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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 OSTI2019

Interconnected Vertically Stacked 2D-MoS2 for Ultrastable Cycling of Rechargeable Li-Ion Battery

2D layer structured material is often high-capacity ionic storage material with fast ionic transport within the layers. This appears to be the case for non-conversion layer structure, such as graphite. However, this is not the case for conversion-type layered structure such as transition metal sulfide, in which localized congestion of ionic species adjacent to the surface will induce localized conversion, leading to the blocking of the fast diffusion channels and fast capacity fading, which therefore constitutes one of the critical barriers for the application of transition metal sulfide layered structure. In this work, we report the tackling of this critical barrier through nanoscale engineering. We discover that vertically-stacked 2D-MoS2 can dramatically enhance the cycling stability. Atomic level in-situ TEM observation reveals that the MoS2 nanocakes assembled with tangling (100)-terminated nanosheets offer abundant open channels for Li+ insertion through the (100) surface, featuring an enhanced cyclability performance for over 200 cycle with a capacity retention of 90%. In contrast, (001)-terminated MoS2 nanoflowers only retains 10% of original capacity after 50 cycles. The present work demonstrates a general principle and opens a new route of crystallographic design to enhance electrochemical performance for assembling 2D materials for energy storage.

Sun, Congli↗
DOE OSTI2021

Electronic structure modulation of MoS2 by substitutional Se incorporation and interfacial MoO3 hybridization: Implications of Fermi engineering for electrocatalytic hydrogen evolution and oxygen evolution

The design of earth-abundant electrocatalysts that can facilitate water splitting at low overpotentials, provide high current densities, and enable prolonged operational lifetimes is central to the production of sustainable fuels. The distinctive atomistic and electronic structure characteristics of the edges of MoS2 imbue high reactivity toward the hydrogen evolution reaction. MoS2 is nevertheless characterized by significantly high overpotentials as compared to platinum. Here, we demonstrate that modulation of the electronic structure of MoS2 through interfacial hybridization with MoO3 and alloying of selenium on the anion sublattice allows for systematic lowering of the conduction band edge and raising of the valence band edge, respectively. The former promotes enhanced electrocatalytic activity toward hydrogen evolution, whereas the latter promotes enhanced activity toward the oxygen evolution reaction. Such alloyed heterostructures prepared by sol-gel reactions and hydrothermal selenization expose a high density of edge sites. The alloyed heterostructures exhibit low overpotential, high current density, high turnover frequency, and prolonged operational lifetime. The mechanistic origins of catalytic activity have been established based on electronic structure calculations and x-ray absorption and emission spectroscopy probes of electronic structure, which suggest that interfacial hybridization at the MoO3 interface yields low-lying conduction band states that facilitate hydrogen adsorption. In contrast, shallow Se 4p-derived states give rise to a raised effective valence band maximum, which facilitates adsorption of oxygen intermediates and engenders a low overpotential for the oxygen evolution reaction. The findings illustrate the use of electronic structure modulation through interfacial hybridization and alloying to systematically improve electrocatalytic activity.

Parija, Abhishek↗
NASA NTRS1972

Magnetic field effects on superconductivity in alkali metal intercalates of MoS2

The effects of a magnetic field on the superconducting transition in MoS2 intercalated with potassium and sodium were studied. It was found that the potassium intercalated MoS2 has better properties in a magnetic field. In zero magnetic field the transition to superconductivity begins near 6.4 K. Diagrams of the basic circuitry for superconducting transition studies, and charts showing critical magnetic field versus critical temperature for the intercalated MoS2 are included.

Woollam, J. A.↗
NASA NTRS1986

Towards an optimised sputtered MoS2 lubricant film

It is shown that the tribological quality of MoS2 lubricant films formed by magnetron sputtering is determined by the choice of sputtering conditions. By selecting the appropriate conditions, films of extremely high lubricity and endurance (in vacuum), which are well suited to many space applications, are obtained. Such MoS2 films, when applied to precision ball hearings, give rise to the lowest torques (for the given test conditions) yet seen in our laboratory. While a remarkably good performance is obtained in vacuum, tests in air show a marked deterioration in lubricating qualities. It is demonstrated that this is attributable to the adsorption of water vapor on MoS2 surfaces and that the degree of deterioration is related to the partial pressure of water vapor present. Analysis of results indicates that the factors relevant to obtaining optimum films are deposition rate and film composition.

Roberts, E. W.↗
DOE OSTI2020

Materials Data on MoS2 by Materials Project

MoS2 is Molybdenite-like structured and crystallizes in the trigonal R3m space group. The structure is two-dimensional and consists of three MoS2 sheets oriented in the (0, 0, 1) direction. Mo4+ is bonded to six equivalent S2- atoms to form distorted edge-sharing MoS6 pentagonal pyramids. All Mo–S bond lengths are 2.42 Å. S2- is bonded in a 3-coordinate geometry to three equivalent Mo4+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on MoS2 by Materials Project

MoS2 is Molybdenite structured and crystallizes in the hexagonal P6_3/mmc space group. The structure is two-dimensional and consists of two MoS2 sheets oriented in the (0, 0, 1) direction. Mo4+ is bonded to six equivalent S2- atoms to form distorted edge-sharing MoS6 pentagonal pyramids. All Mo–S bond lengths are 2.42 Å. S2- is bonded in a 3-coordinate geometry to three equivalent Mo4+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on MoS2 by Materials Project

MoS2 is trigonal omega-like structured and crystallizes in the monoclinic C2/m space group. The structure is two-dimensional and consists of one MoS2 sheet oriented in the (0, 0, 1) direction. Mo4+ is bonded to six equivalent S2- atoms to form edge-sharing MoS6 octahedra. All Mo–S bond lengths are 2.44 Å. S2- is bonded in a 3-coordinate geometry to three equivalent Mo4+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Materials Data on MoS2 by Materials Project

MoS2 crystallizes in the orthorhombic Pmmn space group. The structure is one-dimensional and consists of two MoS2 ribbons oriented in the (1, 0, 0) direction. there are eight inequivalent Mo4+ sites. In the first Mo4+ site, Mo4+ is bonded to six equivalent S2- atoms to form distorted edge-sharing MoS6 pentagonal pyramids. There are four shorter (2.41 Å) and two longer (2.42 Å) Mo–S bond lengths. In the second Mo4+ site, Mo4+ is bonded to six S2- atoms to form distorted edge-sharing MoS6 pentagonal pyramids. There are four shorter (2.41 Å) and two longer (2.42 Å) Mo–S bond lengths. In the third Mo4+ site, Mo4+ is bonded to six S2- atoms to form distorted edge-sharing MoS6 pentagonal pyramids. There are four shorter (2.41 Å) and two longer (2.42 Å) Mo–S bond lengths. In the fourth Mo4+ site, Mo4+ is bonded to six S2- atoms to form distorted edge-sharing MoS6 pentagonal pyramids. There are four shorter (2.41 Å) and two longer (2.42 Å) Mo–S bond lengths. In the fifth Mo4+ site, Mo4+ is bonded to six S2- atoms to form distorted edge-sharing MoS6 pentagonal pyramids. There are four shorter (2.41 Å) and two longer (2.42 Å) Mo–S bond lengths. In the sixth Mo4+ site, Mo4+ is bonded to six S2- atoms to form distorted edge-sharing MoS6 pentagonal pyramids. There are four shorter (2.42 Å) and two longer (2.47 Å) Mo–S bond lengths. In the seventh Mo4+ site, Mo4+ is bonded in a distorted square co-planar geometry to four equivalent S2- atoms. All Mo–S bond lengths are 2.39 Å. In the eighth Mo4+ site, Mo4+ is bonded to six S2- atoms to form distorted edge-sharing MoS6 pentagonal pyramids. There are four shorter (2.39 Å) and two longer (2.42 Å) Mo–S bond lengths. There are eight inequivalent S2- sites. In the first S2- site, S2- is bonded in a 3-coordinate geometry to three Mo4+ atoms. In the second S2- site, S2- is bonded in a 3-coordinate geometry to three Mo4+ atoms. The S–Mo bond length is 2.42 Å. In the third S2- site, S2- is bonded in an L-shaped geometry to two equivalent Mo4+ atoms. In the fourth S2- site, S2- is bonded in a 3-coordinate geometry to three Mo4+ atoms. In the fifth S2- site, S2- is bonded in a 3-coordinate geometry to three Mo4+ atoms. In the sixth S2- site, S2- is bonded in a 3-coordinate geometry to three Mo4+ atoms. In the seventh S2- site, S2- is bonded in a 3-coordinate geometry to three Mo4+ atoms. In the eighth S2- site, S2- is bonded in a 3-coordinate geometry to three Mo4+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on MoS2 by Materials Project

MoS2 is Molybdenite-like structured and crystallizes in the hexagonal P6_3/mmc space group. The structure is two-dimensional and consists of two MoS2 sheets oriented in the (0, 0, 1) direction. Mo4+ is bonded to six equivalent S2- atoms to form distorted edge-sharing MoS6 pentagonal pyramids. All Mo–S bond lengths are 2.42 Å. S2- is bonded in a 3-coordinate geometry to three equivalent Mo4+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on MoS2 by Materials Project

MoS2 is Molybdenite-like structured and crystallizes in the hexagonal P-6m2 space group. The structure is two-dimensional and consists of one MoS2 sheet oriented in the (0, 0, 1) direction. Mo4+ is bonded to six equivalent S2- atoms to form distorted edge-sharing MoS6 pentagonal pyramids. All Mo–S bond lengths are 2.42 Å. S2- is bonded in a 3-coordinate geometry to three equivalent Mo4+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on MoS2 by Materials Project

MoS2 is Molybdenite-like 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. Mo4+ is bonded to six equivalent S2- atoms to form distorted edge-sharing MoS6 pentagonal pyramids. All Mo–S bond lengths are 2.42 Å. S2- is bonded in a 3-coordinate geometry to three equivalent Mo4+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on MoS2 by Materials Project

MoS2 is Molybdenite-like structured and crystallizes in the hexagonal P-6m2 space group. The structure is two-dimensional and consists of three MoS2 sheets oriented in the (0, 0, 1) direction. Mo4+ is bonded to six equivalent S2- atoms to form distorted edge-sharing MoS6 pentagonal pyramids. All Mo–S bond lengths are 2.42 Å. S2- is bonded in a 3-coordinate geometry to three equivalent Mo4+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on MoS2 by Materials Project

MoS2 is Molybdenite-like structured and crystallizes in the trigonal P-3m1 space group. The structure is two-dimensional and consists of four MoS2 sheets oriented in the (0, 0, 1) direction. Mo4+ is bonded to six equivalent S2- atoms to form distorted edge-sharing MoS6 pentagonal pyramids. All Mo–S bond lengths are 2.42 Å. S2- is bonded in a 3-coordinate geometry to three equivalent Mo4+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Materials Data on Al(MoS2)4 by Materials Project

Al(MoS2)4 crystallizes in the monoclinic Cm space group. The structure is two-dimensional and consists of one Al(MoS2)4 sheet oriented in the (2, 0, -1) direction. there are three inequivalent Mo+3.25+ sites. In the first Mo+3.25+ site, Mo+3.25+ is bonded to four S2- atoms to form edge-sharing MoS4 tetrahedra. There are a spread of Mo–S bond distances ranging from 2.15–2.36 Å. In the second Mo+3.25+ site, Mo+3.25+ is bonded to four S2- atoms to form a mixture of corner and edge-sharing MoS4 tetrahedra. There are a spread of Mo–S bond distances ranging from 2.29–2.35 Å. In the third Mo+3.25+ site, Mo+3.25+ is bonded to four S2- atoms to form a mixture of corner and edge-sharing MoS4 trigonal pyramids. There are a spread of Mo–S bond distances ranging from 2.28–2.38 Å. Al3+ is bonded in a distorted trigonal non-coplanar geometry to three S2- atoms. All Al–S bond lengths are 2.25 Å. There are six inequivalent S2- sites. In the first S2- site, S2- is bonded in a distorted L-shaped geometry to one Mo+3.25+ and one Al3+ atom. In the second S2- site, S2- is bonded in a 3-coordinate geometry to three Mo+3.25+ atoms. In the third S2- site, S2- is bonded in a 3-coordinate geometry to three Mo+3.25+ atoms. In the fourth S2- site, S2- is bonded in a trigonal planar geometry to three Mo+3.25+ atoms. In the fifth S2- site, S2- is bonded in a single-bond geometry to one Mo+3.25+ atom. In the sixth S2- site, S2- is bonded in a distorted L-shaped geometry to one Mo+3.25+ and one Al3+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Experimental and modeling study of 1/ f noise in multilayer MoS2 and MoSe2 field-effect transistors

In field-effect transistors (FETs) with two-dimensional (2D) transition metal dichalcogenide channels, the dependence of field-effect mobility on atomic layer thickness has been studied and interpreted in terms of interface scattering and interlayer coupling resistance (Rint). However, a model for 1/f noise, such as in MoS2 and in MoSe2 FETs, for various contact metals and layer number thicknesses has not been reported. In this work, we have experimentally studied current–voltage and 1/f noise on MoS2 and MoSe2 FETs with source and drain contacts of high and low work function metals to understand both the mobility and the noise behavior. We have developed a noise model incorporating layer number dependent Hooge parameters and Rint. The noise and mobility models utilize screening lengths for charge, mobility, and Hooge parameter to describe the variation of these quantities with a layer number. Using our single model topology with appropriate fitting parameters for each material and each contact metal, the model captures the experimentally observed layer thickness dependence of the Hooge parameter. Our noise analysis is fully comprehensive and, hence, could be applied to any 2D layered systems.

Kwon, Jiseok↗
DOE OSTI2025

Exciton thermalization dynamics in monolayer MoS2: A first-principles Boltzmann equation study

Understanding exciton thermalization is critical for optimizing optoelectronic and photocatalytic processes in many materials. However, it is hard to access the dynamics of such processes experimentally, especially on systems such as monolayer transition metal dichalcogenides, where various low-energy excitations pathways can compete for exciton thermalization. Here, we study exciton dynamics due to exciton-phonon scattering in monolayer MoS2 from a first-principles, interacting Green's function approach, to obtain the relaxation and thermalization of low-energy excitons following different initial excitations at different temperatures. We find that the thermalization occurs on a picosecond time scale at 300 K but can increase by an order of magnitude at 100 K. The long total thermalization time, owing to the nature of its excitonic band structure, is dominated by slow spin-flip scattering processes in monolayer MoS2. In contrast, thermalization of excitons in individual spin-aligned and spin-anti-aligned channels can be achieved within a few hundred fs when exciting higher-energy excitons. We further simulate the intensity spectrum of time-resolved angle-resolved photoemission spectroscopy experiments and anticipate that such calculations may serve as a map to correlate spectroscopic signatures with microscopic exciton dynamics.

Chan, Yang-hao↗
DOE OSTI2024

Comparing Exciton-Polariton Couplings in Two-Dimensional MoS2 Cavities

Exciton-polaritons (EPs) are an emerging approach to achieve strong light-matter coupling and robust quantum phenomena, with application to areas such as photonic neuromorphic computing for instance reservoir computing. 2D transition metal dichalcogenides (TMDs) are promising candidates to host EPs due to their potential for strong coupling as evidenced by large Rabi splitting energies, which in the case of few-layer MoS2 has been demonstrated to reach 293 meV when coupled to the C exciton, placing it in the ultrastrong coupling regime, at room temperature. Here we examine how the Rabi splitting of CVD-grown monolayer MoS2 in a cavity can be optimized by tuning two variables: cavity geometry (thickness of silver and dielectric spacers) and the targeted exciton for coupling (A at about 1.9 eV, B at about 2.06 eV, or C at about 2.9 eV). With the cavity geometry, there is a tradeoff between optical field confinement and transmission. With the targeted exciton, there may be a tradeoff between Rabi splitting and lifetime. Transfer matrix simulations are used to inform how thick the cavity layers need to be, and at what angle measurements should be performed, to achieve Rabi splitting at a certain exciton energy. Experimentally, the Rabi splitting is measured by placing the cavity at a specified angle and measuring the optical reflectance and transmittance. By fitting the data, we find Rabi splittings of 124 meV, 194 meV, and 288 meV for the A, B, and C excitons, respectively, which places them in the strong, and on the edge of the ultrastrong, coupling regime.

exciton-polaritons↗
DOE OSTI2019

Understanding Phase Stability of Metallic 1T-MoS2 Anodes for Sodium-Ion Batteries

We discuss metallic 1T-MoS2 as an anode material for sodium-ion batteries (SIBs). In situ Raman is used to investigate the stability of metallic MoS2 during the charging and discharging processes. Parallel first-principles computations are used to gain insight into the experimental observations, including the measured conductivities and the high capacity of the anode.

Lane, Christopher (ORCID:0000000329459352)↗