Optical studies of dilute gold nickel alloys

Abstract

Changes in the reflectivity of gold on alloying with impurity concentrations of transition metals indicate the presence of very strongly scattering virtual bound states near the Fermi level. The experimental determination of these changes in reflectivity involves a modulation technique where pure metal and alloy samples alternately act as reflecting elements in an infra-red spectrometer. Phase sensitive detection then allows ΔR to be measured accurately from visible wavelengths out to 13 μm in the infra-red, with the elimination of several important systematic errors. Kramers-Kronig analysis to generate files of the dielectric constant then allows the response of the medium to be dissociated into an interband part, a Drude conduction electron background and virtual bound state effects characteristic of the alloy. A model describing the localized impurity d-states in terms of a Lorentizian shaped density of states has been used to interpret results specific to gold/nickel alloys. In addition, a generalized Friedel model for a dilute alloy with cellular disorder allows the calculation of virtual bound state parameters from a theorectical point of view, and preliminary results show good agreement with the values measured experimentally.