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Abstract

The first detailed study of photoelectron spectra of Sb₂Te₂Se and (Bi_0.7Sb_0.3)₂Se₃ (111) clean and sputtered surfaces is presented as part of an XPS examination of the surface chemistry of these and related materials. The core level binding energies and surface chemical composition have been determined from the XPS data. On substitution of Te by Se in Sb₂Te₃ leading to Sb₂Te₂Se the core level binding energies in Sb and Te increase by 0.3 eV while in Bi₂Se₃ the binding energy of core electrons does not change on replacement of Bi by Sb. The measured core level shifts are caused by changes of the initial state charge distribution and result in increase of average ionicity of bonding in the Sb₂Te₂Se crystal. The surface composition of Sb₂Te₂Se sample calculated from intensities of photoelectron spectra agrees well with the bulk composition of the crystal while (Bi_0.7Sb_0.3)₂Se₃ sample shows enrichment in Bi. The effect of argon ion bombardment on surface composition for various impact conditions has been investigated. The surface enrichment in Sb and Bi for Sb₂Te₂Se and (Bi_0.7Sb_0.3)₂Se₃ sample due to different atomic sputtering yields is observed. It follows from the relative intensities of photoelectron spectra measured at different detection angles that the ordered arrangement of the superficial layers sampled by the XPS method is damaged by sputtering at ion energies as low as 200 eV and doses I > 2 . 10¹⁵ ion/cm².

Keywords: X-ray photoelectron spectroscopy; Substitution effects; Ion sputtering; Sb₂Te_3-xSe_x; (Bi_1-xSb_x)₂Se₃.