LIMITATION OF AUGER-ELECTRON SPECTROSCOPY IN THE DETERMINATION OF THEMETAL-ON-OXIDE GROWTH MODE - PD ON MGO(100)

A discussion on the use of Auger electron spectroscopy as a quantitati ve tool to determine the growth mode of metals on single crystal oxide surfaces is presented. In the case of Pd grown epitaxially on MgO(100 ), the three-dimensional character of the growth is easily seen at cov erage above one monolayer. However, in the submonolayer regime, and ma inly at low substrate temperatures, the AES results are ambiguous. The combination of AES with the more sensitive helium-atom diffraction me thod allows us to demonstrate that the growth is three-dimensional fro m the early stages, the particles becoming flatter when the substrate temperature decreases. We compare our results with other growth studie s on different metal/oxide systems. At low temperature, the ideal grow th modes are not always observed, the final morphology of the films be ing determined mainly by kinetic effects. Thus a pseudo-Stranski-Krast anov growth mode is often obtained with formation of 2D islands follow ed by 3D clustering from a critical submonolayer coverage.