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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 73 records · Page 4
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NASA NTRS1987

Photoemission studies of core level shifts in HgCdTe, CdMnTe, and HgZnTe

The results of photoemission studies of core level shifts in the Hg(1-x)Cd(x)Te, Cd(1-x)Mn(x)Te, and Hg(1-x)Zn(x)Te alloys are discussed. In Hg(0.7)Cd(0.3)Te, the Hg 5d level is found to shift to lower binding energy by 0.1 eV, and the Cd 4d level to shift to higher binding energy by 0.25 eV upon alloying (relative to their binaries). The Born-Haber cycle is used to determine core level binding energies relative to the valence-band maximum in the context of tight-binding theory, and calculated core level shifts upon alloying in HgCdTe are shown to be too small to account for the observed values. A natural valence-band offset between HgTe and CdTe of 0.35 eV is found.

Shih, C. K.↗
NASA NTRS1990

Infrared response from metallic particles embedded in a single-crystal Si matrix - The layered internal photoemission sensor

Infrared radiation at wavelengths of 1-2 microns has been detected in a new device labeled the layered internal photoemission sensor. The device structure, which is grown by molecular beam epitaxy, incorporates epitaxial CoSi2 particles with dimensions of 10-50 nm. Radiation absorbed by these particles photoexcites carriers into a surrounding single-crystal silicon matrix. A peak quantum efficiency of 1.3 percent is measured, which is approximately six times higher than in planar CoSi2 Schottky diodes with 5-nm silicide thickness.

Fathauer, R. W.↗
NASA NTRS1990

Novel Si(1-x)Ge(x)/Si heterojunction internal photoemission long-wavelength infrared detectors

The feasibility of a novel p(+)-Si(1-x)Ge(x)-p-Si heterojunction internal photoemission (HIP) IR detector is demonstrated. A degenerately doped p(x)-Si(1-x)Ge(x) layer is required for strong IR absorption to generate photoexcited holes. The Si(1-x)Ge(x) layers are grown by molecular beam epitaxy, with boron concentrations up to 10 to the 20th/cu cm achieved by using an HBO2 source. Photoresponse at wavelengths ranging from 2 to 10 microns has been obtained with quantum efficiencies above 1 percent. The tailorable cutoff wavelength of the HIP detector has been demonstrated by varying the Ge composition ratio in the Si(1-x)Ge(x) layers.

Lin, T. L.↗
NASA NTRS1991

Heterojunction-Internal-Photoemission Infrared Detectors

New type of photodetector adds options for design of imaging devices. Heterojunction-internal-photoemission (HIP) infrared photodetectors proposed for incorporation into planar arrays in imaging devices required to function well at wavelengths from 8 to 17 micrometers and at temperatures above 65 K. Photoexcited electrons cross energy barrier at heterojunction and swept toward collection layer. Array of such detectors made by etching mesa structures. HIP layers stacked to increase quantum efficiency. Also built into integrated circuits including silicon multiplexer/readout circuits.

Maserjian, Joseph↗
NASA NTRS1990

Photovoltaic effects in photoemission studies of Schottky barrier formation

It is shown here that much of the recent photoelectron spectroscopy literature describing the onset of pinning in adsorbate-semiconductor systems at low temperature must be reinterpreted in light of surface photovoltaic effects. Two sources of surface charging are discussed, both of which are strongly enhanced at low temperature. The surface photovoltage resulting from separation of electron-hole pairs by the electric field in the depletion region is usually the dominant source of surface potential shifts, and causes flattening of the semiconductor bands. In addition, surface charging due to photoemission into the vacuum may reverse bias a p-type diode at low temperatures, causing increase band bending.

Hecht, M. H.↗
NASA NTRS1990

An imaging photoemission polarimeter for soft X-rays

Results of investigations are reviewed to assess the polarization dependence of photoemission in the optical, UV, and soft X-ray bands, as well as present a design for an imaging photoelectric polarimeter. Data regarding the effect of the dependence in the soft X-ray band are emphasized including the quantity of photons produced by each X-ray. The phase shift encountered in some experiments indicates that a third axis is present; the importance of the phase shift in understanding the vectoral photoeffect is emphasized. Measurements of the pulse height show that this measure is proportional to the number of electrons photoemitted by the incident X-ray. The development of X-ray polarimeters can be significantly improved as a result of the study of polarization sensitivity in the photoelectric effect. The design of a photoelectric polarimeter is presented, and the potential uses for the instrument include measuring the polarization of supernova remnants, AGN, and black hole candidates.

Kaaret, Philip↗
NASA NTRS1995

Unoccupied electronic resonances of Sc adsorbed on W(001) by k-resolved inverse photoemission

Scandium adsorbed on the (001) face of tungsten has been studied using Auger-electron spectroscopy, low-energy electron diffraction, k-resolved inverse photoelectron spectroscopy, work-function measurements, and relativistic-electronic-structure calculations. We find that the work function of W(001) does not decrease monotonically as a function of scandium adsorption but reaches a minimum value of Phi = 3.25 eV at 50% coverage. For a complete monolayer, an order 1 X 1 Sc overlayer is formed. Inverse photoemission in the isochromat mode was used to map the unoccupied energy levels of this overlayer along the bar-Gamma(bar-Mu) symmetry direction of the surface Brillouin zone. Local-density-functional calculations using the muffin-tin orbital method were performed for a 1 X 1 Sc overlayer on W and are compared with the experimental two-dimensional band structure.

Lamouri, A.↗
NASA NTRS1996

X-Ray Photoemission Measurements of La(1-x)Ca(x)CoO3(x = 0, 0.5)

X-ray photoemission measurements of the core levels and valence electronic structure of LaCoO3 and La(0.5)Ca(0.5)CoO3 high quality epitaxial films are presented. Shifts of the core levels and main valence band features are consistent with a doping-induced change in the chemical potential. Oxygen states are found to significantly contribute to a peak in the valence band at 1 eV binding energy, verifying earlier results of cluster calculations. A Fermi level crossing of this same band upon doping is observed, yielding a high Fermi level density of states.

Vasquez, R. P.↗
NASA NTRS1995

X-Ray Photoemission Measurements and Electronic Structure of HgBa2CaCu2O6+Delta

X-ray photoelectron spectroscopy data presented here are the first on an epitaxial thin film of a mercury cuprate superconductor, the first in which signals from the superconducting phase dominate all the core level spectra, and the first to exhibit a clear Fermi edge in the valence band region. Mercury is found to be in a single chemical state, contrary to reports based on sintered polycrystalline pellets.

x-ray photoemission photoelectron spectroscopy mer↗