Aggregation and sticking probability of gold on tungsten trioxide films

Both scanning electron microscopy (SEM) and transmission electron microscop y (TEM) images show that gold layers, 0.8-3.2 nm thick, deposited on WO3 fi lms aggregate into particles at temperatures above 400 degreesC. The partic les increase in size while the number density decreases over time. Particle size distributions indicate that the growth mechanism is coalescence due t o island mobility rather than Ostwald ripening. Both SEM and X-ray photoemi ssion spectroscopy (XPS) analysis indicate that the amount of gold deposite d on the surface is approximately 50% of the value as determined by the qua rtz crystal monitor (QCM) during deposition. This difference is believed to be due to a low initial sticking probability of gold on the WO3 surface du ring deposition. Finding means to create and stabilize metal particles of t he optimum size remains a problem in the fields of catalysis and gas sensor s. (C) 2001 Elsevier Science B.V. All rights reserved.