Core-level subsurface shifted component in a4dtransition metal:Ru(101¯0)

Abstract
Three components have been found in the Ru(101¯0) 3d5/2 core-level spectra. Based on a photoelectron diffraction experiment they have been assigned to emission from the bulk and the first two surface layers. The first layer line is shifted by 480meV from the bulk peak position and the second layer line by 240meV. The relative magnitude of the observed shifts is in good agreement with a simple tight-binding model. The same model would, however, predict clearly observable shifts for other open 4d transition-metal surfaces, where only one shifted component has been reported. Possible reasons for the seemingly anomalous behavior of Ru are discussed.