice decrement apparently persists even after protracted isothermal annealing below the melting point. Crystallite size increases with annealing but remains below about 1000 Å. Results suggest that the lattice decrements observed in condensed gold vapor are due to surface tension effects and the presence of vacancy aggregates.