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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 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS2005

Composition-Temperature-Partial Pressures Data for Cd(sub 0.8)Zn(sub 0.2)Te by Optical Absorption Measurements

Known weights of Cd, Zn and Te were reacted in silica optical cells of known volume and the partial pressure of Te2 and Zn between 485 and 1160 C were determined by measuring the optical density of the vapor in the ultra-violet to visible range. The composition of the condensed phase or phases was calculated from the original weights and the amount of material in the vapor phase. The corresponding composition - temperature - partial pressures, x(sub Te)-T-P(sub Te2), data, including five Te-rich solidus points, were established. The solubility range for the Te-rich Cd(sub 0.8)Zn(sub 0.2)Te(s) is similar to that of CdTe(s) with x(sub Te) = 0.50005 at 809 C and an estimated maximum solubility of x(sub Te) = 0.50012 at about 1000 C. The partial pressure of Cd and Te(sub 2) measured over the Cd(sub 0.8)Zn(sub 0.2)Te melt at 1140 C were about 1.55 and 0.02 atm, respectively, and the corresponding P(Sub Zn) was estimated to be 0.05 atm. It was recommended that a Cd reservoir maintaining at 800 to 820 C should be used during directional solidification of Cd(sub o.8)Zn(sub 0.2)Te to prevent the preferential loss of Cd to the vapor phase.

Su, Ching-Hua↗
DOE OSTI2021

Apparatus and method to measure semiconductor optical absorption using microwave charge sensing

A time-resolved microwave reflectance apparatus comprises a pulsed or modulated optical source that irradiates a semiconductor sample with an excitation pump beam, a microwave oscillator that irradiates the sample with a continuous beam of microwaves, and a microwave detector that detects the microwaves reflected by the sample. Therefore, charge detection, rather than conventional absorption measurements (that detect the loss of photons), can be used to extract the absorption coefficient and band edge of a semiconductor material.

Shaner, Eric A.↗
DOE OSTI2025

Setup for Optical Absorption Measurements of Molten Salt Mixtures

In this work we describe the setup of a spectrophotometer to take absorbance measurements of a heated sample in an inert atmosphere. By using fiber optics to bring light into and out of a glovebox we are able to use a pitch-catch optical setup to observe samples in a cuvette heated up to 400℃. The functionality of the setup is demonstrated by observing the signal produced by Li 2 S in a eutectic mixture of LiCl/LiBr/KBr at elevated temperature overtime.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Introduction of localized spin-state transitions in the optical absorption spectrum of Cr-doped GaN

Using a hybrid density functional, we study the electronic, magnetic, and neutral excitations of the paradigmatic Cr-doped GaN solid. Our results indicate that the ≈1% doped wurtzite GaN crystal retains the semiconducting nature of the host, associated with a magnetic moment of 3 μ B . Further, as a consequence of Cr doping, additional hybridized bands are formed within the intrinsic band gap of GaN, leading to a considerable band gap narrowing by 1.4 eV and low-energy optical transitions. Our results indicate dark Cr d-d transitions at very low energy (0.5–0.7 eV), followed by bright transitions in the visible energy range (1.8–2.2 eV). Characterization of the electron-hole pairs suggests that the latter originates from the internal transitions among hybridized Cr d –N p states. With the existence of these additional optical features within the visible energy window, one can expect an enhancement to the photoelectric conversion efficiency of GaN upon Cr doping, in addition to applications in spintronics.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Optical absorption of interlayer excitons in transition-metal dichalcogenide heterostructures

Interlayer excitons, electron-hole pairs bound across two monolayer van der Waals semiconductors, offer promising electrical tunability and localizability. Because such excitons display weak electron-hole overlap, most studies have examined only the lowest-energy excitons through photoluminescence. Here, we directly measured the dielectric response of interlayer excitons, which we accessed using their static electric dipole moment. We thereby determined an intrinsic radiative lifetime of 0.40 nanoseconds for the lowest direct-gap interlayer exciton in a tungsten diselenide/molybdenum diselenide heterostructure. We found that differences in electric field and twist angle induced trends in exciton transition strengths and energies, which could be related to wave function overlap, moiré confinement, and atomic reconstruction. Through comparison with photoluminescence spectra, this study identifies a momentum-indirect emission mechanism. Characterization of the absorption is key for applications relying on light-matter interactions.

42 ENGINEERING↗