Surface properties of indium-doped Cd2SnO4 ceramics studied by EELS and photoemission spectroscopy

Ceramic samples of indium-doped dicadmium stannate (Cd2SnO4) have been studied over the doping range 0.5-2.0 at% In by electron energy loss spectroscopy (EELS) and ultraviolet and X-ray photoemission spectroscopy (UPS and XPS). The samples were prepared from SnO2 and Cd1-xInxO, which was itself made from CdO and In2O3. The maximum surface plasmon energy is around 0.450 eV. The carrier concentration derived from the plasmon energy is always lower than that estimated from the bulk dopant concentration. The atomic percentages of both cadmium and tin on the surface before annealing, determined from XPS, are lower than those in undoped Cd2SnO4, giving evidence for the substitution of In3+ ions on both Cd2+ and Sn4+ sites. XPS shows a pronounced decrease in the surface concentration of segregated indium after annealing under UHV conditions. He(I) UPS shows a well defined conduction band feature with a higher intensity than that for undoped samples. It is evident that the lower edge of the valence band shifts towards higher binding energy as the doping level increases.