Aggregation and sticking probability of gold on tungsten trioxide films

Both scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images show that gold layers, 0.8–3.2 nm thick, deposited on WO3 films aggregate into particles at temperatures above 400°C. The particles increase in size while the number density decreases over time. Particle size distributions indicate that the growth mechanism is coalescence due to island mobility rather than Ostwald ripening. Both SEM and X-ray photoemission spectroscopy (XPS) analysis indicate that the amount of gold deposited on the surface is approximately 50% of the value as determined by the quartz crystal monitor (QCM) during deposition. This difference is believed to be due to a low initial sticking probability of gold on the WO3 surface during deposition. Finding means to create and stabilize metal particles of the optimum size remains a problem in the fields of catalysis and gas sensors.