Growth, electronic properties and reactivity of vanadium deposited onto a thin alumina film

The interaction of metals with oxide surfaces plays an important role in the manner of growth of the metal/oxide interface and eventually for the electronic properties and chemical reactivity of the resultant surface. We have investigated such effects for vanadium on alumina. By using a thin alumina film grown on a NiAl(110) as a model substrate, we were able to apply scanning tunneling microscopy (STM) as well as electron spectroscopic techniques without charging problems. According to our STM results, vanadium deposition at 300 K results in the formation of small thin particles/islands partly incorporated into the film at low coverages. With increasing coverage three-dimensional growth is found. The thermal stability and the growth behaviour of these nuclei at elevated deposition temperatures (greater than or equal to 600 K) are in agreement with a strong metal substrate interaction. In the coverage regime below 0.1 ML, X-ray photoelectron and X-ray absorption spectroscopy data provide evidence that the deposits are oxidized to Vx+, 1<x<2. Furthermore, we have studied the interaction at 720 K and in an ambient atmosphere of oxygen in order to check how vanadium reacts with the alumina film under more severe conditions. In fact, a thickening of the alumina film has been observed, which we ascribe to a catalytic effect of vanadia on the alumina film growth. (C) 1999 Elsevier Science B.V. All rights reserved.