Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “ROOM”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,747 records · Page 97
All sourcesNASA NTRSDOE OSTI
DOE OSTI2012

Liquid metal alloy ion source based metal ion injection into a room-temperature electron beam ion source

We have carried out a series of measurements demonstrating the feasibility of using the Dresden electron beam ion source (EBIS)-A, a table-top sized, permanent magnet technology based electron beam ion source, as a charge breeder. Low charged gold ions from an AuGe liquid metal alloy ion source were injected into the EBIS and re-extracted as highly charged ions, thereby producing charge states as high as Au{sup 60+}. The setup, the charge breeding technique, breeding efficiencies as well as acceptance and emittance studies are presented.

43 PARTICLE ACCELERATORS↗
DOE OSTI2013

Room temperature synthesis of Mn{sup 2+} doped ZnS d-dots and observation of tunable dual emission: Effects of doping concentration, temperature, and ultraviolet light illumination

Mn{sup 2+} doped (0-50.0 molar %) ZnS d-dots have been synthesized in water medium by using an environment friendly low cost chemical technique. Tunable dual emission in UV and yellow-orange regions is achieved by tailoring the Mn{sup 2+} doping concentration in the host ZnS nanocrystal. The optimum doping concentration for achieving efficient photoluminescence (PL) emission is determined to be {approx}1.10 (at. %) corresponding to 40.0 (molar %) of Mn{sup 2+} doping concentration used during synthesis. The mechanism of charge transfer from the host to the dopant leading to the intensity modulated tunable (594-610 nm) yellow-orange PL emission is straightforwardly understood as no capping agent is used. The temperature dependent PL emission measurements are carried out, viz., in 1.10 at. % Mn{sup 2+} doped sample and the experimental results are explained by using a theoretical PL emission model. It is found that the ratio of non-radiative to radiative recombination rates is temperature dependent and this phenomenon has not been reported, so far, in Mn{sup 2+} doped ZnS system. The colour tuning of the emitted light from the samples are evident from the calculated chromaticity coordinates. UV light irradiation for 150 min in 40.0 (molar %) Mn{sup 2+} doped sample shows an enhancement of 33% in PL emission intensity.

36 MATERIALS SCIENCE↗
DOE OSTI2014

A room temperature electron cyclotron resonance ion source for the DC-110 cyclotron

The project of the DC-110 cyclotron facility to provide applied research in the nanotechnologies (track pore membranes, surface modification of materials, etc.) has been designed by the Flerov Laboratory of Nuclear Reactions of the Joint Institute for Nuclear Research (Dubna). The facility includes the isochronous cyclotron DC-110 for accelerating the intensive Ar, Kr, Xe ion beams with 2.5 MeV/nucleon fixed energy. The cyclotron is equipped with system of axial injection and ECR ion source DECRIS-5, operating at the frequency of 18 GHz. This article reviews the design and construction of DECRIS-5 ion source along with some initial commissioning results.

43 PARTICLE ACCELERATORS↗
DOE OSTI2013

Room temperature in-plane 〈100〉 magnetic easy axis for Fe{sub 3}O{sub 4}/SrTiO{sub 3}(001):Nb grown by infrared pulsed laser deposition

We examine the magnetic easy-axis directions of stoichiometric magnetite films grown on SrTiO{sub 3}:Nb by infrared pulsed-laser deposition. Spin-polarized low-energy electron microscopy reveals that the individual magnetic domains are magnetized along the in-plane 〈100〉 film directions. Magneto-optical Kerr effect measurements show that the maxima of the remanence and coercivity are also along in-plane 〈100〉 film directions. This easy-axis orientation differs from bulk magnetite and films prepared by other techniques, establishing that the magnetic anisotropy can be tuned by film growth.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Spin reorientation transition and near room-temperature multiferroic properties in a W-type hexaferrite SrZn{sub 1.15}Co{sub 0.85}Fe{sub 16}O{sub 27}

In this Letter, we investigate the magnetic and multiferroic properties of a W-type hexaferrite SrZn{sub 1.15}Co{sub 0.85}Fe{sub 16}O{sub 27}. Due to the strong planar contribution to the anisotropy provided by Co{sup 2+} ions, this hexaferrite shows a spin reorientation transition from easy-axis to easy-cone at 302 K, which is different from the onset temperature of ferroelectric polarization, 275 K. By applying magnetic field, a remarkable drop of polarization is observed, suggesting a large magnetoelectric effect in this multiferroics. The difference between spin reorientation and ferroelectric phase transition temperature as well as the origin of magnetoelectric effect are discussed.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Near fifty percent sodium substituted lanthanum manganites—A potential magnetic refrigerant for room temperature applications

Nearly half of lanthanum sites in lanthanum manganites were substituted with monovalent ion-sodium and the compound possessed distorted orthorhombic structure. Ferromagnetic ordering at 300 K and the magnetic isotherms at different temperature ranges were analyzed for estimating magnetic entropy variation. Magnetic entropy change of 1.5 J·kg{sup −1}·K{sup −1} was observed near 300 K. An appreciable magnetocaloric effect was also observed for a wide range of temperatures near 300 K for small magnetic field variation. Heat capacity was measured for temperatures lower than 300 K and the adiabatic temperature change increases with increase in temperature with a maximum of 0.62 K at 280 K.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Enhanced room temperature magnetoresistance in p−La{sub 0.7}Ca{sub 0.3}MnO{sub 3}/SrTiO{sub 3}/n−Si heterostructure: A possible spintronics application

An experimental study of p−La{sub 0.7}Ca{sub 0.3}MnO{sub 3}/SrTiO{sub 3}/n−Si heterostructure in which La{sub 0.7}Ca{sub 0.3}MnO{sub 3} (LCMO) and Si are separated by a thin interfacial SrTiO{sub 3} (STO) layer with typical thickness ∼ 15 nm, has been in situ fabricated with the pulsed laser deposition technique. The junction exhibits good rectifying diode like behavior over the temperature range of 10 - 300 K. The heterostructure also exhibits metal-oxide-semiconductor like behavior with all type of possible current flow mechanisms through the heterojunction. The junction magnetoresistance (JMR) (∼ 30% at 300 K) properties of p-LCMO/STO/n-Si heterostructure have been studied over the temperature range of 100-300 K. The JMR is positive and strongly depends on temperature at an applied forward bias voltage of 3 V. The relation between JMR and external magnetic field is found to be Δρ/ρ≈ α H{sup β} type, having both α and β temperature dependent. We attribute the emergence of positive JMR to the quantum mechanical tunneling transport mechanism across the heterojunction.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Electric field effects on spin accumulation in Nb-doped SrTiO{sub 3} using tunable spin injection contacts at room temperature

We report on features in charge transport and spin injection in an oxide semiconductor, Nb-doped SrTiO{sub 3}. This is demonstrated using electrically tunable spin injection contacts which exploit the large electric field at the interface and its interplay with the relative permittivity of the semiconductor. We realize spin accumulation in Nb-doped SrTiO{sub 3} which displays a unique dependence of the spin lifetime with bias polarity. These findings suggest a strong influence of the interface electric field on the charge transport as well as on spin accumulation unlike in conventional semiconductors and opens up promising avenues in oxide spintronics.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

On the room-temperature phase diagram of high pressure hydrogen: An ab initio molecular dynamics perspective and a diffusion Monte Carlo study

The finite-temperature phase diagram of hydrogen in the region of phase IV and its neighborhood was studied using the ab initio molecular dynamics (MD) and the ab initio path-integral molecular dynamics (PIMD). The electronic structures were analyzed using the density-functional theory (DFT), the random-phase approximation, and the diffusion Monte Carlo (DMC) methods. Taking the state-of-the-art DMC results as benchmark, comparisons of the energy differences between structures generated from the MD and PIMD simulations, with molecular and dissociated hydrogens, respectively, in the weak molecular layers of phase IV, indicate that standard functionals in DFT tend to underestimate the dissociation barrier of the weak molecular layers in this mixed phase. Because of this underestimation, inclusion of the quantum nuclear effects (QNEs) in PIMD using electronic structures generated with these functionals leads to artificially dissociated hydrogen layers in phase IV and an error compensation between the neglect of QNEs and the deficiencies of these functionals in standard ab initio MD simulations exists. This analysis partly rationalizes why earlier ab initio MD simulations complement so well the experimental observations. The temperature and pressure dependencies for the stability of phase IV were also studied in the end and compared with earlier results.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Narrow-band single photon emission at room temperature based on a single nitrogen-vacancy center coupled to an all-fiber-cavity

We report the realization of a device based on a single Nitrogen-Vacancy (NV) center in diamond coupled to a fiber-cavity for use as single photon source (SPS). The device consists of two concave mirrors each directly fabricated on the facets of two optical fibers and a preselected nanodiamond containing a single NV center deposited onto one of these mirrors. Both, cavity in- and out-put are directly fiber-coupled, and the emission wavelength is easily tunable by variation of the separation of the two mirrors with a piezo-electric crystal. By coupling to the cavity, we achieve an increase of the spectral photon rate density by two orders of magnitude compared to free-space emission of the NV center. With this work, we establish a simple all-fiber based SPS with promising prospects for the integration into photonic quantum networks.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Room temperature magnetocaloric effect and refrigerant capacitance in La{sub 0.7}Sr{sub 0.3}MnO{sub 3} nanotube arrays

High aspect ratio La{sub 0.7}Sr{sub 0.3}MnO{sub 3} nanotube (NT) arrays have been synthesized using nitrates based sol-gel precursor by nanoporous anodized aluminum oxide template assisted method. Their phase purity and microstructures were analyzed by X-ray diffraction, scanning electron microscopy, and energy-dispersive x-ray spectroscopy. Magnetocaloric effect (MCE) of as prepared NTs was investigated by means of field dependence magnetization measurements. Significant magnetic entropy change, −△S{sub M} = 1.6 J/kg K, and the refrigerant capacitance, RC = 69 J/kg, were achieved near the transition temperature at 315 K for 5 T. For comparison, a bulk sample was also prepared using the same precursor solution which gives a value of −△S{sub M} = 4.2 J/kg K and a RC = 165 J/kg. Though the bulk sample exhibits higher △S{sub M} value, the NTs present an expanded temperature dependence of −△S{sub M} curves that spread over a broad temperature range and assured to be appropriate for active magnetic refrigeration. The diminutive MCE observed in manganite NTs is explained by the increased influence of surface sites of nanograins which affect the structural phase transition occurred by external magnetic field due to the coupling between magnetism and the lattice in manganese perovskites. Our report paves the way for further investigation in 1D manganite nanostructured materials towards applications in such magnetic refrigeration technology or even on hyperthermia/drug delivery.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2014

Metalized T graphene: A reversible hydrogen storage material at room temperature

Lithium (Li)-decorated graphene is a promising hydrogen storage medium due to its high capacity. However, homogeneous mono-layer coating graphene with lithium atoms is metastable and the lithium atoms would cluster on the surface, resulting in the poor reversibility. Using van der Waals-corrected density functional theory, we demonstrated that lithium atoms can be homogeneously dispersed on T graphene due to a nonuniform charge distribution in T graphene and strong hybridizations between the C-2p and Li-2p orbitals. Thus, Li atoms are not likely to form clusters, indicating a good reversible hydrogen storage. Both the polarization mechanism and the orbital hybridizations contribute to the adsorption of hydrogen molecules (storage capacity of 7.7 wt. %) with an optimal adsorption energy of 0.19 eV/H₂. The adsorption/desorption of H₂ at ambient temperature and pressure is also discussed. Our results can serve as a guide in the design of new hydrogen storage materials based on non-hexagonal graphenes.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2014

Nano-scale NiSi and n-type silicon based Schottky barrier diode as a near infra-red detector for room temperature operation

The fabrication of nano-scale NiSi/n-Si Schottky barrier diode by rapid thermal annealing process is reported. The characterization of the nano-scale NiSi film was performed using Micro-Raman Spectroscopy and X-ray Photoelectron Spectroscopy (XPS). The thickness of the film (27 nm) has been measured by cross-sectional Secondary Electron Microscopy and XPS based depth profile method. Current–voltage (I–V) characteristics show an excellent rectification ratio (I{sub ON}/I{sub OFF} = 10⁵) at a bias voltage of ±1 V. The diode ideality factor is 1.28. The barrier height was also determined independently based on I–V (0.62 eV) and high frequency capacitance–voltage technique (0.76 eV), and the correlation between them has explained. The diode photo-response was measured in the range of 1.35–2.5 μm under different reverse bias conditions (0.0–1.0 V). The response is observed to increase with increasing reverse bias. From the photo-responsivity study, the zero bias barrier height was determined to be 0.54 eV.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Thermal plasma processed ferro-magnetically ordered face-centered cubic iron at room temperature

Here, we report tailor made phase of iron nanoparticles using homogeneous gas phase condensation process via thermal plasma route. It was observed that crystal lattice of nano-crystalline iron changes as a function of operating parameters of the plasma reactor. In the present investigation iron nanoparticles have been synthesized in presence of argon at operating pressures of 125–1000 Torr and fixed plasma input DC power of 6 kW. It was possible to obtain pure fcc, pure bcc as well as the mixed phases for iron nanoparticles in powder form as a function of operating pressure. The as synthesized product was characterized for understanding the structural and magnetic properties by using X-ray diffraction, vibrating sample magnetometer, and Mössbauer spectroscopy. The data reveal that fcc phase is ferromagnetically ordered with high spin state, which is unusual whereas bcc phase is found to be ferromagnetic as usual. Finally, the structural and magnetic properties are co-related.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Room temperature spin-polarizations of Mn-based antiferromagnetic nanoelectrodes

Antiferromagnets produce no stray field, and therefore, a tip electrode made of antiferromagnetic material has been considered to be the most suitable choice to measure such as magnetoresistance (MR) through single isolated magnetic nanoparticles, molecules, and ultrathin films. Spin polarizations (P) of antiferromagnetic 3-nm, 6-nm, and annealed 3-nm Mn films grown on W tips with a bcc(110) apex as well as bulk-NiMn tips were obtained at 300 K by measuring MR in ultrahigh vacuum by means of spin-polarized scanning tunneling microscopy using a layerwise antiferromagnetically stacking bct-Mn(001) film electrode. The Mn-coated tips with coverages of 3 and 6 nm exhibited P values of 1 ± 1% and 3 ± 2%, respectively, which tips likely contain α- or strained Mn. With a thermal assist, the crystalline quality and the magnetic stability of the film could increase. The annealed tip exhibited P = 9 ± 2%. The bulk-NiMn tips exhibit spin polarizations of 0 or 6 ± 2% probably depending on the chemical species (Mn or Ni) present at the apex of the tip. Fe-coated W tips were used to estimate the bct-Mn(001) film spin polarization.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

High temperature electron spin dynamics in bulk cubic GaN: Nanosecond spin lifetimes far above room-temperature

The electron spin dynamics in n-doped bulk cubic GaN is investigated for very high temperatures from 293 K up to 500 K by time-resolved Kerr-rotation spectroscopy. We find extraordinarily long spin lifetimes exceeding 1 ns at 500 K. The temperature dependence of the spin relaxation time is in qualitative agreement with predictions of Dyakonov-Perel theory, while the absolute experimental times are an order of magnitude shorter than predicted. Possible reasons for this discrepancy are discussed, including the role of phase mixtures of hexagonal and cubic GaN as well as the impact of localized carriers.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Long-wavelength shift and enhanced room temperature photoluminescence efficiency in GaAsSb/InGaAs/GaAs-based heterostructures emitting in the spectral range of 1.0–1.2 μm due to increased charge carrier's localization

In this work, a study of the photoluminescence (PL) temperature dependence in quantum well GaAs/GaAsSb and double quantum well InGaAs/GaAsSb/GaAs heterostructures grown by metalorganic chemical vapor deposition with different parameters of GaAsSb and InGaAs layers has been performed. It has been demonstrated that in double quantum well InGaAs/GaAsSb/GaAs heterostructures, a significant shift of the PL peak to a longer-wavelength region (up to 1.2 μm) and a considerable reduction in the PL thermal quenching in comparison with GaAs/GaAsSb structures can be obtained due to better localization of charge carriers in the double quantum well. For InGaAs/GaAsSb/GaAs heterostructures, an additional channel of radiative recombination with participation of the excited energy states in the quantum well, competing with the main ground-state radiative transition, has been revealed.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

The role of residual charges in the repeatability of the dynamics of atmospheric pressure room temperature plasma plume

To better understand the role of residual electrons in the repeatability of an atmospheric pressure plasma plume, the characteristics of a helium plasma jet from the 1st, 2nd,… until the repeatable discharge pulse are investigated for the first time. It's found that the longest plasma plume is achieved in the 1st discharge pulse. The length of the plasma plume becomes shorter and shorter and reaches a constant value in the 3rd discharge pulse and keeps the same for the following pulses. The dynamics of the 1st discharge pulse show that the plasma bullet appears random in nature. Two photomultiplier tubes are used to distinguish the two potential factors that could result in the stochastic dynamics of the plasma bullet, i.e., stochastic ignition of the plasma and the stochastic propagation velocity. The results show that the stochastic propagation velocity occurs only in the 1st and the 2nd discharge pulses, while the stochastic ignition of the plasma presents until the 100th pulse. The dynamics of the plasma propagation become repeatable after about 100 pulses. Detail analysis shows that the repeatability of plasma bullet is due to the residual electrons density. The residual electron density of 10{sup 9 }cm{sup −3} or higher is needed for repeatable discharges mode.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗