Optical studies of dilute gold titanium alloys

Abstract

By optical techniques, we have studied the electronic properties of the Ti impurity which forms a localised virtual bound state (V.B.S.) in Au. Our method involved the use of Beaglehole's differential reflectometer, and measurements were made over the energy range of 0.1 to 5.0 eV, on alloys of concentration in the range 0.7 to 5-5 at.%. The Au:Ti thin film samples were prepared in an ultrahigh vacuum system, Au being evaporated from a conventional resistance heated boat and Ti evaporated simultaneously at the appropriate rate using an electron beam gun. The samples were annealed in the vacuum before any measurement and the electrical resistance was used to monitor the annealing process. The optical data analysis indicates the Ti V.B.S. is broad (half width about 1.0 eV) and lies quite far from the Fermi level (centred about 1.8 eV above the Fermi level), and that only two d-electrons occupy the Lorentzian density of states. The resistivity measurement on our samples also enabled us to find the Ti resistivity as 5.4 ± 2.0 μΩ-cm/at.% at 300 °K. Such a value is appreciably lower than 12.0 μΩ-cm/at.% which has been obtained by White on his wire samples at 4 to 12 °K. Furthermore, our alloy's zero frequency relaxation time is always lower than the d.c. relaxation time by approximately the same proportion as for the host.