Core Level Shifts
A core level shift (CLS) is the change in binding energy of a core electron, measured by X-ray photoelectron spectroscopy, when an atom’s chemical environment changes relative to a reference such as the pure metal. In alloys, CLSs respond to composition, local coordination, lattice strain and chemical order, and they can be computed with density functional theory from total energy differences between core-ionized and ground states. See also Bimetallic surfaces and X-ray absorption spectroscopy.
Core level shifts as a probe of B2 ordering in Cu-Pd alloys (2015)
Boes et al. measured the Cu 2p3/2 CLS across the full composition range of Cu1-xPdx composition spread alloy films and found a linear decrease with Pd content except for an anomalous deviation between about x = 0.35 and 0.56, where the ordered B2 phase forms at 800 K (Boes et al. 2015). The anomaly vanished after He+ sputtering and returned on annealing. Complete screening DFT calculations showed the Cu CLS depends roughly linearly on the number of Cu-Cu nearest neighbors, so disordered FCC (more Cu-Cu neighbors) gives a less negative average shift than ordered B2, and lattice contraction plus excess Cu in nonstoichiometric B2 explained the observed trend. Summary: boes2015.