Optical Properties of Ag andα-Phase Ag-Al Alloys

Abstract

Reflectance measurements at nearly normal incidence were used to investigate the optical properties and electronic band structure of Ag and dilute alloys of Al in Ag. Sample films were prepared, maintained, and measured in ultrahigh vacuum with base pressures less than ${10}^{-9\mathrm{}}$ Torr. Measurements were made in the spectral range 1.1-11.5 eV. Shifts in the ${\epsilon }_2$ peak at 4.54 eV ($L_3\to L_{2^{\prime }}$) are at one-half the rate expected for the rigid-band model. The implication is that the shielding cloud around the Al impurities saturates the band allowance of two electrons per atom. The weak $L_2\to L_1$ transition, hidden under the $L_3-L_{2^{\prime }}$ transition in pure Ag, shifts to lower energy in the alloys. The transition with ${\epsilon }_2$ peak at 5.73 eV is not shifted by alloying.