Core level photoemission study of polycrystalline MgB2

X-ray photoemission measurements have been made on Mg 2p and B 1s core levels from MgB2 as well as on the O 1s core level from the contaminant oxygen. The motivation for this study came for the discrepancy in the reported papers on the energy values of the B 1s and Mg 2p core levels, ostensibly due to the oxygen, present as an impurity, reacting and forming oxides and other compounds. Sputtering leads to a significant reduction of oxygen on and in the sample. The in situ sputter-cleaned sample gives the best results. The measurements are compared with results reported earlier and discrepancies discussed.