Photoemission and Auger spectroscopy studies of the interaction of oxygen with zinc

Abstract

Photoemission spectroscopy (u.p.s. and X.p.s.) and Auger Spectroscopy (X-ray induced) have been used to study the oxidation of clean evaporated zinc films. At 300 K, two oxygen species coexist throughout the adsorption process. The major species [O(1s) b.e. 530.0 eV] is characteristic of oxide and is considered representative of a process wherein penetration of Zn layers occurs. The minor species [O(1s) b.e. ≃ 531.8 eV] represents oxygen confined more to the surface region and is electronically dissimilar from oxide. Though performed under u.h.v. conditions, we cannot rule out the possibility that this species is hydroxyl, since for adsorption at 77 K we demonstrate that some molecular H2O appears on the surface at high exposures. Adsorption to saturation at 77 K, followed by warming to 300 K produces less of the oxide phase and more of the minor oxygen species compared to 300 K adsorption. Adsorption at higher temperatures than 300 K increases the amount of oxide formation.Oxygen uptake values are estimated from peak relative intensities. The reliability and model dependent nature of such estimates is discussed. The results indicate that saturation coverage at 300 K is greater than or equal to 2.5 monolayers.The results of the present study are compared with other recent studies and it is concluded that the mechanism of oxide growth is still not fully understood, though it is clearly different from Ni or Fe since for Zn the growth of oxide nuclei is not preceded by chemisorption and induction periods as it is for Ni and Fe.