Deposition of reactive and non-reactive metals on titanium dioxide - chromium and cobalt

摘要

The deposition of chromium and cobalt on TiO_2 substrates is analyzed in a comparative study using synchrotron based photoelectron spectroscopy methods. Upon deposition of chromium the electronic structure of the TiO_2 substrate is modified. The substrate is reduced while the deposited Cr becomes oxidized. Two states are observed to appear within the electronic gap and their distinct character of either Cr 3d or Ti 3d is revealed by Resonant Photoelectron Spectroscopy (ResPES). When a Cr thickness of 1.3 ML is reached, metallic Titanium is observed as well as metallic chromium. The properties of Cobalt deposited on TiO_2 differ from that behaviour. The reaction is only observed during the very first steps of the Co growth. Only some of the deposited Co is oxidized to Co~(2+) while metallic Co is the dominating component. From thermodynamic considerations a 2-dimensional growth mode for the reactive metal (chromium) is concluded while in contrast to this, Cobalt is considered to have a 3-dimensional cluster growth mode corresponding to its character as non-reactive metal.