Preparation, Structure, and Orientation of Pyrite FeS2{100} Surfaces: Anisotropy, Sulfur Monomers, Dimer Vacancies, and a Possible FeS Surface Phase

Abstract

Sulfur dimer (S22–) terminated pyrite FeS2{100} surfaces with a low energy electron diffraction (LEED) pattern of 2 × 1 symmetry are reported. The 2 × 1 symmetry correlates with the orientation of the anisotropic surface structure and external symmetry of macroscopic striations on the pyrite cube face. The basic condition to form these surfaces is a mild 200 V Ne+ sputter-cleaning procedure followed by a 570 K anneal of the sample in a 10–7 Torr S2(g) atmosphere. Controlled amounts of surface sulfur monomers (S2–) can be introduced by mild sputtering of the sulfur dimer terminated surfaces. At low monomer concentrations the surface displays the same characteristic 1 × 1 LEED pattern as that for fracture-generated surfaces. With increasing sulfur depletion, a (1/√2 × 1/√2)R45° LEED pattern emerges, and soft X-ray photoelectron spectroscopy (XPS) results show a sulfur dimer deficient near-surface region and a new high binding energy sulfur spectral component suggesting the presence of local coordination env...