ELECTRONIC-PROPERTIES OF CU CLUSTERS AND ISLANDS AND THEIR REACTION WITH O-2 ON SNO2(110) SURFACES

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 sp ectroscopy (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 Angstrom, Sn metal still is s een at the surface. But when this surface is annealed at 800 Kin 5 x 1 0(-6) mbar O-2 for 20 min, the Sn atoms are totally converted to SnO2. Simultaneously, the deposited Cu atoms become oxidized. The surface c harges up both during LEED and SRPES data acquisition. The clean SnO2( 110) surface shows a 1 x 1 structure. With Cu deposition, the substrat e LEED pattern gradually becomes weaker. With even more copper deposit ed, a Cu(lll)-1 x 1-oriented particle structure appears, indicating co alescence of the Cu islands to 3-dimensional Cu(lll) epitaxy. After su bsequent heating to 500 K, the substrate signal appears again, and we see the SnO2 1 x 1 pattern. In conclusion, Cu atoms quite easily form clusters on the SnO2(110) surface already after a slight heat treatmen t. The results show that this system is quite active towards O-2 gas e xposure, and that the surface conductivity changes during O-2 exposure .