Interfacial Electronic-Charge Transfer and Density of States in Short-Period Cu/Cr Multilayers

摘要

Nanometer period metallic multilayers are ideal structures to investigate electronic phenomena at interfaces between metal films since interfacial atoms comprise a large atomic fraction of the samples. The multilayers studied were fabricated by magnetron sputtering and consist of bilayers from 1.9 nm to 3.3 nm. X-ray diffraction, cross-section TEM and plan-view TEM show the Cu layers to have a BCC structure Cu in contrast to its equilibrium FCC structure. The electronic structure of the Cu and hte Cr layers in several samples of thin Cu/Cr multilayers were studied using x-ray absorption spectroscopy (XAS). Total electron yield was measured and used to study the white lines at the CuL_2 and L_3 absorption edges. The white liens at the cu absorption edges are strongly related to the unoccupied d-orbitals and are used to calculate the amount of charge transfer between the Cr and Cu atoms in interfacial Cr atoms. In the Cu XAS spectra we also observe a van Hove singularity between the L_2 and L_3 absorption edges as expected from the structural analysis. The absorption spectra are compared to partial density of states obtained from a full-potential linear muffin-tin orbital calculation. The calculations confirm the presence of charge transfer and indicate that it is localized to the first two interfacial layers in both Cu and Cr.