BBonding in minerals: the application of PAX (photoelectron and X-ray) spectroscopy to the direct determination of electronic structure

Abstract

X-ray photoelectron spectroscopy can be used to measure the ionization energies of electrons in both valence band and core orbitals. As core vacancies are the initial states for X-ray emission, a knowledge of their energies for all atoms in a mineral enables all the X-ray spectra to be placed on a common energy scale. X-ray spectra are atom specific and are governed by the dipole selection rule. Thus the individual bonding roles of the different atoms are revealed by the fine structure of valence X-ray peaks (i.e. peaks which result from electron transitions between valence band orbitals and core vacancies). The juxtaposition of such spectra enables the composition of the molecular orbitals that make up the chemical bonds of a mineral to be determined.Examples of this approach to the direct determination of electronic structure are given for silica, forsterite, brucite, and pyrite. Multi-electron effects and developments involving anisotropic X-ray emission from single crystals are also discussed.KEYwo RD S: X-ray emission spectroscopy, X-ray photoelectron spectroscopy, electronic structure.

Silicon K-edge XANES spectra of silicate minerals

“…The structure and bonding of silicates and aluminosilicates have been studied using x-ray photoelectron spectroscopy (XPS) (Adams et al 1972;Urch and Murphy 1974;Adams et al 1977;Wagner et al 1981Wagner et al , 1982West and Castle 1982;Seyama and Soma 1985, t987;Nefedov et al 1988), Auger electron spectroscopy (AES) (Wagner et al 1981(Wagner et al , 1982West and Castle 1982;Nefedov et al 1988), x-ray emission spectroscopy (XES) (Brytov et al 1979; Pitault et al 1981; Wiech and Kurmaev 1985;Pur-Correspondence to: G.M. Bancroft ton and Urch 1989;Urch 1989), x-ray photoelectron diffraction (XPD) (Evans et al 1979;Evans and Raftery 1980), x-ray absorption spectroscopy (XAS) (Brytov and Romashchenko 1978;Brytov et al 1979), magic-anglespinning (MAS) nuclear magnetic resonance (NMR) spectroscopy (for example, Lippmaa et al 1980;Grimmer et al 1981;Smith et al 1983;Klinowski 1984;M/igi et al 1984;Kinsey et al 1985;Weiss et al 1987;Kirkpatrick 1988;Sherriff and Grundy 1988;Sherriff et al 1991), and molecular orbital (MO) calculation (Tossell 1973(Tossell , 1975Tossell and Gibbs 1977;Dikov et al 1978). MAS NMR, in particular, has become a very powerful techniq...…”

Study of ion beam induced chemical effects in silicon with a downsized high resolution X-ray spectrometer for use with focused ion beams

“…55 A detailed discussion about its origin can be found in several papers, but further theoretical calculations are needed. 56,57 The Kb region of Na 2 SiO 3 shows a similar structure to that of SiO 2 but its ne structure is unresolvable. Kb emission lines offer many more opportunities for chemical speciation studies but their substantially lower intensity compared to Ka lines (intensity ratio of Kb and Ka is 2.4% for silicon 58 ) presents an obstacle.…”

Electronic structure and oxygen bonding in CaSiO3silicate

“…Several spectroscopic methods have been used to measure band structure and the electron density of states (DOS). X-ray emission bands, for example, can provide information on the bonding of different atoms in silicates [6]. Detailed band structure calculations have also been carried out in several alkali silicates for comparison with experimental x-ray photoemission and photoelectron spectra [7].…”