Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “impurity”

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 1,009 records · Page 56
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

Generation of spin-polarized currents via cross-relaxation with dynamically pumped paramagnetic impurities

Key to future spintronics and spin-based information processing technologies is the generation, manipulation, and detection of spin polarization in a solid state platform. Here, we theoretically explore an alternative route to spin injection via the use of dynamically polarized nitrogen-vacancy (NV) centers in diamond. We focus on the geometry where carriers and NV centers are confined to proximate, parallel layers and use a “trap-and-release” model to calculate the spin cross-relaxation probabilities between the charge carriers and neighboring NV centers. We identify near-unity regimes of carrier polarization depending on the NV spin state, applied magnetic field, and carrier g-factor. In particular, we find that unlike holes, electron spins are distinctively robust against spin-lattice relaxation by other, unpolarized paramagnetic centers. Further, the polarization process is only weakly dependent on the carrier hopping dynamics, which makes this approach potentially applicable over a broad range of temperatures.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Hydrogen passivation of titanium impurities in silicon: Effect of doping conditions

While the contamination of solar silicon by fast diffusing transition metals can be now limited through gettering, much attention has been drawn to the slow diffusing species, especially the early 3d and 4d elements. To some extent, hydrogen passivation has been successful in healing many deep centers, including transition metals in Si. Recent deep-level transient spectroscopy (DLTS) measurements concerning hydrogen passivation of Ti revealed the existence of at least four electrical levels related to Ti{sub i}H{sub n} in the upper-half of the gap. These findings challenge the existing models regarding both the current level assignment as well as the structure/species involved in the defects. We revisit this problem by means of density functional calculations and find that progressive hydrogenation of interstitial Ti is thermodynamically stable in intrinsic and n-doped Si. Full passivation may not be possible to attain in p-type Si as Ti{sub i}H{sub 3} and Ti{sub i}H{sub 4} are metastable against dissociation and release of bond-centered protons. All DLTS electron traps are assigned, namely, E40′ to Ti{sub i}H(-/0), E170′ to Ti{sub i}H{sub 3}(0/+), E(270) to Ti{sub i}H{sub 2}(0/+), and E170 to Ti{sub i}H(0/+) transitions. Ti{sub i}H{sub 4} is confirmed to be electrically inert.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Coaxial pellets for metallic impurity injection on the large helical device

Two coaxial pellets with tungsten inserted into graphite carbon and polyethylene (PE) tubes are compared for tungsten spectroscopic study in the Large Helical Device. The tungsten pellet with carbon tube causes plasma collapse, while that with PE tube smoothly ablates without collapse. The deposition profile of the pellets is analyzed with a help of pellet ablation spectroscopy. It is found that the tungsten pellet with carbon tube can significantly penetrate into the core plasma and leads to the plasma collapse. A tungsten spectrum with radial profile is successfully observed when the tungsten pellet with PE tube is used.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Low-temperature ordering caused by exchange interaction in the Si:P impurity system near the insulator - Metal phase transition

Behavior of the paramagnetic susceptibility in Si:P at low temperatures was investigated by Electron Spin Resonance in order to detect the antiferromagnetic and ferromagnetic ordering in the vicinity of the insulator-metal phase transition. A procedure was developed to operate sufficiently smooth changes of the spin density, by proton irradiated.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

Reduced electrical impedance of SiO{sub 2}, deposited through focused ion beam based systems, due to impurity percolation

The electrical impedance (both the resistive and capacitive aspects) of focused ion beam (FIB) deposited SiO{sub 2} has been correlated to the specific composition of the ion beam, in Ga- and Xe-based FIB systems. The presence of electrically percolating Ga in concert with carbon (inevitably found as the product of the hydrocarbon precursor decomposition) has been isolated as a major cause for the observed decrease in the resistivity of the deposited SiO{sub 2}. Concomitant with the decreased resistivity, an increased capacitance and effective dielectric constant was observed. Our study would be useful to understand the constraints to the deposition of high quality insulator films through FIB based methodologies.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Electric field induced optical gain of a hydrogenic impurity in a Cd{sub 0.8}Zn{sub 0.2}Se/ZnSe parabolic quantum dot

The dependence of electric field on the electronic and optical properties is investigated in a Cd{sub 0.8}Zn{sub 0.2}Se/ZnSe quantum dot. The hydrogenic binding energy, in the presence of electric field, is calculated with the spatial confinement effect. The electric field dependent optical gain with the photon energy is found using compact density matrix method. The results show that the electric field has a great influence on the optical properties of II-VI semiconductor quantum dot.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Impurity and defect interactions during laser thermal annealing in Ge

The microscopic mechanisms involving dopants, contaminants, and defects in Ge during pulsed melting laser thermal annealing (LTA) are investigated in detail. Samples both un-implanted and implanted with As or B are processed by LTA as well as characterized in terms of chemical (1D and 3D), electrical, and strain profiling. The clustering of As is directly measured by 3D chemical profiling and correlated with its partial electrical activation along with a reduction of the lattice strain induced by As atoms. A semi-quantitative microscopic model involving the interaction with mobile As-vacancy (AsV) complexes is proposed to describe the clustering mechanism. Boron is shown to follow different clustering behavior that changes with depth and marked by completely different strain levels. Oxygen penetrates from the surface into all the samples as a result of LTA and, only in un-implanted Ge, it occupies an interstitial position inducing also positive strain in the lattice. On the contrary, data suggest that the presence of As or B forces O to assume different configurations with negligible strain, through O-V or O-B interactions for the two dopant species, respectively. These data suggest that LTA does not inject a significant amount of vacancies in Ge, at variance with Si, unless As atoms or possibly other n-type dopants are present. These results have to be carefully considered for modeling the LTA process in Ge and its implementation in technology.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2020

Impact of a minority relativistic electron tail interacting with a thermal plasma containing high-atomic-number impurities

A minority relativistic electron component can arise in both laboratory and naturally-occurring plasmas. In the presence of high-atomic-number ion species, the ion charge state distribution at low bulk electron temperature can be dominated by relativistic electrons, even though their density is orders of magnitude lower. This is due to the relativistic enhancement of the collisional excitation and ionization cross sections. The resulting charge state effect can dramatically impact the radiative power loss rate and the related Bethe stopping power of relativistic electrons in a dilute plasma.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2014

Ab initio study of H, He, Li and Be impurity effect in tungsten Σ3{112} and Σ27{552} grain boundaries

Density functional theory calculations were performed to study the effects of H, He, Li and Be on the cohesion of W Σ3<110>{112} and Σ27<110>{552} grain boundaries (GBs). In Σ3, Li causes the strongest embrittlement, while in Σ27 it is He. In both GBs, H slightly reduces the cohesion. Compared to He and Li, H exhibits much stronger attractive binding with W that may inhibit subsequent segregation of Li and He to the GBs. In Σ3, Be decreases the cohesion. However, in Σ27, Be strengthens the cohesion in several interstitial positions by increasing the bonding across the interface or by inducing GB restructuring.

Ab Initio↗
DOE OSTI2021

Experimental evidence that zinc impurities pin pair-density-wave order in La 2-x Ba x CuO 4

Both Zn doping and c-axis magnetic fields have been observed to increase the spin stripe order in La 2-x Ba x CuO 4 with x close to 1/8. For x = 0.095, the applied magnetic field also causes superconducting layers to decouple, presumably by favoring pair-density-wave order that consequently frustrates interlayer Josephson coupling. Here we show that introducing 1% Zn also leads to an initial onset of two-dimensional (2D) superconductivity, followed by 3D superconductivity at lower temperatures, even in zero field. Overall, we infer that the Zn pins pair-density-wave order locally, establishing the generality of such behavior.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

The Influence of Copper Impurity on the Electronic Structure and Optical Properties of TmNi{sub 5} Compound

Investigations of the electronic structure and optical properties of TmNi{sub 5–х}Сu{sub x} (х = 0, 1, 2, 3) compounds were performed. Self-consistent calculations of the band spectrum have been performed in the local electron-spin-density approximation with a correction on strong electron interactions within the LSDA + U method. Total and partial densities of electron states associated with thulium, nickel, and copper atoms have been calculated. Optical conductivity, the behavior of which is interpreted for each compound taking into account the performed calculations, has been measured by the ellipsometry method in a wide wavelength range of 0.22–16 μm. Concentration dependences of plasma and relaxation frequencies of conduction electrons have been determined.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Impurity-induced photoconductivity of narrow-gap Cadmium–Mercury–Telluride structures

The photoconductivity (PC) spectra of CdHgTe (MCT) solid solutions with a Cd fraction of 17 and 19% are measured. A simple model for calculating the states of doubly charged acceptors in MCT solid solutions, which makes it possible to describe satisfactorily the observed photoconductivity spectra, is proposed. The found lines in the photoconductivity spectra of narrow-gap MCT structures are associated with transitions between the states of both charged and neutral acceptor centers.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Specific Features of the Electron Spin Resonance of an Iron Impurity in HgSe Crystals

The electron-spin-resonance spectra of transition metal ions Fe in the HgSe matrix are analyzed. The spectra have an appearance typical of the Fe{sup 3+} ion, i.e., they consist of five fine-structure lines with a splitting that corresponds to a weak crystal field. The spectra are observed at temperatures of up to 50 K. The spectral lines are deformed and have a Dyson shape. An analysis of the temperature dependences of the line amplitudes shows that a transition from paramagnetic ordering to ferromagnetic ordering occurs with decreasing temperature, with the Curie temperature T ≈ 7 K.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Structure of Se{sub 95}As{sub 5} Chalcogenide Glassy Semiconductor Doped by EuF{sub 3} Impurity

The local structure of film samples of the chalcogenide glassy semiconductors Se{sub 95}As{sub 5} and Se{sub 95}As{sub 5}(EuF{sub 3}){sub x} (x = 0.01–1 at %) are studied by X-ray diffraction and Raman scattering. The “quasiperiod” of the structure, the correlation length, the structural elements, and the chemical bonds, which form the amorphous matrix of the investigated materials, are determined. The obtained results are interpreted within the framework of the Elliott void–cluster model taking into account the chemical activity of europium ions.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Superhyperfine Structure of the EPR Spectra of Nd{sup 3+} Impurity Ions in Fluorite CaF{sub 2}

EPR spectra of a CaF{sub 2} single crystal that was grown from melt containing a small addition of NdF{sub 3} were studied. Signals corresponding to tetragonal centers of Nd{sup 3+} ions and cubic centers of Er3+ and Yb3+ ions were found. Superhyperfine structure (SHFS) in the spectra of the Nd{sup 3+} ions was observed for the first time in this crystal; parameters of the superhyperfine interaction of the Nd{sup 3+} ions with the nearest nine fluorine ions were determined. The dependence of the resolution of the Nd{sup 3+} EPR spectrum SHFS on the incident microwave power at the temperature of T ≈ 6 K was studied. Obtained results are discussed and compared with the literature data.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Kinetics of Pulse Cathodoluminescence in Lithium–Gadolinium Orthoborate Crystals Doped with Cerium Impurity

The relaxation kinetics of electron excitations in single-crystal and crystal-fiber Li{sub 6}GdB{sub 3}O{sub 9} samples was studied by the time-resolved methods of pulse absorption spectroscopy and pulse cathodoluminescence under excitation with a nanosecond electron beam at 293 K. Based on the results of the numerical modeling of recombination processes, a pulse cathodoluminescence excitation mechanism was proposed.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

The Influence of the Surface Neutralization of Active Impurities on the Field-Electron Emission Properties of p-Type Silicon Crystals

Correlation dependences between variations of the structural-phase composition, morphology characteristics, and field-electron-emission (FEE) properties of surface-structured p-type silicon singlecrystalline (100)-oriented wafers have been studied during their stepwise high-dose carbon-ion-beam irradiation. It is established that the stepwise implantation of carbon decreases the FEE threshold and favors an increase in the maximum FEE-current density by more than two orders of magnitude. Physicochemical mechanisms involved in this modification of the properties of near-surface layers of silicon under carbon-ion implantation are considered.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗