X-Ray Photoelectron Spectroscopy (XPS) used as a structural and chemical surface probe on aluminosilicate minerals
Biino, Giuseppe G.; Gröning, Pierangelο
European Journal of Mineralogy Volume 10 Number 3 (1998), p. 423 - 438
published: Jun 22, 1998
manuscript accepted: Feb 9, 1998
manuscript received: Feb 12, 1997
ArtNo. ESP147051003003, Price: 29.00 €
Abstract In surface science investigations, it is often required to determine the elemental composition and the chemical bonding states of the outermost atom layers (called surface) of a solid. X-ray Photoelectron Spectroscopy (XPS) detects photoelectrons generated in the outermost atom layers, this providing a valuable tool for studying the chemical composition and chemical environment of elements at the surface of solids. The aim of this study is to provide a systematic investigation of the surface of some aluminosilicate minerals by XPS. To accomplish this task, we investigated the XPS spectra of single crystals of andalusite, kyanite, pyrope and K-feldspar and pressed powder pellets of andalusite and pyrope. XPS yields accurate and reproducible chemical information on the near surface of these minerals. Although, the chemical composition is close to stoichiometry but the composition of the cleaved kyanite surface is richer in Si. This experimental observation is consistent with the established cleavage model. The aluminosilicate mineral surfaces are made up of adsorbed C-enriched material. The shift in kinetic energy of photoelectrons makes it possible to derive qualitative information on atomic structure, but surface charging leads to difficulties in interpreting chemical states. Therefore, charging corrections in minerals are discussed to some extent. The O1s peak can be used as indicator of the chemical environment of oxygen in silicates. We were able to split the O1s peak into its main components: Al-O-Si, Si-O-Si, non-bridged oxygen and contamination layers (adventitious material). The C1s peak gives valuable information on surface-atmosphere interactions and provide evidences for microinclusions of graphite. The presence of a thick C-rich cover poses some problems for the interpretation of Scanning Force Microscopy (SFM) images collected in air or in liquid. For a quantitative interpretation of XPS spectra a larger database is necessary coupled with information collected with other surface sensitive equipment.