High-resolution inverse-photoemission study of the Pd(111) surface

We present high-resolution inverse-photoemission spectra for the clean Pd(111) surface. For what we believe to be the first time we clearly resolve the anticipated Shockley state at the bottom of the $L_{2\mathcal{’}}$$L_1$ band gap. This state is found to have a binding energy of 1.3 eV above the Fermi level and an effective mass of approximately 0.3$m_e$. We further observe the n=1 image state and find that it has a binding energy of 0.5 eV with respect to the vacuum level and an effective mass of 1.0$m_e$. Comparison with the phase model shows good agreement with these measured binding energies. We find that these measurements indicate that the image plane is close to the jellium edge.