Piezoreflectance of Pure and Reacted Films of Gadolinium and Lutetium

Abstract

The reflectance and polarised piezoreflectance of gadolinium, lutetium, oxidised gadolinium, oxidised lutetium and hydrogenated lutetium has been measured from 1.5 to 6 eV. The measurements were made in situ in an ultra high vacuum chamber on thin films evaporated onto a single crystal quartz strain transducer. The reflectance was measured using a V-W configuration of the optics internal to the vacuum chamber. The reflectance of the two metals agreed with previous measurements and it was concluded that there was a large onset of sp → d band transitions below 3 eV with the sp and d bands being more widely separated in lutetium. The two metals had apparently similar piezoreflectance spectrum. The hydrostatic response of the modulated dielectric constant had an overall shape that was found to arise from a constant shift of the experimental joint density of states curve, implying a constant negative average deformation potential for sp → d transitions with energy. Following large exposures to oxygen, both metals retained essentially metallic properties in the bulk, with only a very dilute concentration of oxygen. Significant movement was seen in the critical point features under the influence of the oxygen implying movement of the electronic bands. A high energy feature appeared in the oxygenated spectrum of gadolinium at 4.55 eV and moved down with further oxidation. This was assigned to transitions from the oxygen 2p bands which had hybridized with the metal sp bands. The hydrogenated lutetium was found to be contaminated by substrate hydrogen. Significant changes in the reflectance and piezoreflectance were measured and agreed with predictions. The concentration of hydrogen was calculated to be 34 at % which implies that the sample was in the mixed phase of dihydride and solid solution.