Electron energy loss spectroscopy study of nickel, chromium and a nickel-chromium alloy

Electron energy loss spectroscopy (ELS) spectra have been obtained from polycrystalline Ni, Cr and a Ni-Cr alloy (nichrome) using primary electron energies ranging from 100 to 1150 eV. Loss features due to the surface and bulk plasmon excitations are present in the ELS spectra from each surface as well as a number of smaller features that arise from interband transitions. The ELS spectra obtained from nichrome cannot be reproduced by superposing the pure metal ELS spectra in proportion to the atomic fractions of Ni and Cr in the alloy. The main differences between the calculated and the experimental alloy spectra are an overestimation of the contributions from the plasmons with a concomitant underestimation of the interband transitions in the superimposed spectra. This suggests that the probability for surface plasmon excitation is lower for the Ni-Cr alloy than for the pure metals. The increased contribution from interband transitions results in more Ni-like alloy spectra, since Ni has a higher number of d electrons that can give rise to interband transitions in the energy-loss region under investigation. However, the interband transitions in the alloy are shifted relative to the pure Ni spectra indicating that alloy-specific states have been created. These findings reveal that the electronic structure of the Ni-Cr alloy is altered by chemical bonding interactions between the Ni and Cr atoms demonstrating the usefulness of ELS for this application