A c-axis oriented thin film and a high-density sintered pellet of ${\mathrm{MgB}}_2$ have been studied by x-ray photoemission spectroscopy, and compared to measurements from MgO and ${\mathrm{MgF}}_2$ single crystals. The as-grown surface has a layer which is Mg-rich and oxidized, which is effectively removed by a nonaqueous etchant. The subsurface region of the pellet is Mg deficient. This nonideal near-surface region may explain varied scanning tunneling spectroscopy results. The ${\mathrm{MgB}}_2$ core level and Auger signals are similar to measurements from metallic Mg and transition-metal diborides, and the measured valence band is consistent with the calculated density of states.

• Received 7 March 2001

DOI:https://doi.org/10.1103/PhysRevB.64.052510