Conversion Electron Yield XAFS for Ceramics and Metal Alloys

The conversion electron yield (CEY)-XAFS spectra have been compared with those measured by the transmission method for ceramics powders and metal alloys. It has been pointed out from the comparison of Ti K-XAFS spectra of Ti metal foil and sheet that simple cleaning of specimen and elimination of surface oxides are necessary before the CEY-measurement to obtain the bulk information because the CEY method is surface sensitive. The amplitude of the CEY-EXAFS oscillation was somewhat smaller than that of the transmission-EXAFS oscillation for powder and foil samples, suggesting that one should take care of the evaluation of the EXAFS parameters such as the coordination numbers and the Debye-Waller factor on analyzing the local structure using the CEY-XAFS. It has been found from the analysis of both Ni K-XANES and K-EXAFS of NiO powder that the non-stoichiometry δ in NiO1+δ increases in the vicinity of the surface. At such higher energy region as In and Eu K-edge, the CEY method appears to have potential to the XAFS measurements, especially for either samples which cannot be pulverized or the situation where one cannot prepare the samples with adequate concentration. The signal-to-background ratio SB for the CEY-XAFS is also discussed; SB seems to be affected by at least two factors, ie, the Auger electron emission probability and the surface condition of specimen for K-absorption edge, while SB at LIII-absorption edge is mostly small in spite of quite large Auger electron emission probability.