Highly under-coordinated atoms at Rh surfaces: interplay of strain and coordination effects on core level shift

The electronic structure of highly under-coordinated Rh atoms, namely adatoms and ad-dimers, on homo- metallic surfaces has been probed by combining high-energy resolution core level photoelectron spectroscopy and density functional theory calculations. The Rh3d(5/2) core level shifts are shown to be proportional to the number of Rh nearest-neighbours ( n = 3, 4 and 5). A more refined analysis shows that the energy position of the different core level components is correlated with the calculated changes of the individual inter-atomic bond length and to the energy changes of the d-band centre, which is known to be a reliable descriptor of local chemical reactivity.