Measurements of white lines in transition metals and alloys using electron energy loss spectrometry

Abstract

This thesis addresses the interpretation of the peaks known as found at the onsets of the L2 and L3 absorption spectra of 3d and 4d transition metals and alloys. These peaks arise from excitations of 2p core electrons to unoccupied outer d states at transition metal atoms. Recent work has suggested that differences in white line intensities observed between pure transition metals and associated compounds may be used to infer changes in the occupancies of the corresponding d states local to a given atom species. These prior studies, however, have focused on compounds of only a few transition metals. A systematic investigation of the relationship between white line intensity and d-state occupancy for 3d and 4d transition metals had not yet been done. In this work an experimental analysis of the white lines for the 3d and 4d transition metals was carried out using electron energy loss spectrometry (EELS), and a linear decrease in white line intensity with increasing d state occupancy was found for both transition series. These results suggest that the intensities of the white lines reflect the occupancies of the outer d states in 3d and 4d transition metals, which are known to increase linearly with atomic number. In addition, these empirical correlations provide a straightforward method for measuring changes in 3d or 4d state occupancy. In an application of this work, L2,3 spectra were measured for a number of binary copper alloys, Fe-Co alloys of varying composition, and several binary nickel alloys. Significant changes in the intensities of the white lines were observed in some cases. Changes in 3d occupancies inferred from these measurements were in agreement with other measurements and density-of-states calculations from the literature where available.