Al-Sn layer structures were prepared by simultaneous evaporation of Al and Sn onto predeposited Al layers prepared on SiO2-covered Si wafer substrates, at a substrate temperature of 470 K and an oxygen partial pressure of 3 X 10(-3) Pa. The chemical state, the morphology and the lateral distribution of the species formed on the surface were studied by high resolution XPS and STM, respectively, while the cross-section of the layer system was investigated by transmission electron microscopy. Our present results confirm that Sn segregates to the surface of the growing film and partly forms fine Sn grains covered with a thin SnO2 layer on the surface of the growing Al crystals together with an Al2O3 phase.