Surface-shifted core levels inMo3Si (100) and (110)

High-resolution photoemission studies of core levels in ${\mathrm{Mo}}_3$Si have been carried out using synchrotron radiation. Surface-shifted Si 2p components were observed on annealed (100) and (110) crystal faces and were unambiguously identified in adsorption experiments of hydrogen and oxygen. The surface core-level shifts were extracted using a curve-fitting procedure. For the (110) surface one shifted component was identified having a surface shift of -1.02(1) eV. For the (100) surface two shifted components were found to be necessary in order to model the experimental spectrum, the stronger component having a shift of -0.68(2) eV and the weaker a shift of -1.03(4) eV. No surface-shifted components could be identified in the Mo 4p photoelectron spectrum. Upon oxygen adsorption a chemically shifted Si 2p component was observed, indicating silicon oxidation, while no chemically shifted component appeared in the Mo 4p spectrum. In the Si 2p spectrum pronounced photoelectron-diffraction effects were observed both as a function of photoelectron kinetic energy and emission angle. These findings are presented and discussed.