The optical properties of alpha-phase Cu-Zn, Cu-Ga, Cu-Ge and Cu-As alloys

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Abstract
Absorption spectra of bulk samples of α-phase Cu-Zn, Cu-Ga, Cu-Ge and Cu-As alloys have been measured at photon energies from 1.7 to 5.9 eV, using polarimetric techniques in ultra high vacuum. Comparison of the results with band calculations and with the spectrum of pure Cu alloys a reliable identification of the various peaks and edges, and suggests the following interpretation. The d band associated with the Cu atoms is considerably narrowed in Cu-Zn alloys, but this narrowing is much less marked in the other systems. The movement of the Fermi level with solute concentration is in good agreement with Friedel's theory. The energy of the direct transition L2, to L1u is reduced in the alloys by an amount which depends on the e/a ratio. In Cu-Ge this transition is partly masked by indirect transitions involving scattering by impurities, an effect which occurs even more strongly in Cu-As. This interpretation is compared briefly with conclusions derived from similar work on Ag-In alloys, from soft X-ray spectroscopy and from photoemission experiments