The interactions among erbium, oxygen and silicon atoms on a Si(1 0 0)-2x1 reconstructed surface have been studied by means of X-ray photoelectron spectroscopy and Rutherford backscattering spectrometry. Erbium and oxygen were deposited at 600 degreesC on the Si surface and their behavior has been observed after different thermal processes. It was found that at 600 degreesC, the formation of a stable surface complex Er-O-Si is obtained together with Si oxidation; after an 800 degreesC annealing, the amount of oxygen bound to Si decreases and the remaining O atoms are mainly bonded to Er. An abrupt change was observed after 900 and 1000 degreesC annealings. which bury the Er atoms about 60 A below the substrate surface. Our results give some hints to hypotise the O diffusion towards the Si bulk. (C) 2003 Elsevier B.V. All rights reserved.