ANALYSIS OF OLS CORE-LEVEL OF P-TYPE AND N-TYPE HIGH-T(C) COPPER OXIDES - EVIDENCE FOR A DIFFERENT NATURE OF CARRIER DOPING

A detailed analysis of the O1s core-levels of p- and n-type high-Tc copper oxides is reported. The binding energies of O1s core-level in La2-xSrxCuO4 and Nd2-xCexCuO4 are found to be different. We also find that, for the p-type La2-xSrxCuO4, the O1s peak shifts towards lower binding energy when hole-carriers are introduced, while, for the n-type Nd2-xCexCuO4, the O1s peak shifts towards higher binding energy when electron-carriers are introduced. Taking into account the different crystal structures and the chemical environment of oxygen sites, our observations are analyzed and explained consistently. It follows that, we are able to understand why holes (electrons) can be doped into p- (n-) type high-Tc copper oxides. The results also confirm that p- and n-type high-Tc copper oxides are quite distinct in nature.