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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 1,225 records · Page 68
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Experimental and Theoretical Analyses of Zinc-Vacancy-Induced Room-Temperature Ferromagnetism in ZnO Films

Room-temperature ferromagnetism (RTFM) has been observed in RF magnetron sputtered ZnO films with O{sub 2} as an auxiliary gas after annealing. The films exhibit hexagonal wurtzite structure and observable ferromagnetism. A maximum of saturation magnetization of 4.75 emu/cm{sup 3} is obtained. The zinc vacancies are believed as the RTFM origin, and oxygen vacancies are not an incentive of magnetization of the ZnO films. Theoretical study based on first principles calculation is performed for better understanding of the RTFM in substance. The intrinsic physical mechanism of regulating the ferromagnetic of the ZnO film is analyzed in detail.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2011

Room-temperature optical absorption in the InAs/GaAs quantum-dot superlattice under an electric field

Electroluminescence and absorption spectra of a ten-layer InAs/GaAs quantum dot (QD) superlattice built in a two-section laser with sections of equal length is experimentally studied at room temperature. The thickness of the GaAs spacer layer between InAs QD layers, determined by transmission electron microscopy, is {approx}6 nm. In contrast to tunnel-coupled QDs, QD superlattices amplify the optical polarization intensity and waveguide absorption of the TM mode in comparison with the TE mode. It is found that variations in the multimodal periodic spectrum of differential absorption of the QD superlattice structure are strongly linearly dependent on the applied electric field. Differential absorption spectra exhibit the Wannier-Stark effect in the InAs/GaAs QD superlattice, in which, in the presence of an external electric field, coupling of wave functions of miniband electron states is suppressed and a series of discrete levels called the Wannier-Stark ladder states are formed.

36 MATERIALS SCIENCE↗
DOE OSTI2011

Interfacial luminescence in an InAs/InAsSbP isotype type II heterojunction at room temperature

Interfacial luminescence on a single type II heterointerface in the InAs/InAsSbP system at room temperature is observed for the first time. It is confirmed experimentally that a single InAs/InAsSbP hetero-structure is a staggered type II heterojunction. The formation of an electron channel at the heterointerface on the n-InAs side in the n-InAs/n-InAsSbP heterostructure does not lead to the emergence of the radiative interfacial luminescence, while the p-InAs/p-InAsSbP heterostructure under the reverse bias manifests the interfacial luminescence caused by radiative transitions of holes from the occupied surface states localized at the heterointerface. The discovery of an intense interfacial luminescence comparable with bulk luminescence in intensity opens novel opportunities for the design of multicolor light-emitting diodes and integrated opto-electronic matrices for the mid-IR range of 3-5 {mu}m.

36 MATERIALS SCIENCE↗
DOE OSTI2013

The analysis of leakage current in MIS Au/SiO{sub 2}/n-GaAs at room temperature

The aim of this study is to determine the reverse-bias leakage current conduction mechanisms in Au/SiO{sub 2}/n-GaAs metal-insulator-semiconductor type Schottky contacts. Reverse-bias current-voltage measurements (I–V) were performed at room temperature. The using of leakage current values in SiO{sub 2} at electric fields of 1.46–3.53 MV/cm, ln(J/E) vs. <##> } E $ /sqrt E $ √E </##> graph showed good linearity. Rom this plot, dielectric constant of SiO{sub 2} was calculated as 3.7 and this value is perfect agreement with 3.9 which is value of SiO{sub 2} dielectric constant. This indicates, Poole-Frenkel type emission mechanism is dominant in this field region. On the other hand, electric fields between 0.06–0.73 and 0.79–1.45 MV/cm, dominant leakage current mechanisms were found as ohmic type conduction and space charge limited conduction, respectively.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Room-temperature lasing in microring cavities with an InAs/InGaAs quantum-dot active region

Microring cavities (diameter D = 2.7-7 {mu}m) with an active region based on InAs/InGaAs quantum dots are fabricated and their characteristics are studied by the microphotoluminescence method and near-field optical microscopy. A value of 22 000 is obtained for the Q factor of a microring cavity with the diameter D = 6 {mu}m. Lasing up to room temperature is obtained in an optically pumped ring microlaser with a diameter of D = 2.7 {mu}m.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Room temperature de Haas–van Alphen effect in silicon nanosandwiches

The negative-U impurity stripes confining the edge channels of semiconductor quantum wells are shown to allow the effective cooling inside in the process of the spin-dependent transport. The aforesaid also promotes the creation of composite bosons and fermions by the capture of single magnetic flux quanta at the edge channels under the conditions of low sheet density of carriers, thus opening new opportunities for the registration of quantum kinetic phenomena in weak magnetic fields at high temperatures up to the room temperature. As a certain version noted above, we present the first findings of the high temperature de Haas–van Alphen (300 K) and quantum Hall (77 K) effects in the silicon sandwich structure that represents the ultranarrow, 2 nm, p-type quantum well (Si-QW) confined by the delta barriers heavily doped with boron on the n-type Si (100) surface. These data appear to result from the low density of single holes that are of small effective mass in the edge channels of p-type Si-QW because of the impurity confinement by the stripes consisting of the negative-U dipole boron centers which seems to give rise to the efficiency reduction of the electron–electron interaction.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Room-temperature operation of quantum cascade lasers at a wavelength of 5.8 μm

The room-temperature generation of multiperiod quantum-cascade lasers (QCL) at a wavelength of 5.8 μm in the pulsed mode is demonstrated. The heterostructure of a quantum-cascade laser based on a heterojunction of InGaAs/InAlAs alloys is grown by molecular-beam epitaxy and incorporates 60 identical cascades. The threshold current density of the stripe laser 1.4 mm long and 22 μm wide is ~4.8 kA/cm{sup 2} at a temperature of 303 K. The maximum power of the optical-radiation output from one QCL face, recorded by a detector, is 88 mW. The actual optical-power output from one QCL face is no less than 150 mW. The results obtained and possible ways of optimizing the structure of the developed quantum-cascade lasers are discussed.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Room Temperature Lasing of Multi-Stage Quantum-Cascade Lasers at 8 μm Wavelength

Room-temperature lasing at a wavelength of 8 μm in multistage quantum-cascade lasers pumped by current pulses is demonstrated. A quantum-cascade laser heterostructure based on the In{sub 0.53}Ga{sub 0.47}As/A{sub l0.48}In{sub 0.5}2As alloy heteropair, matched to an InP substrate, is grown by molecular-beam epitaxy and consists of 50 identical cascades placed in a waveguide with air as the top cladding. A threshold current density of ~5.1 kA/cm{sup 2} at a temperature of 300 K is obtained in ridge lasers with a cavity length of 1.4 mm and a ridge width of 24 μm.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Effect of Nickel and Copper Introduced at Room Temperature on the Recombination Properties of Extended Defects in Silicon

The change in the recombination properties of individual dislocations and dislocation trails in silicon due to the diffusion of nickel and copper during chemical-mechanical polishing at room temperature is studied by the electron-beam- and light-beam-induced current techniques. It is found that the introduction of nickel results in an increase in the recombination activity of both dislocations and dislocation trails. The introduction of copper does not induce any substantial change in the contrast of extended defects.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Single-phase epitaxial InFeSb layers with a Curie temperature above room temperature

Epitaxial InFeSb/GaAs heterostructures were obtained by laser deposition in vacuum. Investigations by high-resolution transmission electron microscopy and microdiffraction showed that the InFeSb layers are single-crystal and do not contain additional phase inclusions. Study of their magnetotransport properties have revealed that an anomalous Hall effect and a negative magnetoresistance up to room temperature are observed in the structures.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Semiconductor Behavior and Room Temperature Ferromagnetism in e-Beam Evaporated Co/TiO{sub 2} Multilayer Thin Films

The Co/TiO{sub 2} multilayer thin films have been deposited by e-beam evaporation method on glass substrates in vacuum and annealed in air at 773 K for 1 h. The crystal structure, surface morphology, optical properties, electrical properties and magnetic properties of Co/TiO{sub 2} multilayer thin films have been systematically investigated. The results showed that the particle sizes were significantly reduced when the samples are annealed and the enlargement of particle size occurred when the samples thickness is increased. The spectroscopic analysis exhibited enhanced transmittance and higher optical band gap of annealed sample than the as-deposited one and it was decreased with sample thickness. The resistivity measurement confirmed resistivity decreament with temperature. Furthermore, by investigating the magnetic properties, room temperature ferromagnetism was observed.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Turn-on Dynamics of Quantum Cascade Lasers with a Wavelength of 8100 nm at Room Temperature

Lasing of quantum cascade lasers is demonstrated at a radiation wavelength of 8100 nm at room temperature. Analysis of oscillograms of optical pulses is used to determine dependence of mean and peak radiation intensities on current. A delay of turn-on of quantum cascade lasers is experimentally estimated at a level of two times higher than the lasing threshold to be greater than theoretically estimated delay by several orders of magnitude.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

Quantum-Cascade Lasers Generating at the 4.8-μm Wavelength at Room Temperature

We report on room-temperature generation at the 4.8-μm wavelength in a lattice-matched structure of a quantum cascade laser (QCL) grown on indium phosphide (InP) substrate. Laser heterostructures grown by molecular beam epitaxy (MBE) comprised 30 cascades and were designed to generate at the 4.80 μm wavelength corresponding to an atmospheric transparency window. Experiments demonstrated effective lasing at temperatures from 80 to 300 K on a wavelength coinciding with the calculated value, which confirmed the high quality of interfaces, high precision of layer thicknesses, and high accuracy of active region doping.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Room Temperature Lasing of Single-Mode Arched-Cavity Quantum-Cascade Lasers

Single-mode lasing at room temperature in quantum-cascade lasers (QCLs) with arched cavity design has been demonstrated. The output optical power in single-mode lasing regime at ~7.7-μm lasing wavelength was above 6 mW with a side-mode suppression ratio of up to 25 dB. The QCL heterostructure for the arched cavities was grown by molecular-beam epitaxy (MBE) based on a heterojunction of In{sub 0.53}Ga{sub 0.47}As/Al{sub 0.48}In{sub 0.52}As solid alloys, lattice-matched with InP substrate, and InP layers performing the function of waveguide claddings.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2026

Plasticizer-Free Gradient-Crosslinked Polyurethane Electrolyte for Room-Temperature Solid-State Lithium Batteries

Polymer-based solid-state electrolytes are promising for next-generation lithium metal batteries, yet their limited ionic conductivity and mechanical stability at ambient conditions remain key challenges. Herein, we report a novel gradient crosslinked polymer electrolyte (PU/PUA/PU) synthesized via a sequential in situ UV-curing process that integrates a mechanically robust polyurethane acrylate (PUA) core with soft linear polyurethane (PU) interfaces. This all-solid membrane operates without any liquid plasticizer and the interfacial PU layers ensure low interfacial resistance and intimate electrode contact, while the PUA core provides enhanced dimensional stability and dendrite suppression. As a result, the gradient electrolyte delivers an impressive ∼2.6 × 10 −4 S cm −1 ionic conductivity at 25 °C (two orders of magnitude higher than conventional PEO) and remains electrochemically stable >5 V (vs Li + /Li). Structural analysis confirms the formation of a well-defined crosslinked network with suppressed crystallinity and expanded interchain spacing. Electrochemical impedance spectroscopy (EIS) and linear sweep voltammetry (LSV) further validate these properties. When applied in a Li||NMC811 cell, the PU/PUA/PU electrolyte delivers stable cycling with high capacity at both 60 °C and 25 °C, demonstrating its potential for room-temperature solid-state battery applications without reliance on plasticizers or heating. In conclusion, this gradient design offers a practical path toward ambient-condition operation of solid-state lithium batteries, providing a paradigm for overcoming the traditional trade-off between ionic conductivity and mechanical robustness.

25 ENERGY STORAGE↗
DOE OSTI2019

220 Rn (Thoron) Geohazard in Room Air of Earthen Dwellings in Vietnam

Thoron’s ( 220 Rn) contribution to α -radiation exposure is usually considered negligible compared to that of 222 Rn (radon). Despite its short half-life of 55.6 seconds, thoron can be exhaled from porous surface layers of building materials into indoor air where people subsequently inhale radioisotopes, including metallic radioactive progeny. Bare surfaces of dry porous soil with relatively high 232 Th content can pose a thoron radiation hazard in indoor air. On northern Vietnam’s Dong Van karst plateau, the spatial distribution of thoron was determined in indoor air of traditional earthen and other types of dwellings using portable RAD7 and SARAD® RTM 2200 detectors. “Mud houses” are constructed with local compacted soil and typically do not have any floor or wall coverings (i.e., no plaster, wallpaper, or paint). Detailed measurements in a mud house revealed levels of thoron in room air averaging >500 Bq m -3 . The spatial distribution of α -radiation from thoron in indoor air at a distance of about 1 m from interior walls was fairly homogeneous and averaged ~200 Bq m -3 . Most concerning, from a human health perspective, were the high thoron concentrations of up to 884 Bq m -3 in sleeping areas near mud walls. The average annual thoron radiation dose to inhabitants of mud houses was estimated based on 13 hours of daily occupancy, including daily activities and sleeping. The estimated average thoron inhalation dose of 27.1 mSv a -1 during sleeping hours near mud surfaces accounts for nearly 75% of the total estimated radon and thoron inhalation dose of 37.4 mSv a -1 from indoor mud house air. Our conservative annual radiation dose estimates do not include subsequent radiation from inhaled metallic progeny of thoron. Our data demonstrate a significant human health risk from radiation exposure and a critical need for remediation in traditional northern Vietnamese mud house dwellings.

58 GEOSCIENCES↗