Surface structure of sphalerite studied by medium energy ion scattering and XPS

The reactivity of high-Fe containing sphalerite (Zn1-xFexS), the major source of Zn, is of great interest for industrial applications. Since the initial reactivity depends on the physical and chemical properties of the surface, it is important to understand the structure of cleaved and fractured surfaces. Zn1-xFexS zincblende (1 1 0) oriented samples cleaved in air and in vacuum were studied with medium energy ion scattering (MEIS) in order to study surface relaxation and reconstruction associated with the possible formation of S dimers. The experimental results are presented together with ion scattering Monte Carlo simulations that have been performed using the different models of the surface structure. The MEIS blocking patterns are different for the air- and vacuum-cleaved specimens. Models for the air-cleaved samples found S atoms in the first layer that are relaxed outwards by 0.08 Å and Zn(Fe) atoms relaxed inwards by 0.51 Å, with some lateral translation of both species. Results for the vacuum-cleaved sample indicate S atoms have been displaced laterally by 0.5 Å at the surface. X-ray photoelectron spectroscopic (XPS) measurements provide evidence for a high binding energy species indicative of S-S bonds in the near-surface region that are consistent with the ion scattering structural data for both cleaving protocols.