Electronic properties of Cu clusters and islands and their reaction with O2 on SnO2(110) surfaces

Abstract

The deposition of Cu on SnO2(110) surfaces, and its oxidation to CuxO, have been studied by low-energy electron diffraction (LEED) and angle-integrated photoemission using synchrotron radiation photoemission spectroscopy (SRPES). With the growth of copper on SnO2(110), which was found to follow the Volmer-Weber (“islanding”) growth mode, a small amount of metal-phase Sn segregates to the surface, and even when the copper thickness reaches several tens of A, Sn metal still is seen at the surface. But when this surface is annealed at 800 K in 5 × 10−6 mbar O2 for 20 min, the Sn atoms are totally converted to SnO2. Simultaneously, the deposited Cu atoms become oxidized. The surface charges up both during LEED and SRPES data acquisition. The clean SnO2(110) surface shows a 1 × 1 structure. With Cu deposition, the substrate LEED pattern gradually becomes weaker. With even more copper deposited, a Cu(111)-1 × 1-oriented particle structure appears, indicating coalescence of the Cu islands to 3-dimensional Cu(111) epitaxy. After subsequent heating to 500 K, the substrate signal appears again, and we see the SnO2 1 × 1 pattern. In conclusion, Cu atoms quite easily form clusters on the SnO2(110) surface already after a slight heat treatment. The results show that this system is quite active towards O2 gas exposure, and that the surface conductivity changes during O2 exposure.