Piezoreflectance and Electronic Structure of Alloys of Copper with Polyvalent Solutes
Piezoreflectance and other optical measurements have been made on other optical measurements have been made on a phase alloys of Cu with Zn Ga, Al, In and Ge. The samples were evaporated films deposited on the face of a resonant oscillator assembly. The application of this type of strain transducer to piezoref-reflectance alleviates systematic errors and allows the response to pure shear strains to be distinguished, even in amorphous materials, using the polarisation dependence of the results. The energies of the d band -> Fermi level threshold, the interconduction band threshold, and the L2' -> L1 critical point transition were determined for the alloys. Previous optical studies using more conventional methods either have not been able to resolve these features or have not located them with accuracy comparable with piezoreflectance. With increasing alloy concentration the d band threshold is found to shift slowly to higher energies, the inter-conduction band transitions more rapidly to lower energies. Zn impurities produced much smaller shifts than the others, indicating the importance of interactions between impurity d states and the d and conduction states of the host. Significant differences were found between the isovalent solutes Ga and A1. In concentrated alloys with Zn, Ga and Al the interconduction band threshold tended to a common value of about 2.5 eV. This lack of simple dependence on e/a, the electron per atom density in the alloy, is relevant to the understanding of the electronic structure of the Hume-Rothery alloys and the regularity of the [alpha] phase boundary.