High Resolution Core- and Valence-Level XPS Studies of the Properties (Structural, Chemical and Bonding) of Silicate Minerals and Glasses

Core-level and valence-level X-ray Photoelectron Spectroscopy (XPS), developed in the late 1950’s and 1960’s by Siegbahn and coworkers (Siegbahn et al. 1969; Carlson 1975; Barr 1993; Fadley 2010) has become an invaluable tool over the last 40 years for studying mainly the surface properties and reactivity of a wide range of minerals, predominantly oxides (for reviews, see: Heinrich and Cox 1994; Chambers 2000; Salmeron and Schlogl 2008, and references in Bancroft et al. 2009; Newburg et al. 2011), sulfides (for reviews, see Hochella 1988; Bancroft and Hyland 1990; Nesbitt 2002; Murphy and Strongin 2009) and silicates (for a review see Hochella 1988; references in Biino and Groning 1998; Oelkers 2001; Zakaznova-Herzog et al. 2008). The large majority of these studies have focused on the first few surface monolayers of the minerals because of the surface sensitivity of the technique (~2–20 monolayers for photon energies of ≤ 1486 eV (Hochella 1988; Nesbitt 2002), and in many such cases, XPS has become the technique of choice for surface studies. Silicate XPS studies generally have focused on three surface applications outlined by Hochella (1988): (1) studies of the oxidation state of near surface atoms (e.g., Fe); (2) studies of sorption reactions on mineral surfaces; and (3) studies of the alteration and weathering of mineral surfaces. Fewer reports have focused on the fourth application of Hochella (1988), the study of the bulk atomic structure and chemical state properties of minerals and glasses. This is surprising perhaps, because the large majority (usually >90 %) of XPS line intensities comes from the bulk mineral in XPS studies using the typical laboratory Al K α X-ray sources (1486.6 eV). To emphasize this point, the surface S 2 p peaks from the …