Infrared Absorption of U Centers in CsBr and CsI

Measurements were made of the absorption of the infrared-active local mode of H− and D− substitutional impurities in CsBr and CsI from 5 to about 100 K. In CsBr, the T2 dependence of the half-width above about 30 K indicates the local mode is broadened by the Raman or scattering mechanism, while the constant low-temperature half-widths are characteristic of the decay of the local mode into three (D−) or four (H−) lattice phonons. The sidebands are weak, and are described well by the model of Bilz, Fritz, and Strauch, in which the polarizability of the impurity is important. The resultant lattice density of states for CsBr is in good agreement with that calculated by Karo and Hardy using a model with the deformation dipoles on anions only. The main absorption peak in CsI was not Lorentzian, but no origin for the unresolved structure was found. The phonon density of states deduced from the sidebands in CsI agrees reasonably well with Karo and Hardy\u27s calculated curve

Reflectance spectra and dielectric functions for Ag in the region of interband transitions

New measurements have been made of the reflectances of single crystals of Ag and of Ag films in the (3.5-30)-eV range. The data were analyzed with the Kramers-Kronig method and the resultant dielectric functions were compared with those in the literature and with recent calculations. We find all structures previously seen, and a new weak peak at 11.5 eV. Our magnitudes for ε2 are in considerably better agreement with those of the calculated spectra than are those in the literature. Second-derivative spectra of the absorption coefficient have been calculated and compared with previously measured thermotransmission spectra, showing the latter to arise primarily by temperature-dependent broadening

Longitudinal-Optical-Phonon-Plasmon Coupling in GaAs

Infrared reflectivity measurements have been made at 78°K on three samples of GaAs, doped with Te so that the plasma frequency is nearly equal to the long-wavelength LO phonon frequency. There are two prominent dips in the reflectivity spectra, but instead of occurring near the plasma frequency and LO mode frequency, they occur at the frequencies of the two normal modes of the coupled plasmon-LO-phonon system, as predicted by Varga and by Singwi and Tosi. From the reflectivity spectra at 78°K, values of the electron effective mass of 0.067, 0.073, and 0.077me are obtained for n-type GaAs with 7.22×1017, 8.75×1017, and 14.0×1017 carriers per cm3

Photoemission study of Ce-catalyzed oxidation of W(110) and W(111)

Different catalytic oxidation effects of Ce on W(110) and W(111) were observed with photo- emission spectroscopy. On Ce-covered W(110), the top W layer is quickly oxidized to a surface monoxide at room temperature. Oxidation is almost halted after the completion of one monolayer of WO. On Ce/W(111), instead of WO, WO3 grows on the surface under the same conditions. The monolayer suboxide formation found on Ce/W(110) and Ce/Ta(110) (as reported earlier) is a direct consequence of the most densely packed structure of the bcc (110) surfaces. The more effective oxidation promotion on the W(111) surface is attributed to its open structure. The mechanism of Ce-catalyzed oxidation is further tested in this study

NASA space cell test program Progress report, period ending 31 Dec. 1968

Performance tests on separator materials for silver zinc batterie

NASA space cell test program Monthly progress report, 1-31 Dec. 1968

Status of spacecraft cell testing progra

Optical properties of single crystals of some rare-earth trifluorides, 5-34 eV

The reflectances of single crystals of the trifluorides of La, Ce, Pr, Nd, Dy, and of polycrystalline GdF3 were measured in the 10-34-eV region, along with 5-9-eV transmission measurements on films of these materials. Localized 4f→5d, 6stransitions on the rare-earth ions give rise to the absorption below 10 or 11 eV. Strong interband absorption gives anisotropic reflectance peaks in the 10-15-eV region, presumably from F− 2p valence bands to lanthanide 5d, 6s (and other states) conduction bands, accounting for about one-third of the expected F− 2p osillator strength. Transitions from lanthanide 5p levels cause two types of spectra beginning around 20 eV: transitions of the 5p→5d type, apparently localized on lanthanide ions, but with some an isotropy; and transitions of 5p electrons to the conduction band, giving a peak of very high reflectance at energies above 27 eV

High-resolution photoemission study of γ- and α-cerium

High-resolution photoemission studies on the α and γ phases of cerium show changes in the binding energies of the two4f-related features. The location of the two 4f-related features in the γ phase are at -0.2 and -2.0 eV, while in the αphase these features are located at the Fermi level and -2.1 eV. These results are a direct test of the theories proposed to explain the presence of the two features

Valence-Band Photoemission in La and Pr: Connections with the Ce Problem

Energy distribution curves from La and Pr were taken from 32 to 80 eV photon energies. Above 50 eV the valence-band photoemission in La is very weak, implying that previous studies of Ce have underemphasized the 4f contributions. Pr exhibits two peaks attributable to 4f electrons, similar to the structures in Ce