Optical Absorptance and Thermomodulation Studies of Several A-15 Compounds

摘要

The purpose of this work was to investigate the optical properties of several high T/sub c/ compounds in the form of sputtered films. The measurements are used toward this end: optical absorptance (using a calorimetric technique near 4.2K), which yields (after Kramers-Kronig analysis) the complex dielectric function, and thermoreflectance (which measures the change in reflectance in the optical range when a 1 to 10 exp 0 K temperature wave is applied), performed at two ambient temperatures (80 and 300 exp 0 K), yielding the differential dielectric function. The sputtered films included Nb sub 3 Ge, Nb sub 3 Al, V sub 3 Ga and Nb sub 3 Ir. It is noted that Nb sub 3 Ir is not a high T/sub c/ superconductor. The thermoreflectance on the bulk samples V sub 3 Si, V sub 3 Ge and single crystal Cr sub 3 Si were not performed because the samples were not in the form of thin films. The thermomodulation studies are correlated with the absorptance measurements in comparison to band structure calculations. When thermomodulation studies are performed on semiconductors, these studies yield information about critical points, but studies on metals indicate that Fermi-level transitions become important. It is thought that A-15 structured compounds, which have a high density of electron states around the Fermi level, will produce spectra due to this high density of states. Procedures and results are detailed. (ERA citation 08:046748)