X‐ray photoelectron diffraction studies of the surface chemistry of non‐stoichiometric synthetic spinel

Abstract

Angle-resolved XPS data from a synthetic spinel crystal of approximate composition MgO *(3.4)AI20, are reprted and discussed. Strong x-ray photoelectron dieaction (XPD) effects were observed both in argon ion bombarded/annealed surfaces (which were grossly magnesium-deficient) and in chemically etched surfaces prepared by treatment with sodium peroxide at 480°C followed by an acid wash. Many major features of the XPD patterns could be explained using the enhanced forward scattering concept. The relative magnitudes of the XPD modulation of the photoelectron intensity suggest that no more than one-third of the aluminium occupies tetrahedral sites, in accordance with magic-angle-spinning nuclear magnetic resonance experiments, and confirm that the magnesium, in contrast, remains predominantly in the tetrahedral sites. Thin layers of magnesium, cobalt(I1) and chromium(II1) oxides deposited on the crystal surface from nitrate precursors diffused rapidly into the crystal at -llOO°C, with first-order kinetics, but the mixed-oxide surfaces so created showed no evidence of order.

Angle-Resolved X-Ray Photoelectron Studies of Cleavage in Chlorites

“…Magnesium, in contrast, has no nearest neighbor in this direction and its emission intensity is consequently not maximal at this angle. A similar contrast occurs in the spinel structure between the tetrahedral and octahedral ion XPD (Ash and Evans 1993).…”