SURFACE AND INTERFACE ANALYSIS Surf. Interface Anal. 2003; 35: 256–262 Published online in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/sia.1523 Characterization of Sb 2 O 3 subjected to different ion and plasma surface treatments R. Reiche, 1 J. P. Holgado, 2 F. Yubero, 2 J. P. Espinos 2 and A. R. Gonzalez-Elipe 2* 1 Leibniz-Institut f ¨ ur Festkoerper- und Werkstoffforschung Dresden, Postfach 270016, 01171 Dresden, Germany 2 Instituto de Ciencia de Materiales de Sevilla (CSIC-Univ. Sevilla), Dept. Q. Inorg ´ anica, Avda Am ´ erico Vespucio, s/n 41092 Sevilla, Spain Received 28 August 2002; Revised 14 November 2002; Accepted 18 November 2002 This paper presents a study of Sb 2 O 3 subjected to oxygen plasma and to ion beam bombardment (Ar + and O 2 + ions of 4 keV) by x-ray photoelectron and reflected electron energy-loss spectroscopies. Changes in stoichiometry (i.e O/Sb ratio) and oxidation state of Sb have been detected and correlated with the chemical and ballistic effects of the beams used for alteration of the Sb 2 O 3 surface. Thus, oxygen plasma treatments lead to a significant oxidation of the surface layers of this material with the formation of up to 51% Sb 5+ species as found by Sb 4d curve-fitting analysis. By contrast, O 2 + ion bombardment only produces a mild oxidation of the target with the formation of ∼13% Sb 5+ species. Argon ion bombardment induces a complex process where Sb 5+ and Sb 0 species are formed simultaneously. This result has been discussed in terms of a disproportionation reaction of the type Sb 3+ → Sb 5+ + Sb 0 . The changes in the electronic properties of the treated material are consistent with the loss upon oxidation to Sb 5+ of the valence states associated to the 5s 2 electron pair of antimony. Approximate shapes of valence bands for Sb 2 O 3 and Sb 2 O 5 pure compounds have been extracted by applying factor analysis to valence band spectra of Sb 2 O 3 subjected to different ion and plasma treatments. Copyright  2003 John Wiley & Sons, Ltd. KEYWORDS: low-energy ion bombardment; antimony oxide; plasma treatment; XPS; REELS; factor analysis INTRODUCTION Antimony oxide is a very attractive material because of its interesting applications as catalysts, gas sensors or mixed- oxide film resistors. 1–5 The performance of this material for these applications relies on the changes in the oxidation state of Sb according to the different conditions of operation. In antimony oxide, the transformation between Sb 5C and Sb 3C oxidation states is relatively easy and its magnitude and direction depend on the atmosphere and type of thermal treatments. In particular, both oxidation states seem to be involved in the redox processes that control the efficiency of this material as an oxidation catalyst. 2 Despite that interest, not too many characterization stud- ies by x-ray photoelectron spectroscopy (XPS) of antimony oxides are available in the literature. 1–8 The more recent data by this technique refer to mixed oxides, e.g. to antimony- doped SnO 2 . 6–8 Very likely this is due to the difficulty of getting pure and well-characterized antimony oxide materi- als (i.e. Sb 2 O 3 and/or Sb 2 O 5 ) that could be used as reference compounds and to an intrinsic problem of analysis by XPS due to overlap of the most intense photoemission lines of oxygen (O 1s) and antimony (Sb 3d 5/2 ). L Correspondence to: A. R. Gonzalez-Elipe, Instituto de Ciencia de Materiales de Sevilla (CSIC-Univ. Sevilla), Dept. Q. Inorg´ anica, Avda Am´ erico Vespucio, s/n 41092 Sevilla, Spain. E-mail: agustin@cica.es Contract/grant sponsor: Ministerio de Cienciay Tecnolog´ ıa (Spain); Contract/grant number: MAT 2000-1505-C02-01. In this paper, we present a XPS study of a reference Sb 2 O 3 single-crystal material that is subjected to plasma and ion beam bombardment treatments. The motivation of this study is twofold. On the one hand, we want to get some basic information related to the electronic band structure of this compound with well-characterized specimens. On the other hand, we are interested in knowing the changes in stoichiometry, the formation of new oxidation states and the change in composition that are induced by ion bombardment and plasma treatments. This second motivation is of interest either for the deposition of different materials on antimony oxide used as a substrate or for the preparation of antimony oxide thin films by means of methods involving ion and/or plasma-assisted processes. Moreover, this system provides an interesting case for comparison with the numerous studies on preferential removal of oxygen from oxide materials subjected to ion bombardment. 9–15 In this respect, besides considering the changes in stoichiometry upon ion beam and plasma treatments, the paper also addresses the associated changes in electronic structure. Valence band photoemission and reflection electron energy-loss spectra (REELS) for antimony oxide under the different conditions are analysed for this purpose. In fact, transformation of Sb 3C into Sb 5C in antimony oxide implies the loss of valence band states associated with the so-called 5s 2 electron lone pair, 16,17 a feature typical of the post-transition element compounds (Ge, Sn, Pb, Sb, Bi, etc.) that confers to them relatively common chemical properties. Copyright  2003 John Wiley & Sons, Ltd.