Cooper-minimum effects in the photoionization cross sections of 4d and 5d electrons in solid compounds

We present experimental determinations of the cross section for photoionization for 4d and 5d valence states in transition and noble metals and at the interfaces that these metals form with elemental semiconductors (group IV) in the photon-energy range h=70-200 eV. A description of the technique used to obtain cross sections from photoemission measurements is provided, and a phenomenological discussion of the strong dependence of on the distortion of the initial-state d wave function in the solid environment with respect to the atomic case and in solid-state compounds with respect to pure metals is proposed. A strong reflection of the chemistry involving the d states on the photoionization probability is found, in particular, at the Cooper minimum. The use of photoemission at the Cooper minimum to study interfaces and compounds involving 4d and 5d states is discussed with the support of data relevant to commonly investigated systems, as well as an application to a less-studied refractory-metalSi interface, namely, Mo/Si.