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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 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Structures and localized vibrational states of defects in graphite by tight-binding calculations

The structural and vibrational properties of pristine graphite and point defects in graphite are studied by tight-binding (TB) calculations using a three-center TB potential model. We showed that the three-center TB potential without ‘‘ad hoc’’ van der Waals interaction corrections can accurately describe the inter-layer distance of graphite and the lowest-energy structures and stabilities of typical point defects in graphite. The results from our TB calculations are in good agreement with those from density-functional theory calculations with van der Waals interaction corrections. We also investigated the vibrational properties to gain better understanding on the localization of vibrational states induced by the point defects. Our calculation results show that although localized or quasi-localized vibrational modes can be found in all defected graphite, the localization induced by Frenkel pair, dual-vacancy, and dual-interstitial defects is much stronger. Atomic displacements associated with the localized vibrational modes induced by these three point defects are also analyzed

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Highly mobile charge-transfer excitons in two-dimensional WS 2 /tetracene heterostructures

Charge-transfer (CT) excitons at heterointerfaces play a critical role in light to electricity conversion using organic and nanostructured materials. However, how CT excitons migrate at these interfaces is poorly understood. We investigate the formation and transport of CT excitons in two-dimensional WS 2 /tetracene van der Waals heterostructures. Electron and hole transfer occurs on the time scale of a few picoseconds, and emission of interlayer CT excitons with a binding energy of ~0.3 eV has been observed. Transport of the CT excitons is directly measured by transient absorption microscopy, revealing coexistence of delocalized and localized states. Trapping-detrapping dynamics between the delocalized and localized states leads to stretched-exponential photoluminescence decay with an average lifetime of ~2 ns. The delocalized CT excitons are remarkably mobile with a diffusion constant of ~1 cm 2 s -1 . These highly mobile CT excitons could have important implications in achieving efficient charge separation.

36 MATERIALS SCIENCE↗
DOE OSTI2015

A very general rate expression for charge hopping in semiconducting polymers

We propose an expression of the hopping rate between localized states in semiconducting disordered polymers that contain the most used rates in the literature as special cases. We stress that these rates cannot be obtained directly from electron transfer rate theories as it is not possible to define diabatic localized states if the localization is caused by disorder, as in most polymers, rather than nuclear polarization effects. After defining the separate classes of accepting and inducing nuclear modes in the system, we obtain a general expression of the hopping rate. We show that, under the appropriate limits, this expression reduces to (i) a single-phonon rate expression or (ii) the Miller-Abrahams rate or (iii) a multi-phonon expression. The description of these limits from a more general expression is useful to interpolate between them, to validate the assumptions of each limiting case, and to define the simplest rate expression that still captures the main features of the charge transport. When the rate expression is fed with a range of realistic parameters the deviation from the Miller-Abrahams rate is large or extremely large, especially for hopping toward lower energy states, due to the energy gap law.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Exotic edge states of C 3 high-fold fermions in honeycomb lattices

A generalization of the graphene honeycomb model to the case where each site in the honeycomb lattice contains a n -fold degenerate set of eigenstates of the C 3 symmetry has been recently proposed to describe several systems, including triangulene crystals and photonic lattices. These generalized honeycomb models are defined by ( n a , n b ) , the number of C 3 eigenstates in the a and b sites of the unit cell, resulting in n a + n b bands. Thus, the (1,1) case gives the coventional honeycomb model that describes the two low-energy bands in graphene. Generalizations, such as (2,1), (2,2), and (3,3) display several nontrivial features, such as coexisting graphenelike Dirac cones with flat bands, both at zero and finite energy, as well as robust degeneracy points where a flat band and a parabolic band meet at the Γ point. Here we explore the edge states of this class of crystals, using as reference triangulene crystals, and we find several types of edge states absent in the conventional (1,1) honeycomb case, associated to the nontrivial features of the two-dimensional bands of the high-fold case. First, we find dispersive edge states associated to the finite-energy flat bands, that occur both at the armchair and zigzag termination. Second, in the case of noncentrosymmetric triangulene crystals that lead to a S = 1 Dirac band, we have a bonding-antibonding pair of dispersive edge states, localized in the same edge so that their energy splitting is reduced as their localization increases, opposite to the conventional behavior of pairs of states localized in opposite edges. Third, for the (3,3) case, that hosts a gap separating a pair of flat conduction and valence bands, we find nondispersive edge states with E = 0 in all edge terminations. Published by the American Physical Society 2024

Madail, L. (ORCID:0000000208457748)↗
NASA NTRS1951

Theory of thin-walled rods

Starting with the Love equations for bending of extensible shells, "principal stress states" are sought for a thin-walled rod of arbitrary but open cross section. Principal stress states exclude those local states arising from end conditions which damp out with distance from the ends. It is found that for rods of intermediate length, long enough to avoid local bending at a support, and short enough that elementary torsion and bending are not the most significant stress states, four principal states exist. Three of these states are associated with the planar distribution of axial stress and are equivalent to the engineering theory of extension and bending of solid sections. The fourth state resembles that which has been called in the literature "bending stress due to torsional", except that cross sections are permitted to bend and the shear along the center line of the cross section is permitted to differ from zero.

LOADS AND STRESSES, STRUCTURAL - TENSION↗
DOE OSTI2024

Probing scrambling and operator size distributions using random mixed states and local measurements

The dynamical spreading of quantum information through a many-body system, typically called scrambling, is a complex process that has proven to be essential to describe many properties of out-of-equilibrium quantum systems. Scrambling can, in principle, be fully characterized via the use of out-of-time-ordered correlation functions, which are notoriously hard to access experimentally. In this work, we put forward an alternative toolbox of measurement protocols to experimentally probe scrambling by accessing properties of the operator size probability distribution, which tracks the size of the support of observables in a many-body system over time. Our measurement protocols require the preparation of separable mixed states together with local operations and measurements, and combine the tools of randomized operations, a modern development of near-term quantum algorithms, with the use of mixed states, a standard tool in NMR experiments. We demonstrate how to efficiently probe the probability-generating function of the operator distribution and discuss the challenges associated with obtaining the moments of the operator distribution. We further show that manipulating the initial state of the protocol allows us to directly obtain the individual elements of the distribution for small system sizes. Published by the American Physical Society 2024

Blocher, Philip Daniel (ORCID:0000000163027567)↗
DOE OSTI2019

The third law of thermodynamics in open quantum systems

In this work, we consider open quantum systems consisting of a finite system of independent fermions with arbitrary Hamiltonian coupled to one or more equilibrium fermion reservoirs (which need not be in equilibrium with each other). A strong form of the third law of thermodynamics, S(T) → 0 as T → 0, is proven for fully open quantum systems in thermal equilibrium with their environment, defined as systems where all states are broadened due to environmental coupling. For generic open quantum systems, it is shown that S(T) → g ln 2 as T → 0, where g is the number of localized states lying exactly at the chemical potential of the reservoir. For driven open quantum systems in a nonequilibrium steady state, it is shown that the local entropy S(x;T)→0 as T(x) → 0, except for cases of measure zero arising due to localized states, where T(x) is the temperature measured by a local thermometer.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

A novel resource sharing algorithm based on distributed construction for radiant enclosure problems

This study demonstrates a novel approach to solving inverse radiant enclosure problems based on distributed construction. Specifically, the problem of determining the temperature distribution needed on the heater surfaces to achieve a desired design surface temperature profile is recast as a distributed construction problem in which a shared resource, temperature, is distributed by computational agents moving blocks. The sharing of blocks between agents enables them to achieve their desired local state, which in turn achieves the desired global state. Each agent uses the current state of their local environment and a simple set of rules to determine when to exchange blocks, each block representing a discrete unit of temperature change. This algorithm is demonstrated using the established two-dimensional inverse radiation enclosure problem. The temperature profile on the heater surfaces is adjusted to achieve a desired temperature profile on the design surfaces. The resource sharing algorithm was able to determine the needed temperatures on the heater surfaces to obtain the desired temperature distribution on the design surfaces in the nine cases examined.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2019

Multifaceted machine learning of competing orders in disordered interacting systems

While the nonperturbative interaction effects in the fractional quantum Hall regime can be readily simulated through exact diagonalization, it has been challenging to establish a suitable diagnostic that can label different phases in the presence of competing interactions and disorder. Here we introduce a multifaceted framework using a simple artificial neural network (ANN) to detect defining features of a fractional quantum Hall state, a charge-density-wave state and a localized state using the entanglement spectra and charge density as independent input. We consider the competing effects of a perturbing interaction (l = 1 pseudopotential ΔV 1 ) , a disorder potential W, and the Coulomb interaction to the system at filling fraction ν = 1/3. In this work, our phase diagram benchmarks well against previous estimates of the phase boundary along the axes of our phase diagram where other measures exist. Moreover, exploring the entire two-dimensional phase diagram, we establish the robustness of the fractional quantum Hall state and map out the charge-density-wave microemulsion phase wherein droplets of the charge-density-wave region appear before the charge density wave is completely disordered. Hence we establish that the ANN can access and learn the defining traits of topological as well as broken symmetry phases using multifaceted inputs of entanglement spectra and charge density.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2012

Intrinsic inhomogeneities of low-doped lanthanum manganites in the paramagnetic temperature range

The nature of the electrical resistivity for low-doped lanthanum manganites is elucidated. The electrical resistivity is described by the Efros-Shklovskii law (ln{rho} {radical} (T{sub 0}/T){sup -1/2}, where T{sub 0} {radical} 1/R{sub ls}) in the temperature range from T* Almost-Equal-To 300 K Almost-Equal-To T{sub C} (T{sub C} is the Curie temperature for conducting manganites) to their T{sub C} and is explained by the tunneling of carriers between localized states. The magnetoresistance is explained by a change in the size of localized states R{sub ls} in a magnetic field. The patterns of change in R{sub ls} with temperature and magnetic field strength determined from magnetotransport properties are satisfactorily described in the model of phase separation into small-radius metallic droplets in a paramagnetic matrix. The sizes R{sub ls} and their temperature dependence have been estimated through magnetic measurements. The results confirm the existence of a Griffith phase. The intrinsic inhomogeneities produced by thermodynamic phase separation determine the electrical resistivity and magnetoresistance of lanthanum manganites.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Structural transition, subgap states, and carrier transport in anion-engineered zinc oxynitride nanocrystalline films

In this work, anion alloying is engineered in ZnON nanocrystalline films, and the resultant evolution of the structural transition, subgap states, and carrier transport is investigated. A broad distribution of sub-gap states above the valence band maximum is introduced by nitrogen due to the hybridization of N 2p and O 2p orbitals. The phase transition from partially amorphous states to full crystallinity occurs above a characteristic growth temperature of 100 °C, and the localized states are suppressed greatly due to the reduction of nitrogen composition. The electronic properties are dominated by grain boundary scattering and electron transport across boundary barriers through thermal activation at band edge states at high temperatures. The conductivity below 130 K exhibits a weak temperature dependence, which is a signature of variable-range hopping conduction between localized states introduced by nitrogen incorporation.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2022

Williston Basin Carbon Ore, Rare Earth, and Critical Minerals (CORE-CM) Program

The U.S. Department of Energy’s Office of Fossil Energy awarded 13 CORE-CM programs as part of the CORE-CM Initiative, designed to develop the technology and upstream and midstream supply chains to extract rare-earth elements (REEs) and critical minerals (CMs) from the nation’s coal supplies. The intent is to catalyze regional economic growth and job creation while strengthening the use of domestic resources. The Williston Basin CORE-CM Program aims to drive the expansion and transformation of coal and coal-based resource usage within the Williston Basin to produce REEs, CMs, and nonfuel carbon-based products (CBPs). The work constitutes Phase 1 of a long-term program. The objectives of Phase 1 are to identify the existing knowledge base and gaps and to develop a series of assessments/plans, including an initial basinal assessment; a characterization and data acquisition plan; a waste stream reuse plan; a basinal strategies assessment for infrastructure, industries, and business; a technology assessment, development, and field testing plan; a technology innovation center plan(s); and a stakeholder outreach and education plan. The goal of this project is to initiate the development of a new industry in the resource-rich Williston Basin that will catalyze economic growth and job creation through a coalition team of private industry, university, and state, local, and federal government entities. A coalition team of nearly 30 private industry, university, and state, local, and federal government partners was formed for this program. Partners include the University of North Dakota Energy & Environmental Research Center, Institute for Energy Studies, and Nistler College; North Dakota State University; Montana Tech University; Pacific Northwest National Laboratory; Critical Materials Institute; North Dakota Geological Survey; South Dakota Geological Survey; U.S. Geological Survey; North American Coal Corporation; BNI Energy; Basin Electric Power Cooperative; Minnkota Power Cooperative; and many more.

Kay, John P.↗
DOE OSTI2023

Williston Basin Carbon Ore, Rare Earth, and Critical Minerals (CORE-CM) Program

The U.S. Department of Energy’s (DOE’s) Office of Fossil Energy awarded 13 Carbon Ore, Rare-Earth and Critical Minerals (CORE-CM) programs as part of the CORE-CM Initiative, designed to develop the technology and upstream and midstream supply chains to extract rare-earth elements (REEs) and CMs from the nation’s coal supplies. The intent is to catalyze regional economic growth and job creation while strengthening the use of domestic resources. The Williston Basin CORE-CM Program aims to drive the expansion and transformation of coal and coal-based resource usage within the Williston Basin to produce REEs, CMs, and nonfuel carbon-based products (CBPs). The work constitutes Phase 1 of a long-term program. The objectives of Phase 1 are to identify the existing knowledge base and gaps and to develop a series of assessments/plans, including an initial basinal assessment; a characterization and data acquisition plan; a waste stream reuse plan; a basinal strategies assessment for infrastructure, industries, and business; a technology assessment, development, and field-testing plan; a technology innovation center plan(s); and a stakeholder outreach and education plan. Originally, the CORE-CM programs were to do little if any sample collection as part of the Phase 1 program. As part of the ongoing interactions with DOE regarding the progress of the 13 CORE-CM programs, DOE has decided to extend Phase 1 with additional funding to allow all of the Phase 1 CORE-CM programs to collect and characterize more samples that have potential to be sources of REEs and CMs. The goal of this project is to initiate the development of a new industry in the resource-rich Williston Basin that will generate economic growth and job creation through a coalition team of private industry; university; and state, local, and federal government entities. A coalition team of nearly 30 private industry; university; and state, local, and federal government partners was formed for this program. Partners include the University of North Dakota Energy & Environmental Research Center, Institute for Energy Studies, and Nistler College; North Dakota State University; Montana Tech University; Pacific Northwest National Laboratory; Critical Materials Institute; North Dakota Geological Survey; South Dakota Geological Survey; U.S. Geological Survey; North American Coal Corporation; BNI Energy; Basin Electric Power Cooperative; Minnkota Power Cooperative; and many more.

Kay, John P.↗
DOE OSTI2015

Disorder-free localization around the conduction band edge of crossing and kinked silicon nanowires

We explore ballistic regime quantum transport characteristics of oxide-embedded crossing and kinked silicon nanowires (NWs) within a large-scale empirical pseudopotential electronic structure framework, coupled to the Kubo-Greenwood transport analysis. A real-space wave function study is undertaken and the outcomes are interpreted together with the findings of ballistic transport calculations. This reveals that ballistic transport edge lies tens to hundreds of millielectron volts above the lowest unoccupied molecular orbital, with a substantial number of localized states appearing in between, as well as above the former. We show that these localized states are not due to the oxide interface, but rather core silicon-derived. They manifest the wave nature of electrons brought to foreground by the reflections originating from NW junctions and bends. Hence, we show that the crossings and kinks of even ultraclean Si NWs possess a conduction band tail without a recourse to atomistic disorder.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2012

The effect of coulomb correlations on the nonequilibrium charge redistribution tuned by the tunneling current

We demonstrate that the tunneling current flowing through a system with Coulomb correlations leads to a charge redistribution between the different localized states. A simple model consisting of two electron levels is analyzed by means of the Heisenberg equations of motion taking correlations of electron filling numbers in localized states into account exactly in all orders. We consider various relations between the Coulomb interaction and localized electron energies. Sudden jumps of the electron density at each level in a certain range of the applied bias are found. We find that for some parameter range, inverse occupation in the two-level system appears due to Coulomb correlations. It is also shown that Coulomb correlations lead to the appearance of negative tunneling conductivity at a certain relation between the values of tunneling rates from the two electron levels.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

Visualization of Mesoscopic Conductivity Fluctuations in Amorphous Semiconductor Thin-Film Transistors

Charge transport in amorphous semiconductors is considerably more complicated than the process in crystalline materials due to abundant localized states. In addition to device-scale characterization, spatially resolved measurements are important to unveiling electronic properties. Here, we report gigahertz conductivity mapping in amorphous indium gallium zinc oxide (a-IGZO) thin-film transistors by microwave impedance microscopy (MIM), which probes conductivity without Schottky barrier’s influence. The difference between the dc and microwave conductivities reflects the efficacy of the injection barrier in an accumulation-mode transistor. The conductivity exhibits significant nanoscale inhomogeneity in the subthreshold regime, presumably due to trapping and release from localized states. The characteristic length scale of local fluctuations, as determined by the autocorrelation analysis, is about 200 nm. Using a random-barrier model, we can simulate the spatial variation of the potential landscape, which underlies the mesoscopic conductivity distribution. Furthermore, our work provides an intuitive way to understand the charge transport mechanism in amorphous semiconductors at the microscopic level.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Incident Management Preparedness and Coordination Toolkit

As with many professions, safety planners and first responders tend to be specialists in certain areas. To be truly useful, tools should be tailored to meet their specific needs. Thus, general software suites aimed at the professional geographic information system (GIS) community might not be the best solution for a first responder with little training in GIS terminology and techniques. On the other hand, commonly used web-based map viewers may not have the capability to be customized for the planning, response, and recovery (PR&R) mission. Data formats should be open and foster easy information flow among local, state, and federal partners. Tools should be free or low-cost to address real-world budget constraints at the local level. They also need to work both with and without a network connection to be robust. The Incident Management Preparedness and Coordination Toolkit (IMPACT) can satisfy many of these needs while working in harmony with established systems at the local, state, and federal levels. The IMPACT software framework, termed the Geospatial Integrated Problem Solving Environment (GIPSE), organizes tasks, tools, and resources for the end user. It uses the concept of software wizards to both customize and extend its functionality. On the Tasks panel are a number of buttons used to initiate various operations. Similar to macros, these task buttons launch scripts that utilize the full functionality of the underlying foundational components such as the SQL spatial database and ORNL-developed map editor. The user is presented with a series of instruction pages which are implemented with HTML for interactivity. On each page are links which initiate specific actions such as creating a map showing various features. Additional tasks may be quickly programmed and added to the panel. The end user can customize the graphical interface to faciltate its use during an emergency. One of the major components of IMPACT is the ORNL Geospatial Viewer (OGV). It is used to provide various map displays for the Tasks and Maps panels. Unlike typical maps however, the OGV display is highly interactive and can be customized, automated, and animated to meet the needs of the user. It is also a means to both import and export geospatial data from or to existing GIS systems. The built-in simulation capability can be used as the basis of table-top exercises.

Koch, Daniel B.↗