EELS AND AES TRANSITIONS STUDY OF CLEAN AND O, C, H2O AND CH3OH CONTAMINATED NB(110) SURFACES

The energy electron loss spectra (EELS) and the Auger electron spectra (AES) of the clean and C, O, H2O and CH3OH contaminated surfaces of Nb(110) have been studied. The clean surface presents a loss structure at 8.3 eV which changes to 6.8-7.21 eV due to an excitation implying the O(2p) orbital. With the C contaminant the loss occurs at 5.8 eV. The surface and volume plasmons of the clean surface at 17.6 eV energy shifts to 19.5 eV for all the contaminants, due to the disappearance of the surface plasmon. All contaminants reduce the density of the Nb 4d electrons as revealed by the intensity of the M23N45N45 Auger transition at 25 eV energy. The most drastic changes are produced by water adsorption under electron bombardment. The M23N45N45 transition disappears, and instead of it, a new structure at 19 eV energy increases in intensity. This structure is explained as an Auger transition implying electrons of the O(BV). C and C + O contaminants also suppress the 25 eV transition. It is also shown that e- bombardment induces a strong oxidized state. The C + O AES spectrum presents a transition in the region of 19-22 eV energy. The low energy side is related to the O adsorption and the high energy region to the C adsorption. Methanol and water are dissociated as methoxy and hydroxyl radicals respectively. © 1990 Pergamon Press plc.