Experimental and theoretical characterization of the structure of defects at the pyrite ${\mathrm{FeS}}_2\left(100\right)$ surface

Defect-free pyrite (100) surfaces were generated and a controlled manipulation of sulfur defect density at these surfaces was performed. Sulfur species of different coordination environments at the surface were probed by $\mathrm{S}$ $2p$ photoemission in combination with theoretical modeling of $\mathrm{S}$ $2p$ core-level shifts. A strict structural assignment of $\mathrm{S}$ $2p$ peaks at the ${\mathrm{FeS}}_2\left(100\right)$ surface in the low defect density regime was achieved. Based on our results, a defect that is related to a surface sulfur vacancy is confirmed to provide the active site for the rapid initial oxidation of pyrite.

Figure 1

$\mathrm{S}$ $2p$ XPS at an excitation energy of $225\mathrm{eV}$ for defect-free and low defect density pyrite (100). Spectra are normalized to the same area. Experimental spectra are shown as crosses; solid lines are the results from peak fitting. (a) Defect-free and (b) low defect density surface after $10\min$ of $200\mathrm{V}$ ${\mathrm{Ne}}^{+}$-sputtering. A new $\mathrm{S}$ $2p_{3∕2}$ feature, labeled $\mathrm{M}$, is generated at a binding energy of $160.95\mathrm{eV}$.

Figure 2

Photon energy dependence of the $\mathrm{S}$ $2p$ photoemission of the defect-free pyrite (100) surface as in Fig. 1a at, from top to bottom, 225, 415, 755, and $960\mathrm{eV}$ photon energy, respectively. All spectra were normalized to the same background; the constant background was then subtracted and the $\mathrm{B}$-component was normalized to the same height for all spectra. The $\mathrm{S}$-component is clearly surface-related as seen from the photon energy dependence. The $+0.1\mathrm{eV}$ shift of the $\mathrm{B}$-component with increasing photon energy is indicated by the solid line.

Figure 3

(Color online). Side-views of different species and structural situations at the ${\mathrm{FeS}}_2\left(100\right)$ surface used for the spectroscopic modeling shown together with their labeling. (a) Defect-free bulk terminated surface. (b) Surface sulfur vacancy, resulting in the sulfur monomer species ${\mathrm{S}}_{\mathrm{M}}$. (c) Situation generated at opposite cleavage face from the surface sulfur vacancy resulting in the ${\mathrm{S}}_{\mathrm{A}}$-species.