Quantum well states in thin (110)-oriented Au films and k-space symmetry

We present electron diffraction and electron photoemission results for thin Au films grown on Nb(100) in a hexagonal close-packed stacking sequence, which is unusual for Au. Strong d-band [48] quantum size effects occur in photo-electron spectroscopy from 5-26 monolayer thick (11 (2) over bar0) oriented Au films whose confined direction ([11.0]) is not perpendicular to any face of the bulk Brillouin zone. Also in this case, the energetics of the quantum well states can be explained by a discretisation of the bulk band structure corresponding to the quantum well. However, the bulk states corresponding to the quantum well states do not lie in the confined direction of the first bulk Brillouin zone, contrary to what is required by the quantum well. This can be remedied by the construction of a layer symmetry adapted Brillouin zone, which is consistent with the symmetry of the quantum well but different from the bulk one. We subsequently determine, for the first time, the k(parallel to) periodicity of the quantum well states from their measured E(k(parallel to)). This periodicity proves to be consistent with the newly introduced Brillouin zone.