Interface effects for metal oxide thin films deposited on another metal oxide .3. SnO and SnO2 deposited on MgO(100) and the use of chemical state plots

SnO and SnO2 thin films have been deposited on MgO(100). They have been characterized by means of ISS, XPS and EELS. ISS shows that both oxides spread on the surface of MgO(100). At low coverages. tin exhibits important shifts in the binding energy (BE) of the Sn 3d(5.2) peak and in its Anger parameter (alpha'). These shifts are produced as an effect of the interaction with the substrate. These results are critically compared within the frame of a chemical state plot with those obtained previously for SnO and SnO2 supported on SiO2 and SnO supported on silver and graphite. It is concluded that for SnO and SnO2 the shifts in the BE and alpha' parameters are mainly due to variations in the relaxation energy of the photoholes rather than to modifications of the initial state of tin Thus. owing to the high sensitivity of the BE and alpha' of tin in very thin films of tin oxide to the influence of the substrate, an accurate measurement of both parameters is necessary for an unanbigous determination of the oxidation state of tin.