Plasma resonance of binary amorphous and crystalline Al-transition metal alloys: Experiments and ab initio calculations

We report on measurements of the volume plasmon loss energy EP by electron energy loss spectroscopy of binary amorphous Al-(Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Y, Pd, Ce) alloys. In these systems the measured EP can be described by an effective valence of the transition metal independent of the particular transition metal. By exploiting ab initio calculations for the crystalline counterparts in the case of Al-(Ti, V, Fe, Ni) we show that this behavior can be understood in terms of the full dielectric function taking into account intra- and interband transitions mainly due to the presence of d-states close to the Fermi energy. This is validated by the comparison with published experimental data on binary Al systems with the non-transition metals Be, Mg, Ca, and Zn. Due to the absence of composition-dependent structural phase changes, amorphous alloys are found to be model-like systems for studying the influence of interband transitions on the plasma resonance.