Atomically resolved electronic structure of pyrite {100} surfaces: An experimental and theoretical investigation with implications for reactivity

Clean pyrite {100} surfaces, generated by cleaving in UHV, were investigate d using scanning tunneling microscopy and spectroscopy for the purpose of u nderstanding the electronic structure at the surface. Calculations of the s urface atomic structure and LEED data support a (100) surface structure tha t undergoes very little relaxation and can be approximated by a simple term ination of the bulk structure along a plane of cleaved Fe-S bonds. UPS spec tra show a well defined peak at similar to 1 eV forming the top of the vale nce band for the near surface. Calculated densities of states for the bulk crystal suggest that this band is comprised primarily of non-bonding Fe 3d t(2g) character and lesser S 3p and Fe 3d e(g) character. Slab calculations predict that the loss of coordination at the surface results primarily in the displacement of Fe 3d(z2)-like surface states into the bulk band gap. E vidence for this surface state is found in low bias STM imaging and normali zed single-point tunneling spectra. Calculations of the LDOS at surface Fe and S sites indicate that the highest occupied state is primarily of 3d(z2) -like character and the lowest unoccupied state is of mixed Fe 3d(z2)-S 3p character. The results predict that due to the dangling bond surface states , Fe sites are energetically favored over S-2 sites for redox interaction w ith electron donors or acceptor species on this surface. Surface redox reac tions are expected to involve the quenching of these high energy dangling b onds, leading to new bonds and surface species, changing the chemical makeu p of the surface.