Nearest-Neighbor Backscattering Effects in Angle-Integrated Photoemission Spectroscopy of Core Levels

We have measured the photomission intensity versus photon energy curves of the Sn $4d_{\frac{5}{2}}$ level in SnS and Sn${\mathrm{S}}_2$ and the In $4d_{\frac{5}{2}}$ and Se $3d$ levels in InSe up to 110 eV above threshold. The structure observed in these curves is mostly due to nearest-neighbor backscattering. This raises the possibility of surface extended x-ray-absorption fine-structure experiments by photomission intensity measurements.