Electronic effects at interfaces in Cu-Cr, Mo, W, Ta, Re multilayers

Interfacial electronic effects between Cu and the transition metals Cr, Mo, W, Ta, Re, are investigated by determining the strength of the white line absorption resonances on the L,,, edges of Cu in Cu{sub 5}/TM{sub 5} multilayers. X-ray absorption (XAS) was performed to study the white lines, which are directly related to the unoccupied states of Cu in the multilayers. The metallic multilayers are 2 mn in period and 200 mn in total thickness. Each period contains 5 monolayers of Cu and 5 monolayers of the transition metal: 40% of the atoms are at interfaces. These material pairs form ideal structures for the investigation of interfacial electronic effects as they form no compounds and exhibit terminal solid solubility. Only weak white lines are observed on the L3,2 edges of Cu since all the d-orbitals are filled. In the Cu/TM multilayers, however, we observed enhancement of the Cu white lines. We attribute this to the charge transfer from the `interfacial Cu atoms` d-orbital to the transition metal layers. Analysis of the white line enhancement enables calculation of the charge transfer from the Cu to the transition metal. Cu shows a charge transfer of about 0.03 electrons/interfacial Cu atom in Cu/Cr, 0.064 in Cu/Mo, 2048 0.35 in Cu/Ta, 0.17 in Cu/W , and 0.23 in Cu/Re. This charge transfer is consistent with the enhanced absorption energy of Cu on these materials as observed in thermal desorption experiments