Optical properties of metals and alloys: Au, Ag, FeRh, AuA12, and PtA12

Date
1987
Authors
Chen, Liang-Yao
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Advisor
David W. Lynch
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Physics and Astronomy
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Physics and Astronomy
Abstract

We designed and constructed a new type of scanning photometric ellipsometer, with polarizer and analyzer both rotating synchronously at rotation rates of [omega][subscript] o/2 and [omega][subscript] o (f[subscript] o = 51 Hz), for the purpose of measuring the dielectric functions of our samples. The mechanical and electrical design, alignment, calibration and error reduction of the system are discussed in detail;We made measurements of the free-electron dielectric function of Ag and Au films in air and immersed in dielectric liquids of different refractive indices. We explained the "anomalous" data for films, seen as the same by Gugger et al.[superscript]58, with an effective medium model by assuming the liquid penetrates all, or most, of the inter-grain regions within the optical penetration depth, but for crystals by assuming an oxidized overlayer exists on the surface after sample preparation. The dielectric functions of "ideal" Ag and Au sample were obtained from fits with an effective medium model;We performed measurements of the dielectric functions for FeRh alloys with 48%, 50%, 52%, and 54% Fe concentrations between 25 and 125°C in the 1-3-eV range. Results show that the band structure of FeRh is not drastically affected at the antiferromagnetic (AF) - ferromagnetic (F) phase transition, less than band structure calculations indicated. Therefore, the large change in the electronic specific heat between the AF and F phases can be attributed primarily to a magnetic contribution rather than to a change in the density of electronic states at the Fermi surface;Finally, we measured dielectric functions of AuAl[subscript]2 and PtAl[subscript]2 alloys in the 1.5-5.5-eV range. The spectra of reflectivity, absorption, energy loss function, and joint density of states were obtained and discussed in detail. The onsets of interband transitions were determined by least-squares fitting to the absorption edges in the spectra of the joint density of states, which could be attributed to transitions between only the s and p bands for both materials. The remaining stronger absorption above the absorption edges can be attributed to transitions between the s and p bands for AuAl[subscript]2 but to transitions between both the s and p bands and the d and s-p bands for PtAl[subscript]2 by means of the band structures. ftn*DOE Report IS-T-1342. This work was performed under contract No. W-7405-Eng-82 with the U.S. Department of Energy.

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