Orientation-resolved 3d_5/2 binding energy shift of Rh and Pd surfaces: Anisotropy of the skin-depth lattice strain and quantum trapping

Incorporating the BOLS correlation algorithm [Y. Sun, J. Phys. Chem. C, 2009, 113, 14696] into high-resolution XPS measurements [J. N. Andersen, et al., Phys. Rev. B: Condens. Matter, 1994, 50, 17525; A. Baraldi, et al., New J. Phys., 2007, 9, 143] has produced an effective way of determining the 3d _5/2 energy levels of isolated Rh(302.163 ± 0.003 eV) and Pd (330.261 ± 0.004 eV eV) atoms and their respective bulk shifts (4.367 and 4.359 eV) with a refinement of the effective atomic coordination numbers of the top (100), (110), and (111) atomic layers (4.00, 3.87, and 4.26, respectively). It is further confirmed that the shorter and stronger bonds between under-coordinated atoms induce local strain and skin-depth charge-and-energy quantum trapping and, hence, dictate globally the positive core level binding energy shifts.