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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 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Bilayer Wigner crystals in a transition metal dichalcogenide heterostructure

One of the first theoretically predicted manifestations of strong interactions in many-electron systems was the Wigner crystal, in which electrons crystallize into a regular lattice. The crystal can melt via either thermal or quantum fluctuations. Quantum melting of the Wigner crystal is predicted to produce exotic intermediate phases and quantum magnetism because of the intricate interplay of Coulomb interactions and kinetic energy. However, studying two-dimensional Wigner crystals in the quantum regime has often required a strong magnetic field or a moiré superlattice potential, thus limiting access to the full phase diagram of the interacting electron liquid. Here we report the observation of bilayer Wigner crystals without magnetic fields or moiré potentials in an atomically thin transition metal dichalcogenide heterostructure, which consists of two MoSe 2 monolayers separated by hexagonal boron nitride. We observe optical signatures of robust correlated insulating states at symmetric (1:1) and asymmetric (3:1, 4:1 and 7:1) electron doping of the two MoSe 2 layers at cryogenic temperatures. Here, we attribute these features to bilayer Wigner crystals composed of two interlocked commensurate triangular electron lattices, stabilized by inter-layer interaction. The Wigner crystal phases are remarkably stable, and undergo quantum and thermal melting transitions at electron densities of up to 6 × 10 12 per square centimetre and at temperatures of up to about 40 kelvin. Our results demonstrate that an atomically thin heterostructure is a highly tunable platform for realizing many-body electronic states and probing their liquid–solid and magnetic quantum phase transitions.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Manipulating topological properties in Bi 2 Se 3 / BiSe /transition metal dichalcogenide heterostructures with interface charge transfer

Heterostructures of topological insulator Bi 2 Se 3 on transition metal dichalcogenides (TMDCs) offer a new materials platform for studying novel quantum states by exploiting the interplay among topological orders, charge orders and magnetic orders. Here, the diverse interface attributes, such as material combination, charge re-arrangement, defect and strain, can be utilized to manipulate the quantum properties of this class of materials. Recent experiments of Bi 2 Se 3 /NbSe 2 heterostructures show signatures of strong Rashba band splitting due to the presence of a BiSe buffer layer, but the atomic level mechanism is not fully understood. We conduct first-principles studies of the Bi 2 Se3/BiSe/TMDC heterostructures with five different TMDC substrates (1T phase VSe 2 , MoSe 2 , TiSe 2 , and 2H phase NbSe 2 , MoSe 2 ). We find significant charge transfer at both BiSe/TMDC and Bi 2 Se 3 /BiSe interfaces driven by the work function difference, which stabilizes the BiSe layer as an electron donor and creates interface dipole. The electric field of the interface dipole breaks the inversion symmetry in the Bi 2 Se 3 layer, leading to the giant Rashba band splitting in two quintuple layers and the recovery of the Dirac point in three quintuple layers, with the latter otherwise only occurring in thicker samples with at least six Bi 2 Se 3 quintuple layers. Besides, we find that strain can significantly affect the charge transfer at the interfaces. Our study presents a promising avenue for tuning topological properties in heterostructures of two-dimensional materials, with potential applications in quantum devices.

36 MATERIALS SCIENCE↗
NASA NTRS2012

Desert Research and Technology Studies (DRATS) Traverse Planning

Slide 1] The Desert Research and Technology Studies (DRATS) include large scale field tests of manned lunar surface exploration systems; these tests are sponsored by the Director s Office of Integration (DOI) [sic, Directorate Integration Office (DIO)] within the Constellation Program and they include geological exploration objectives along well designed traverses. These traverses are designed by the Traverse Team, an ad hoc group of some 10 geologists form NASA and academia, as well as experts in mission operation who define the operational constraints applicable to specific simulation scenarios. [Slide 2] These DRATS/DOI tests focus on 1) the performance of major surface systems, such as rovers, mobile habitats, communication architecture, navigation tools, earth-moving equipment, unmanned reconnaissance robots etc. under realistic field conditions and 2) the development of operational concepts that integrate all of these systems into a single, optimized operation. The participation of science is currently concentrating on geological sciences, with the objective of developing suitable tools and documentation protocols to sample representative rocks for Earth return, and to generate some conceptual understanding of the ground support structure that will be needed for the real time science-support of a lunar surface crew. [Slide 3] Major surface systems exercised in the June 2008 analog tests at the Moses Lake site, WA. [Upper left] The Chariot Rover (developed at Johnson Space Center) is an unpressurized vehicle driven by fully suited crews. [Upper right] Mobile Habitat provided by the Jet Propulsion Laboratory. Chariot is the more nimble and mobile vehicle and the idea is to drive the habitat remotely to some rendezvous place where Chariot would catch up - after a lengthy traverse - at the end of the day. [Lower left] The K-10 remotely operated robot (provided by NASA Ames Research Center) conducting scientific/geologic reconnaissance of the prospective traverse region, locating specific sites for more detailed exploration by Chariot and its crew. [Lower right] This earth-moving equipment (provided by NASA KSC) can be attached to Chariot and is envisioned to, for example, level an outpost site or to mine lunar soi

Horz, Friedrich↗
DOE OSTI2020

Materials Data on GaTe4(MoSe)4 by Materials Project

GaMo4Se4Te4 crystallizes in the cubic F-43m space group. The structure is three-dimensional. Mo+3.25+ is bonded in a 3-coordinate geometry to three equivalent Te2- and three equivalent Se2- atoms. All Mo–Te bond lengths are 2.94 Å. All Mo–Se bond lengths are 2.50 Å. Ga3+ is bonded in a tetrahedral geometry to four equivalent Te2- atoms. All Ga–Te bond lengths are 2.58 Å. Te2- is bonded in a 1-coordinate geometry to three equivalent Mo+3.25+ and one Ga3+ atom. Se2- is bonded in a 12-coordinate geometry to three equivalent Mo+3.25+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on MoSeS by Materials Project

MoSSe is Molybdenite-derived structured and crystallizes in the trigonal P-3m1 space group. The structure is two-dimensional and consists of two MoSSe sheets oriented in the (0, 0, 1) direction. Mo4+ is bonded to three equivalent Se2- and three equivalent S2- atoms to form distorted edge-sharing MoSe3S3 pentagonal pyramids. All Mo–Se bond lengths are 2.54 Å. All Mo–S bond lengths are 2.43 Å. Se2- is bonded in a 3-coordinate geometry to three equivalent Mo4+ atoms. S2- is bonded in a 3-coordinate geometry to three equivalent Mo4+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on MoSeS by Materials Project

MoSSe is Molybdenite-derived structured and crystallizes in the orthorhombic Amm2 space group. The structure is two-dimensional and consists of one MoS2 sheet oriented in the (0, 0, 1) direction and one MoSe2 sheet oriented in the (0, 0, 1) direction. In the MoS2 sheet, Mo4+ is bonded to six equivalent S2- atoms to form distorted edge-sharing MoS6 pentagonal pyramids. All Mo–S bond lengths are 2.43 Å. S2- is bonded in a 3-coordinate geometry to three equivalent Mo4+ atoms. In the MoSe2 sheet, Mo4+ is bonded to six equivalent Se2- atoms to form distorted edge-sharing MoSe6 pentagonal pyramids. All Mo–Se bond lengths are 2.53 Å. Se2- is bonded in a 3-coordinate geometry to three equivalent Mo4+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on MoSeS by Materials Project

MoSSe is Molybdenite-derived structured and crystallizes in the trigonal P-3m1 space group. The structure is two-dimensional and consists of two MoS2 sheets oriented in the (0, 0, 1) direction and two MoSe2 sheets oriented in the (0, 0, 1) direction. In each MoS2 sheet, Mo4+ is bonded to six equivalent S2- atoms to form distorted edge-sharing MoS6 pentagonal pyramids. All Mo–S bond lengths are 2.43 Å. S2- is bonded in a 3-coordinate geometry to three equivalent Mo4+ atoms. In each MoSe2 sheet, Mo4+ is bonded to six equivalent Se2- atoms to form distorted edge-sharing MoSe6 pentagonal pyramids. All Mo–Se bond lengths are 2.53 Å. Se2- is bonded in a 3-coordinate geometry to three equivalent Mo4+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Charge Transfer Dynamics in MoSe 2 /hBN/WSe 2 Heterostructures

Ultrafast charge transfer processes provide a facile way to create interlayer excitons in directly contacted transition metal dichalcogenide (TMD) layers. More sophisticated heterostructures composed of TMD/hBN/TMD enable new ways to control interlayer exciton properties and achieve novel exciton phenomena, such as exciton insulators and condensates, where longer lifetimes are desired. In this work, we experimentally study the charge transfer dynamics in a heterostructure composed of a 1 nm thick hBN spacer between MoSe 2 and WSe 2 monolayers. We observe the hole transfer from MoSe 2 to WSe 2 through the hBN barrier with a time constant of 500 ps, which is over 3 orders of magnitude slower than that between TMD layers without a spacer. Furthermore, we observe strong competition between the interlayer charge transfer and intralayer exciton–exciton annihilation processes at high excitation densities. Here, our work opens possibilities to understand charge transfer pathways in TMD/hBN/TMD heterostructures for the efficient generation and control of interlayer excitons.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on MoSeS by Materials Project

MoSSe is Molybdenite-derived structured and crystallizes in the trigonal P3m1 space group. The structure is two-dimensional and consists of one MoS2 sheet oriented in the (0, 0, 1) direction and one MoSe2 sheet oriented in the (0, 0, 1) direction. In the MoS2 sheet, Mo4+ is bonded to six S2- atoms to form distorted edge-sharing MoS6 pentagonal pyramids. All Mo–S bond lengths are 2.43 Å. There are two inequivalent S2- sites. In the first S2- site, S2- is bonded in a distorted T-shaped geometry to three equivalent Mo4+ atoms. In the second S2- site, S2- is bonded in a 3-coordinate geometry to three equivalent Mo4+ atoms. In the MoSe2 sheet, Mo4+ is bonded to six equivalent Se2- atoms to form distorted edge-sharing MoSe6 pentagonal pyramids. All Mo–Se bond lengths are 2.53 Å. Se2- is bonded in a 3-coordinate geometry to three equivalent Mo4+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on MoSeS by Materials Project

MoSSe is Molybdenite-derived structured and crystallizes in the trigonal P3m1 space group. The structure is two-dimensional and consists of two MoS2 sheets oriented in the (0, 0, 1) direction and two MoSe2 sheets oriented in the (0, 0, 1) direction. In each MoS2 sheet, Mo4+ is bonded to six S2- atoms to form distorted edge-sharing MoS6 pentagonal pyramids. All Mo–S bond lengths are 2.43 Å. There are two inequivalent S2- sites. In the first S2- site, S2- is bonded in a distorted T-shaped geometry to three equivalent Mo4+ atoms. In the second S2- site, S2- is bonded in a 3-coordinate geometry to three equivalent Mo4+ atoms. In each MoSe2 sheet, Mo4+ is bonded to six equivalent Se2- atoms to form distorted edge-sharing MoSe6 pentagonal pyramids. All Mo–Se bond lengths are 2.53 Å. Se2- is bonded in a 3-coordinate geometry to three equivalent Mo4+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on MoSeS by Materials Project

MoSSe is Molybdenite-derived structured and crystallizes in the trigonal P3m1 space group. The structure is two-dimensional and consists of two MoS2 sheets oriented in the (0, 0, 1) direction and two MoSe2 sheets oriented in the (0, 0, 1) direction. In each MoS2 sheet, Mo4+ is bonded to six S2- atoms to form distorted edge-sharing MoS6 pentagonal pyramids. All Mo–S bond lengths are 2.43 Å. There are two inequivalent S2- sites. In the first S2- site, S2- is bonded in a distorted T-shaped geometry to three equivalent Mo4+ atoms. In the second S2- site, S2- is bonded in a 3-coordinate geometry to three equivalent Mo4+ atoms. In each MoSe2 sheet, Mo4+ is bonded to six equivalent Se2- atoms to form distorted edge-sharing MoSe6 pentagonal pyramids. All Mo–Se bond lengths are 2.53 Å. Se2- is bonded in a 3-coordinate geometry to three equivalent Mo4+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on MoSeS by Materials Project

MoSSe is Molybdenite-derived structured and crystallizes in the trigonal P-3m1 space group. The structure is two-dimensional and consists of two MoS2 sheets oriented in the (0, 0, 1) direction and two MoSe2 sheets oriented in the (0, 0, 1) direction. In each MoS2 sheet, Mo4+ is bonded to six S2- atoms to form distorted edge-sharing MoS6 pentagonal pyramids. All Mo–S bond lengths are 2.43 Å. There are two inequivalent S2- sites. In the first S2- site, S2- is bonded in a distorted T-shaped geometry to three equivalent Mo4+ atoms. In the second S2- site, S2- is bonded in a 3-coordinate geometry to three equivalent Mo4+ atoms. In each MoSe2 sheet, Mo4+ is bonded to six equivalent Se2- atoms to form distorted edge-sharing MoSe6 pentagonal pyramids. All Mo–Se bond lengths are 2.53 Å. Se2- is bonded in a 3-coordinate geometry to three equivalent Mo4+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Salt-Assisted 2H-to-1T' Phase Transformation of Transition Metal Dichalcogenides [plus supplemental information]

Phase engineering of nanomaterials (PEN) has demonstrated great potential in the fields of catalysis, electronics, energy storage and conversion, and condensed matter physics. Recently, transition metal dichalcogenides (TMDs) with unconventional metastable phases (e.g., 1T and 1T') have attracted increasing research interest due to their unique and appealing physicochemical properties. However, there is still a lack of a simple, universal, and controlled method for the preparation of large-scale and high-purity unconventional-phase TMD crystals, restricting their further fundamental study and practical applications. Here, a facile, one-step salt-assisted general strategy is reported for the controlled phase transformation of commercially available TMDs with conventional 2H phase, yielding a large amount of metastable 1T'-phase TMDs, including WS 2 , WSe 2 , MoS 2 , and MoSe 2 . It is found that the easily accessible metal salts, such as K 2 C 2 O 4 ·H 2 O, K 2 CO 3 , Na 2 CO 3 , Rb 2 CO 3 , Cs 2 CO 3 , KHCO 3 , NaHCO 3 , and NaC 2 O 4 , can be used to assist the 2H-to-1T' phase transformation, greatly simplifying the synthetic process for producing metastable 1T'-TMDs. Importantly, this method can also be used to prepare 1T'-TMD alloys, such as 1T'-WS 2x Se 2(1–x) . We report this newly developed strategy is robust and highly effective, which can also be used for the phase engineering of other materials with various polymorphs.

1T′ phase↗
DOE OSTI2023

High-throughput ab initio design of atomic interfaces using InterMatch

Forming a hetero-interface is a materials-design strategy that can access an astronomically large phase space. However, the immense phase space necessitates a high-throughput approach for an optimal interface design. Here we introduce a high-throughput computational framework, InterMatch, for efficiently predicting charge transfer, strain, and superlattice structure of an interface by leveraging the databases of individual bulk materials. Specifically, the algorithm reads in the lattice vectors, density of states, and the stiffness tensors for each material in their isolated form from the Materials Project. From these bulk properties, InterMatch estimates the interfacial properties. We benchmark InterMatch predictions for the charge transfer against experimental measurements and supercell density-functional theory calculations. We then use InterMatch to predict promising interface candidates for doping transition metal dichalcogenide MoSe 2 . Finally, we explain experimental observation of factor of 10 variation in the supercell periodicity within a few microns in graphene/α-RuCl 3 by exploring low energy superlattice structures as a function of twist angle using InterMatch. We anticipate our open-source InterMatch algorithm accelerating and guiding ever-growing interfacial design efforts. Moreover, the interface database resulting from the InterMatch searches presented in this paper can be readily accessed online.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Tuning bandgap and energy stability of Organic-Inorganic halide perovskites through surface engineering

Organohalide perovskite with a variety of surface structures and morphologies have shown promising potential owing to the choice of the type of heterostructure dependent stability. We systematically investigate and discuss the impact of 2-dimensional molybdenum-disulphide (MoS 2 ), molybdenum-diselenide (MoSe 2 ), tungsten-disulphide (WS 2 ), tungsten-diselenide (WSe 2 ), boron-nitiride (BN) and graphene monolayers on bandgap and energy stability of organic–inorganic halide perovskites. We found that MAPbI 3 deposited on BN-ML shows room temperature stability (-25 meV ~ 300 K) with an optimal bandgap of ~ 1.68 eV. The calculated absorption coefficient also lies in the visible-light range with a maximum of 4.9 × 10 4 cm –1 achieved at 2.8 eV photon energy. Furthermore, on the basis of our calculations, we suggest that the encapsulation of an organic–inorganic halide perovskite monolayers by semiconducting monolayers potentially provides greater flexibility for tuning the energy stability and the bandgap.

36 MATERIALS SCIENCE↗
NASA NTRS1994

Flank solar wind interaction

In this report we will summarize the results of the work performed under the 'Flank Solar Wind Interaction' investigation in support of NASA's Space Physics Guest Investigator Program. While this investigation was focused on the interaction of the Earth's magnetosphere with the solar wind as observed by instruments on the International Sun-Earth Explorer (ISEE) 3 spacecraft, it also represents the culmination of decades of research performed by scientists at TRW on the rich phenomenology of collisionless shocks in space.

Moses, Stewart L.↗