Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “Many electron systems”

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 1,117 records · Page 62
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Precision measurement of electron-electron scattering in GaAs/AlGaAs using transverse magnetic focusing

Electron-electron (e-e) interactions assume a cardinal role in solid-state physics. Quantifying the e-e scattering length is hence critical. In this paper we show that the mesoscopic phenomenon of transverse magnetic focusing (TMF) in two-dimensional electron systems forms a precise and sensitive technique to measure this length scale. Conversely we quantitatively demonstrate that e-e scattering is the predominant effect limiting TMF amplitudes in high-mobility materials. Using high-resolution kinetic simulations, we show that the TMF amplitude at a maximum decays exponentially as a function of the e-e scattering length, which leads to a ready approach to extract this length from the measured TMF amplitudes. The approach is applied to measure the temperature-dependent e-e scattering length in high-mobility GaAs/AlGaAs heterostructures. The simulations further reveal current vortices that accompany the cyclotron orbits - a collective phenomenon counterintuitive to the ballistic transport underlying a TMF setting.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Adaptive basis sets for practical quantum computing

Electronic structure calculations on small systems such as H 2 , H 2 O, LiH, and BeH 2 with chemical accuracy are still a challenge for the current generation of noisy intermediate-scale quantum (NISQ) devices. One of the reasons is that due to the device limitations, only minimal basis sets are commonly applied in quantum chemical calculations, which allows one to keep the number of qubits employed in the calculations at a minimum. However, the use of minimal basis sets leads to very large errors in the computed molecular energies as well as potential energy surface shapes. One way to increase the accuracy of electronic structure calculations is through the development of small basis sets better suited for quantum computing. In this work, we show that the use of adaptive basis sets, in which exponents and contraction coefficients depend on molecular structure, provides an easy way to dramatically improve the accuracy of quantum chemical calculations without the need to increase the basis set size and thus the number of qubits utilized in quantum circuits. As a proof of principle, we optimize an adaptive minimal basis set for quantum computing calculations on an H 2 molecule, in which exponents and contraction coefficients depend on the H—H distance, and apply it to the generation of H 2 potential energy surface on IBM-Q quantum devices. The adaptive minimal basis set reaches the accuracy of the double-zeta basis sets, thus allowing one to perform double-zeta quality calculations on quantum devices without the need to utilize twice as many qubits in simulations. This approach can be extended to other molecular systems and larger basis sets in a straightforward manner.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2025

Mechanistic Insights into Visible-Light-Induced ATRA Reactions Powered by the Symbiotic Relationship between Cu(II)/Cu(I) Phenanthroline Complexes

As photoredox catalysis continues to yield promising chemical transformations, there is an increased need to understand how specific photocatalysts function to improve reaction efficiencies while expanding their scope. Copper-phenanthroline-based photocatalysts such as Cu II (dap)Cl 2 (dap = 2,9-di(p-anisyl)-1,10-phenanthroline) and [Cu I (dap) 2 ]Cl were both found to be equally capable of olefin activation through electrophilic atom transfer radical addition (ATRA) reactions. Although these molecular catalysts have proven successful, many intermediates suggested in the proposed catalytic cycles have never been detected. One undetermined aspect in this chemistry is related to how one equivalent of Cu II (dap)Cl 2 generates half of an equivalent of [Cu I (dap) 2 ] + during the photocatalytic sequence. To this end, we initially used more synthetically accessible model systems, namely, [Cu I (dpp) 2 ]Cl and Cu II (dpp)Cl 2 (dpp = 2,9-diphenyl-1,10-phenanthroline), to glean detailed mechanistic insights into this unusual symbiotic relationship. We directly detected several intermediates involved in the ATRA photocatalytic cycle using these model chromophores in conjunction with electronic spectroscopy, infrared matrix-assisted laser desorption electrospray ionization (IR-MALDESI) mass spectrometry, electronic structure calculations, EPR spin-trap experiments, and 1 H NMR spectroscopy. We found that the unique ligand lability and coordinating properties of acetonitrile enable both the in situ oxidation of [Cu I (dpp) 2 ] + by tosyl chloride into Cu II (dpp)Cl 2 and the visible-light-induced homolysis of the Cu II –Cl bond, which initiates the conversion to the Cu I species [Cu I (dpp) 2 ][Cu I Cl 2 ]. Here, the combined findings from the present study of the catalytic cycle demonstrate that the symbiotic relationship between Cu II (dpp)Cl 2 and [Cu I (dpp) 2 ] + , as well as between Cu II (dap)Cl 2 and [Cu I (dap) 2 ] + , is the critical factor enabling the ATRA photoreaction by departing from either photocatalyst.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Fingerprinting shock-induced deformations via diffraction

Abstract During the various stages of shock loading, many transient modes of deformation can activate and deactivate to affect the final state of a material. In order to fundamentally understand and optimize a shock response, researchers seek the ability to probe these modes in real-time and measure the microstructural evolutions with nanoscale resolution. Neither post-mortem analysis on recovered samples nor continuum-based methods during shock testing meet both requirements. High-speed diffraction offers a solution, but the interpretation of diffractograms suffers numerous debates and uncertainties. By atomistically simulating the shock, X-ray diffraction, and electron diffraction of three representative BCC and FCC metallic systems, we systematically isolated the characteristic fingerprints of salient deformation modes, such as dislocation slip (stacking faults), deformation twinning, and phase transformation as observed in experimental diffractograms. This study demonstrates how to use simulated diffractograms to connect the contributions from concurrent deformation modes to the evolutions of both 1D line profiles and 2D patterns for diffractograms from single crystals. Harnessing these fingerprints alongside information on local pressures and plasticity contributions facilitate the interpretation of shock experiments with cutting-edge resolution in both space and time.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Anisotropic Two-Dimensional Disordered Wigner Solid

The interplay between the Fermi sea anisotropy, electron-electron interaction, and localization phenomena can give rise to exotic many-body phases. An exciting example is an anisotropic two-dimensional (2D) Wigner solid (WS), where electrons form an ordered array with an anisotropic lattice structure. Such a state has eluded experiments up to now as its realization is extremely demanding: First, a WS entails very low densities where the Coulomb interaction dominates over the kinetic (Fermi) energy. Attaining such low densities while keeping the disorder low is very challenging. Second, the low-density requirement has to be fulfilled in a material that hosts an anisotropic Fermi sea. Here, we report transport measurements in a clean (low-disorder) 2D electron system with anisotropic effective mass and Fermi sea. The data reveal that at extremely low electron densities, when the r s parameter, the ratio of the Coulomb to the Fermi energy, exceeds ≃ 38, the current-voltage characteristics become strongly nonlinear at small dc biases. Several key features of the nonlinear characteristics, including their anisotropic voltage thresholds, are consistent with the formation of a disordered, anisotropic WS pinned by the ubiquitous disorder potential.

42 ENGINEERING↗
NASA NTRS1973

Chemical reactivity of hydrogen, nitrogen, and oxygen atoms at temperatures below 100 k

The synthesis of unusual compounds by techniques employing cryogenic cooling to retard their very extreme reactivity was investigated. Examples of such species that were studied are diimide (N2H2), cyclobutadiene (C4H4), cyclopropanone (C3H4O), oxirene (C2H2O), and many others. Special purpose cryogenically cooled inlet arrangements were designed such that the analyses incurred no warm-up of the cold, and frequently explosively unstable, compounds. Controlled energy electron impact techniques were used to measure critical potentials and to develop the molecular energetics and thermodynamics of these molecules and to gain some insight into their kinetic characteristics as well. Three and four carbon strained ring molecules were studied. Several reactions of oxygen and hydrogen atoms with simple molecules of H, N, C, and O in hard quench configurations were studied. And the quench stabilization of BH3 was explored as a model system in cryochemistry.

Mcgee, H. A., Jr.↗
NASA NTRS1975

Error analysis of penetrator impacts on bodies without atmospheres

Penetrators are missile shaped objects designed to implant electronic instrumentation in various of surface materials with a nominal impact speed around 150 m/sec. An interest in the application of this concept to in situ subsurface studies of extra terrestrial bodies and planetary satellites exists. Since many of these objects do not have atmospheres, the feasibility of successfully guiding penetrators to the required near-zero angle-of-attack impact conditions in the absence of an atmosphere was analyzed. Two potential targets were included, i.e., the moon and Mercury and several different penetrator deployment modes were involved. Impact errors arising from open-loop and closed-loop deployment control systems were given particular attention. Successful penetrator implacement requires: (1) that the impact speed be controlled, nominally to 150 m/sec, (2) that the angle of attack be in range 0 deg - 11 deg at impact, and (3) that the impact flight path angle be with 15 deg of vertical.

Davis, D. R.↗
NASA NTRS1987

Research and technology, 1987

Three broad goals were presented by NASA as a guide to meet the challenges of the future: to advance scientific knowledge of the planet Earth, the solar system, and the universe; to expand human presence beyond the Earth into the solar system; and to strengthen aeronautics research and technology. Near-term and new-generation space transportation and propulsion systems are being analyzed that will assure the nation access to and presence in space. Other key advanced studies include large astronomical observatories, space platforms, scientific and commercial payloads, and systems to enhance operations in Earth orbit. Longer-range studies include systems that would allow humans to explore the Moon and Mars during the next century. Research programs, both to support the many space missions studied or managed by the Center and to advance scientific knowledge in selected areas, involve work in the areas of atmospheric science, earth science, space science (including astrophysics and solar, magnetospheric, and atomic physics), and low-gravity science. Programs and experiment design for flights on the Space Station, free-flying satellites, and the Space Shuttle are being planned. To maintain a leadership position in technology, continued advances in liquid and solid propellant engines, materials and processes; electronic, structural, and thermal investigations; and environmental control are required. Progress during the fiscal year 1987 is discussed.

Source record↗
NASA NTRS1990

AlSb/InAs/AlSb quantum wells

Researchers studied the InAs/AlSb system recently, obtaining 12nm wide quantum wells with room temperature mobilities up to 28,000 cm(exp 2)/V center dot S and low-temperature mobilities up to 325,000 cm(exp 2)/V center dot S, both at high electron sheet concentrations in the 10(exp 12)/cm(exp 2) range (corresponding to volume concentrations in the 10(exp 18)/cm(exp 2) range). These wells were not intentionally doped; the combination of high carrier concentrations and high mobilities suggest that the electrons are due to not-intentional modulation doping by an unknown donor in the AlSb barriers, presumably a stoichiometric defect, like an antisite donor. Inasmuch as not intentionally doped bulk AlSb is semi-insulating, the donor must be a deep one, being ionized only by draining into the even deeper InAs quantum well. The excellent transport properties are confirmed by other observations, like excellent quantum Hall effect data, and the successful use of the quantum wells as superconductive weak links between Nb electrodes, with unprecendentedly high critical current densities. The system is promising for future field effect transistors (FETs), but many processing problems must first be solved. Although the researchers have achieved FETs, the results so far have not been competitive with GaAs FETs.

Kroemer, Herbert↗
NASA NTRS1992

A transportronic solution to the problem of interorbital transportation

An all-electronic transportation system described by the term 'transportronics' is examined as a means of solving the current problem of the high cost of transporting material from low-Earth orbit (LEO) to geostationary orbit (GEO). In this transportation system, low cost electric energy at the surface of the Earth is efficiently converted into microwave power which is then efficiently formed into a narrow beam which is kept incident upon the orbital transfer vehicles (OTV's) by electronic tracking. The incident beam is efficiently captured and converted into DC power by a device which has a very high ratio of DC power output to its mass. Because the mass of the electric thruster is also low, the resulting acceleration is unprecedented for electric-propelled vehicles. However, the performance of the system in terms of transit times from LEO to GEO is penalized by the short time of contact between the beam and the vehicle in low-Earth orbits. This makes it necessary to place the Earth based transmitters and the vehicles in the equatorial plane thus introducing many geopolitical factors. Technically, however, such a system as described in the report may out-perform any other approach to transportation in the LEO to GEO regime. The report describes and analyzes all portions of the beamed microwave power transmission system in considerable detail. An economic analysis of the operating and capital costs is made with the aid of a reference system capable of placing about 130,000 kilograms of payload into GEO each year. More mature states of the system are then examined, to a level in which 60,000 metric tons per year could be placed into GEO.

Brown, William C.↗
NASA NTRS2006

Evolution and Control of 2219 Aluminum Microstructural Features through Electron Beam Freeform Fabrication

Electron beam freeform fabrication (EBF3) is a new layer-additive process that has been developed for near-net shape fabrication of complex structures. EBF3 uses an electron beam to create a molten pool on the surface of a substrate. Wire is fed into the molten pool and the part translated with respect to the beam to build up a 3-dimensional structure one layer at a time. Unlike many other freeform fabrication processes, the energy coupling of the electron beam is extremely well suited to processing of aluminum alloys. The layer-additive nature of the EBF3 process results in a tortuous thermal path producing complex microstructures including: small homogeneous equiaxed grains; dendritic growth contained within larger grains; and/or pervasive dendritic formation in the interpass regions of the deposits. Several process control variables contribute to the formation of these different microstructures, including translation speed, wire feed rate, beam current and accelerating voltage. In electron beam processing, higher accelerating voltages embed the energy deeper below the surface of the substrate. Two EBF3 systems have been established at NASA Langley, one with a low-voltage (10-30kV) and the other a high-voltage (30-60 kV) electron beam gun. Aluminum alloy 2219 was processed over a range of different variables to explore the design space and correlate the resultant microstructures with the processing parameters. This report is specifically exploring the impact of accelerating voltage. Of particular interest is correlating energy to the resultant material characteristics to determine the potential of achieving microstructural control through precise management of the heat flux and cooling rates during deposition.

Taminger, Karen M.↗
NASA NTRS2015

Comparing and Contrasting Detectors: JWST NIR vs HST WFC3

In many ways, WFC3s IR channel is a good indicator for what to expect with JWST. There are some differences, most of which should be beneficial in JWST- JWSTs lower operating temperature will freeze out charge traps that would affect WFC3. Benefits should include lower dark current, lower persistence, and better reciprocity- JWSTs more recent HgCdTe process has lower defect density. The benefits are as described above- JWST uses better indium barriers. The benefits should include fewer RC type pixels. One area where more study might be beneficial is stability. The detector electronics play a significant role in determining how stable a detector system is(v.s. bias drifts and photometry). JWSTs SIDECARs are completely WFC3s Ball electronics- Studies comparing the bias and photometric stability of WFC3 and JWST might be useful to informing data acquisition and calibration strategies for JWST.

NIR↗
NASA NTRS2019

Cracking Problems in Low-Voltage Chip Ceramic Capacitors

Cracking remains the major reason of failures in multilayer ceramic capacitors (MLCCs) used in in space electronics. Due to a tight quality control of space-grade components, the probability that as manufactured capacitors have cracks is relatively low, and cracking is often occurs during assembly, handling and the following testing of the systems. Majority of capacitors with cracks are revealed during the integration and testing period, but although extremely rarely, defective parts remain undetected and result in failures during the mission. This situation is aggravated by manual soldering and rework that are often used during low volume production of circuit boards for space. Although failures of MLCCs are often attributed to the post-manufacturing stresses, in many cases they are due to a combination of certain deviations in the manufacturing processes that result in hidden defects in the parts and excessive stresses during assembly and use. This report gives an overview of design, manufacturing and testing processes of MLCCs focusing on elements related to cracking problems. The existing and new screening and qualification procedures and techniques are briefly described and assessed by their effectiveness in revealing cracks. The capability of different test methods to simulate stresses resulting in cracking, mechanisms of failures in capacitors with cracks, and possible methods of selecting the most robust to manual soldering stresses capacitors are discussed.

testing↗
NASA NTRSDate not supplied

Mass Spectrometer Observing Lunar Operations (MSoLo)

Introduction: In 2019, the National Aeronautics and Space Administration (NASA) announced that it would seek to have humans return to the moon by 2024 in the hopes of establishing a more sustainable lunar presence by 2028. This goal comes with many challenges, one of upmost importance will be to utilize resources that can be found on the moon. Water, which has been identified in the lunar Polar Regions, will be a key resource for in-situ resource utilization (ISRU), as it is capable of being processed for vehicular fuel, as well as life support systems materials such as oxygen. Upcoming Commercial Lunar Payload Services (CLPS) missions will be critical for these resource assessments. Methods: A modified commercial off-the-shelf (COTS) mass spectrometer developed at Kennedy Space Center known as MSolo, consisting of a quadrupole mass filter and space rated electronics undergoes testing and modifications in order to study operational parameters to unconventional approaches needed in flight situations. In general, MSolo operates in the 0-100 m/z range with the ability to detect with a faraday cup (FC) or an electron multiplier (EM) for enhanced detection. A crossbeam (XB) ionization source is used. Preliminary Data: Prior to construction, little information was available on how the MSolo system would perform at lunar like environments, factors such as temperatures (possible fluctuations from 70 to -45 °C), vibrations from launch and their side effects, the general ability to operate while the entire system (hardware and electronic components) were in a vacuum environment, were factors that while know to flight instruments, were something new to a modified COTS system. As components start to warm up, temperature becomes a key factor (ie. heat can no longer escape the electronics as no atmosphere is present), therefore it becomes crucial to find new ways to maintain stable signals and keep the instrument tuned. Calibration itself becomes an important parameter that needs to be performed while maintaining all flight like characteristics. Even the structure itself of MSolo’s sensor needed to be changed to survive the verification parameters needed to be approved for flight. Most important, all the modifications made to the COTS system have to keep the instrument working at the same specifications of the standard commercial systems. Novel Aspect: Results gathered provide key parameters that will assist to the unconventional mass spectrometry approaches of the upcoming CLPS missions to which MSolo has been selected to.

MSolo↗
NASA NTRS2019

Long Duration Venus Probes and Landers

Planetary probes have long been a tool used by scientists to gain early clues on environments and systems of new planetary targets. This not only fueled the scientific process but also helped prepare for future missions, such as landers, and helped ensure their success. Venus, Earth's sister planet, has been the target of more probes and landers than any other body in our solar system except for Earth and yet many fundamental questions are unanswered. Challenge for Venus Surface Science: This lack of knowledge is a result of the challenging Venus environments. Remote sensing of the surface and portions of the atmosphere is difficult at best due to the thick layers of sulfuric acid clouds and the high pressure supercritical CO2 atmosphere below those clouds. This has hampered the ability of orbiting missions to provide us insight into surface features and processes and thus hides potential clues on interior process from our view. Surface probes and landers face an even more daunting challenge, which is the extreme temperature, pressure and unfriendly chemical composition of the near surface atmosphere. Over 10 assets have landed on the surface yet the longest surviving asset Venera-13 lasted only 127 minutes before succumbing to the extreme temperature. While this and other landers provided valuable new data, the short life impacted ability to understand any temporal processes, for example meteorology, seismic active, and therefore very little is known about the interior and surface atmosphere interactions. New Capability Offering Potential Solutions: Re-cent developments by NASA are offering hope of overcoming the technical challenges of surface operations and life with the use of high temperature electronics and systems. Wide band gap, SiC based electronics have been demonstrated to function successfully for extended periods of time both at 500C, Venus surface temperatures as well as when temperature is combined with the reactive chemistry of the surface atmosphere and the high pressures (over 90 bar pressure at the surface). In addition to electronics a number of other subsystems are in development including power in the form of high temperature batteries and power management devices, communications including antennas, transmitters and other components, materials, and structures and mechanisms. These are all activities under NASA's Long Lived In situ Solar System Exploration (LLISSE) project. Other activities are also funded under NASA's HOTTech program.

Kremic, T.↗
DOE OSTI2022

Polariton enhanced free charge carrier generation in donor–acceptor cavity systems by a second-hybridization mechanism

Cavity quantum electrodynamics has been studied as a potential approach to modify free charge carrier generation in donor–acceptor heterojunctions because of the delocalization and controllable energy level properties of hybridized light–matter states known as polaritons. However, in many experimental systems, cavity coupling decreases charge separation. In this work, we theoretically study the quantum dynamics of a coherent and dissipative donor–acceptor cavity system, to investigate the dynamical mechanism and further discover the conditions under which polaritons may enhance free charge carrier generation. We use open quantum system methods based on single-pulse pumping to find that polaritons have the potential to connect excitonic states and charge separated states, further enhancing free charge generation on an ultrafast timescale of several hundred femtoseconds. The mechanism involves polaritons with optimal energy levels that allow the exciton to overcome the high Coulomb barrier induced by electron–hole attraction. Moreover, we propose that a second-hybridization between a polariton state and dark states with similar energy enables the formation of the hybrid charge separated states that are optically active. These two mechanisms lead to a maximum of 50% enhancement of free charge carrier generation on a short timescale. However, our simulation reveals that on the longer timescale of picoseconds, internal conversion and cavity loss dominate and suppress free charge carrier generation, reproducing the experimental results. Thus, our work shows that polaritons can affect the charge separation mechanism and promote free charge carrier generation efficiency, but predominantly on a short timescale after photoexcitation.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Zero-field spin resonance in graphene with proximity-induced spin-orbit coupling

In this work we investigate collective spin excitations in graphene with proximity-induced spin-orbit coupling (SOC) of the Rashba and valley-Zeeman types, as it is the case, e.g., for graphene on transition-metal-dichalcogenide substrates. It is shown that, even in the absence of an external magnetic field, such a system supports collective spin modes, which correspond to coupled oscillations of the uniform and valley-staggered magnetizations. These modes can be detected via both zero-field electron spin resonance (ESR) and zero-field electric-dipole spin resonance (EDSR), with EDSR response arising solely due to Rashba SOC. We analyze the effect of electron-electron interaction within the Fermi-liquid kinetic equation and show that the interaction splits both the ESR and EDSR peaks into two. The magnitude of splitting and the relative weights of the resonances can be used to extract the spin-orbit coupling constants and many-body interaction parameters that may not be accessible by other methods.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Real-time GW -BSE investigations on spin-valley exciton dynamics in monolayer transition metal dichalcogenide

We develop an ab initio nonadiabatic molecular dynamics (NAMD) method based on GW plus real-time Bethe-Salpeter equation (GW + rtBSE-NAMD) for the spin-resolved exciton dynamics. From investigations on MoS 2 , we provide a comprehensive picture of spin-valley exciton dynamics where the electron-phonon (e-ph) scattering, spin-orbit interaction (SOI), and electron-hole (e-h) interactions come into play collectively. In particular, we provide a direct evidence that e-h exchange interaction plays a dominant role in the fast valley depolarization within a few picoseconds, which is in excellent agreement with experiments. Moreover, there are bright-to-dark exciton transitions induced by e-ph scattering and SOI. Our study proves that e-h many-body effects are essential to understand the spin-valley exciton dynamics in transition metal dichalcogenides and the newly developed GW + rtBSE-NAMD method provides a powerful tool for exciton dynamics in extended systems with time, space, momentum, energy, and spin resolution.

36 MATERIALS SCIENCE↗