Core-level shifts in bulk alloys and surface adlayers

Abstract

The (initial state) core-level shifts of transition metals in bulk alloys and for bimetallic adlayer systems are calculated and analyzed in terms of extra-and (l-decomposed) intra-atomic contributions. Both the trends and magnitudes of the calculated shifts are consistent with experimental data where they exist. Core-level shifts of the same sign for both constituents are common in both alloy and adlayer systems. The commonly used "charge transfer" model for interpreting core-level shifts is shown to be grossly inadequate, especially for describing the adlayer shifts; for bulk alloys, however, there is a correlation between the shifts and the changes in the d electron count. The results support the view that the bonding in bulk alloys and adlayers is fundaxnentally the same; in particular, there is no evidence for any anomalous charge transfer in adlayer systems. The extraatomic contributions to the adlayer shifts are found to dominate the total shifts for Cu/Rh(001), Cu/Ta(110), and Pd/Ta (110), with the intra-atomic contributions often having the opposite sign compared to the total shift. For the substrate, however, the intra-atomic contributions are relatively more important, suggesting that substrate core-level shifts may provide a better measure of the local chemical e6'ects than adlayer shifts. The relationship of core-level shifts to other physical properties is also discussed.

CO Chemisorption at Metal Surfaces and Overlayers

“…One key surface parameter determining the strength of the bonding turns out to be the energy of the center of the metal d band. This surface property can be obtained from spectroscopical methods either directly with photoemission (UPS) or indirectly through the surface core level shifts [3,4]. Using this, we demonstrate explicitly how our model of the CO chemisorption energy can account for all of the experimental data of Rodriguez and Goodman.…”

“…Our analysis goes in two steps. First, we build on the extensive theoretical insight into the origin of the surface core level shifts by Weinert and Watson (WW) [3] and Hennig, GandugliaPirovano, and Scheffler (HGS) [4]. WW show that the variation in surface core level shifts for metal overlayers is accompanied by a similar shift in the center of gravity of the d bands-at least towards the right in the transition metal series, while charge transfer effects are inadequate for explaining the shifts.…”

First principle calculations of core-level binding energy and Auger kinetic energy shifts in metallic solids

“…For more detailed information on photoelectron spectroscopy and several applications, see [1] and the book by Hüfner [2]. Also, for further discussion about core-level shifts, see for instance [15,[31][32][33]. The structure of this work is as follows: in the theory section we describe the complete screening picture and transition state method schemes for the ab initio computation of core-level shifts, using for example Green's functions methods and supercell techniques.…”

“…For instance, one may consider; the screening of the final state core-hole, the Fermi-level energy reference, inter-atomic charge transfer, intra-atomic charge transfer (sp ↔ d orbital character), and the redistribution of charge due to bonding and hybridization, as discussed by Weinert and Watson [15]. An advantage of using the complete screening picture is that all of the above effects are intrinsic to the ab initio calculations, accounting for both initial (the shift of the on-site electrostatic potential for an atom in different environments) and final state (core-hole screening by conduction electrons) effects directly in the same computation scheme.…”

Neutron scattering studies of nanomagnetism and artificially structured materials

“…Even for very low concentrations of magnetic impurities, sizable ferromagnetism has been observed in the Pd matrix [117,118]. Furthermore, in the case of a well-defined thin film interface, a moment of about 0.3 µ B / Pd atom has been inferred for the first layer in contact with the ferromagnetic material from electronic structure calculations [119] magnetometry data [120,121,122], and X-ray magnetic circular dichroism studies [123]. On the other hand, the magnon spectra show very little effect due to the magnetic proximity effect [124].…”