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At least 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Materials Data on NaIn(MoSe)6 by Materials Project

NaIn(MoSe)6 crystallizes in the hexagonal P-6 space group. The structure is three-dimensional. Na is bonded in a trigonal planar geometry to three equivalent Se atoms. All Na–Se bond lengths are 2.96 Å. There are two inequivalent Mo sites. In the first Mo site, Mo is bonded in a distorted see-saw-like geometry to six Mo and four Se atoms. There are a spread of Mo–Mo bond distances ranging from 2.67–2.74 Å. There are a spread of Mo–Se bond distances ranging from 2.63–2.71 Å. In the second Mo site, Mo is bonded in a distorted see-saw-like geometry to six Mo and four Se atoms. Both Mo–Mo bond lengths are 2.67 Å. There are a spread of Mo–Se bond distances ranging from 2.63–2.72 Å. In is bonded in a trigonal planar geometry to three equivalent Se atoms. All In–Se bond lengths are 3.01 Å. There are two inequivalent Se sites. In the first Se site, Se is bonded in a 1-coordinate geometry to one Na and four Mo atoms. In the second Se site, Se is bonded in a 5-coordinate geometry to four Mo and one In atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on MoSe by Materials Project

MoSe is Tungsten Carbide structured and crystallizes in the hexagonal P-6m2 space group. The structure is three-dimensional. Mo2+ is bonded to six equivalent Se2- atoms to form a mixture of distorted edge, corner, and face-sharing MoSe6 pentagonal pyramids. All Mo–Se bond lengths are 2.62 Å. Se2- is bonded in a 6-coordinate geometry to six equivalent Mo2+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on In(MoSe)3 by Materials Project

In(MoSe)3 crystallizes in the monoclinic P2_1/m space group. The structure is three-dimensional. there are three inequivalent Mo sites. In the first Mo site, Mo is bonded in a distorted see-saw-like geometry to six Mo and four Se atoms. There are two shorter (2.68 Å) and four longer (2.74 Å) Mo–Mo bond lengths. There are a spread of Mo–Se bond distances ranging from 2.64–2.71 Å. In the second Mo site, Mo is bonded in a distorted see-saw-like geometry to six Mo and four Se atoms. There are one shorter (2.68 Å) and two longer (2.74 Å) Mo–Mo bond lengths. There are a spread of Mo–Se bond distances ranging from 2.64–2.71 Å. In the third Mo site, Mo is bonded in a distorted see-saw-like geometry to six Mo and four Se atoms. There are a spread of Mo–Se bond distances ranging from 2.64–2.71 Å. In is bonded in a trigonal planar geometry to three Se atoms. All In–Se bond lengths are 3.09 Å. There are two inequivalent Se sites. In the first Se site, Se is bonded in a 5-coordinate geometry to four Mo and one In atom. In the second Se site, Se is bonded in a 5-coordinate geometry to four Mo and one In atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on K(MoSe)3 by Materials Project

K(MoSe)3 crystallizes in the hexagonal P6_3/m space group. The structure is three-dimensional. K is bonded in a 9-coordinate geometry to nine equivalent Se atoms. There are three shorter (3.50 Å) and six longer (3.53 Å) K–Se bond lengths. Mo is bonded in a distorted see-saw-like geometry to four equivalent Se atoms. There are two shorter (2.65 Å) and two longer (2.73 Å) Mo–Se bond lengths. Se is bonded to three equivalent K and four equivalent Mo atoms to form a mixture of distorted edge, face, and corner-sharing SeK3Mo4 hexagonal pyramids.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ba(MoSe)3 by Materials Project

Ba(MoSe)3 crystallizes in the monoclinic P2_1/m space group. The structure is three-dimensional. Ba is bonded in a 9-coordinate geometry to nine Se atoms. There are a spread of Ba–Se bond distances ranging from 3.43–3.49 Å. There are three inequivalent Mo sites. In the first Mo site, Mo is bonded in a distorted see-saw-like geometry to four Se atoms. There are a spread of Mo–Se bond distances ranging from 2.68–2.75 Å. In the second Mo site, Mo is bonded in a distorted see-saw-like geometry to four Se atoms. There are a spread of Mo–Se bond distances ranging from 2.68–2.75 Å. In the third Mo site, Mo is bonded in a distorted see-saw-like geometry to four Se atoms. There are two shorter (2.68 Å) and two longer (2.74 Å) Mo–Se bond lengths. There are three inequivalent Se sites. In the first Se site, Se is bonded to three equivalent Ba and four Mo atoms to form a mixture of distorted corner, edge, and face-sharing SeBa3Mo4 hexagonal pyramids. In the second Se site, Se is bonded to three equivalent Ba and four Mo atoms to form a mixture of distorted corner, edge, and face-sharing SeBa3Mo4 hexagonal pyramids. In the third Se site, Se is bonded to three equivalent Ba and four Mo atoms to form a mixture of distorted corner, edge, and face-sharing SeBa3Mo4 hexagonal pyramids.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on LiIn(MoSe)6 by Materials Project

LiIn(MoSe)6 crystallizes in the hexagonal P-6 space group. The structure is three-dimensional. Li is bonded in a trigonal planar geometry to three equivalent Se atoms. All Li–Se bond lengths are 2.80 Å. There are two inequivalent Mo sites. In the first Mo site, Mo is bonded in a distorted see-saw-like geometry to six Mo and four Se atoms. There are a spread of Mo–Mo bond distances ranging from 2.67–2.75 Å. There are a spread of Mo–Se bond distances ranging from 2.63–2.70 Å. In the second Mo site, Mo is bonded in a distorted see-saw-like geometry to six Mo and four Se atoms. Both Mo–Mo bond lengths are 2.68 Å. There are a spread of Mo–Se bond distances ranging from 2.61–2.73 Å. In is bonded in a trigonal planar geometry to three equivalent Se atoms. All In–Se bond lengths are 2.94 Å. There are two inequivalent Se sites. In the first Se site, Se is bonded in a 1-coordinate geometry to one Li and four Mo atoms. In the second Se site, Se is bonded in a 5-coordinate geometry to four Mo and one In atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Cs(MoSe)3 by Materials Project

Cs(MoSe)3 crystallizes in the monoclinic P2_1/m space group. The structure is three-dimensional. Cs is bonded in a 9-coordinate geometry to nine Se atoms. There are a spread of Cs–Se bond distances ranging from 3.81–3.92 Å. There are three inequivalent Mo sites. In the first Mo site, Mo is bonded in a distorted see-saw-like geometry to four Se atoms. There are a spread of Mo–Se bond distances ranging from 2.63–2.72 Å. In the second Mo site, Mo is bonded in a distorted see-saw-like geometry to four Se atoms. There are a spread of Mo–Se bond distances ranging from 2.63–2.72 Å. In the third Mo site, Mo is bonded in a distorted see-saw-like geometry to four Se atoms. There are a spread of Mo–Se bond distances ranging from 2.63–2.72 Å. There are three inequivalent Se sites. In the first Se site, Se is bonded in a 7-coordinate geometry to three equivalent Cs and four Mo atoms. In the second Se site, Se is bonded in a 7-coordinate geometry to three equivalent Cs and four Mo atoms. In the third Se site, Se is bonded in a 7-coordinate geometry to three equivalent Cs and four Mo atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Na(MoSe)3 by Materials Project

Na(MoSe)3 crystallizes in the hexagonal P6_3/m space group. The structure is three-dimensional. Na is bonded in a 9-coordinate geometry to nine equivalent Se atoms. There are three shorter (3.26 Å) and six longer (3.44 Å) Na–Se bond lengths. Mo is bonded in a distorted see-saw-like geometry to four equivalent Se atoms. There are a spread of Mo–Se bond distances ranging from 2.64–2.72 Å. Se is bonded in a 7-coordinate geometry to three equivalent Na and four equivalent Mo atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Site-Controlled Quantum Emitters in Monolayer MoSe 2

Atomically thin semiconductors provide a highly attractive platform for quantum emitters (QEs): They can be combined with arbitrary substrates, can be spatially aligned with photonic structures, and can be electrically driven. All QEs reported to date in these materials have, however, relied on nominally spin-forbidden transitions, with radiative rates falling substantially below those of other solid-state QE systems. In this work, we employ strain confinement in monolayer MoSe 2 to produce engineered QEs, as confirmed in photon antibunching measurements. We discuss spin-allowed versus spin-forbidden transitions based on magneto- and time-resolved photoluminescence measurements. We calculate a radiative rate for spin-allowed quantum emission greater than 1 ns –1 , which exceeds reported radiative rates of WSe 2 QEs by 2 orders of magnitude.

2D materials↗
DOE OSTI2020

Indirect Excitons and Trions in MoSe 2 /WSe 2 van der Waals Heterostructures

Indirect excitons (IX) in semiconductor heterostructures are bosons, which can cool below the temperature of quantum degeneracy and can be effectively controlled by voltage and light. In this work, IX quantum Bose gases and IX devices were explored in GaAs heterostructures where an IX range of existence is limited to low temperatures due to low IX binding energies. IXs in van der Waals transition-metal dichalcogenide (TMD) heterostructures are characterized by large binding energies giving the opportunity for exploring excitonic quantum gases and for creating excitonic devices at high temperatures. TMD heterostructures also offer a new platform for studying single-exciton phenomena and few-particle complexes. In this work, we present studies of IXs in MoSe 2 /WSe 2 heterostructures and report on two IX luminescence lines whose energy splitting and temperature dependence identify them as neutral and charged IXs. The experimentally found binding energy of the indirect charged excitons, that is, indirect trions, is close to the calculated binding energy of 28 meV for negative indirect trions in TMD heterostructures. We also report on the realization of IXs with a luminescence line width reaching 4 meV at low temperatures. An enhancement of IX luminescence intensity and the narrow line width are observed in localized spots.

2D materials↗
DOE OSTI2025

Room-temperature valley-selective emission in Si-MoSe 2 heterostructures enabled by high-quality-factor chiroptical cavities

Transition metal dichalcogenides possess valley pseudospin, enabling coupling between photon spin and electron spin for classical and quantum information processing. However, rapid valley-dephasing processes have impeded the development of scalable, high-performance valleytronic devices operating at room temperature. Here we demonstrate that a chiral resonant metasurface can enable room-temperature valley-selective emission in MoSe 2 monolayers independent of excitation polarization. This platform provides circular eigen-polarization states with a high quality factor (Q-factor) and strong chiral near-field enhancement. The fabricated Si chiral metasurfaces exhibit chiroptical resonances with Q-factors up to 450 at visible wavelengths. We reveal degrees of circular polarization (DOP) reaching a record high of 0.5 at room temperature. Our measurements show that the high DOP can be attributed to the significantly increased chiroptical local density of states, which enhances valley-specific radiative transition rates by a factor of ~13. Our work could facilitate the development of ultracompact chiral classical and quantum light sources.

42 ENGINEERING↗
DOE OSTI2022

Imaging gate-tunable Tomonaga–Luttinger liquids in 1H-MoSe 2 mirror twin boundaries

One-dimensional electron systems exhibit fundamentally different properties than higher-dimensional systems. For example, electron-electron interactions in one-dimensional electron systems have been predicted to induce Tomonaga-Luttinger liquid behaviour. Naturally occurring grain boundaries in single-layer transition metal dichalcogenides exhibit one-dimensional conducting channels that have been proposed to host Tomonaga-Luttinger liquids, but charge density wave physics has also been suggested to explain their behaviour. Clear identification of the electronic ground state of this system has been hampered by an inability to electrostatically gate such boundaries and tune their charge carrier concentration. Here we present a scanning tunnelling microscopy and spectroscopy study of gate-tunable mirror twin boundaries in single-layer 1H-MoSe 2 devices. Gating enables scanning tunnelling microscopy and spectroscopy for different mirror twin boundary electron densities, thus allowing precise characterization of electron-electron interaction effects. Visualization of the resulting mirror twin boundary electronic structure allows unambiguous identification of collective density wave excitations having two velocities, in quantitative agreement with the spin-charge separation predicted by finite-length Tomonaga-Luttinger liquid theory.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Moiré trions in MoSe 2 /WSe 2 heterobilayers

Transition metal dichalcogenide moiré bilayers with spatially periodic potentials have emerged as a highly tunable platform for studying both electronic and excitonic phenomena. The power of these systems lies in the combination of strong Coulomb interactions with the capability of controlling the charge number in a moiré potential trap. Electronically, exotic charge orders at both integer and fractional fillings have been discovered. However, the impact of charging effects on excitons trapped in moiré potentials is poorly understood. Here, we report the observation of moiré trions and their doping-dependent photoluminescence polarization in H-stacked MoSe 2 /WSe 2 heterobilayers. We find that as moiré traps are filled with either electrons or holes, new sets of interlayer exciton photoluminescence peaks with narrow linewidths emerge about 7 meV below the energy of the neutral moiré excitons. Circularly polarized photoluminescence reveals switching from co-circular to cross-circular polarizations as moiré excitons go from being negatively charged and neutral to positively charged. Furthermore, this switching results from the competition between valley-flip and spin-flip energy relaxation pathways of photo-excited electrons during interlayer trion formation. Our results offer a starting point for engineering both bosonic and fermionic many-body effects based on moiré excitons.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Emergence of composite many-body exciton states in WS 2 and MoSe 2 monolayers

When doped with a high density of mobile charge carriers, monolayer transition-metal dichalcogenide (TMD) semiconductors can host new types of composite many-particle exciton states that do not exist in conventional semiconductors. Further, such multiparticle bound states arise when a photoexcited electron-hole pair couples not to just a single Fermi sea that is quantum-mechanically distinguishable (as in the case of conventional charged excitons or trions), but rather couples simultaneously to multiple Fermi seas, each having distinct spin and valley quantum numbers. Composite six-particle “hexciton” states were recently identified in electron-doped $WSe$ $2$ monolayers, but under suitable conditions they should also form in all other members of the monolayer TMD family. Here we present spectroscopic evidence demonstrating the emergence of many-body hexcitons in charge-tunable $WS$ $2$ monolayers (at the A-exciton) and $MoSe$ $2$ monolayers (at the B-exciton). The roles of distinguishability and carrier screening on the stability of hexcitons are discussed.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Phonon-Assisted Intervalley Scattering Determines Ultrafast Exciton Dynamics in MoSe 2 Bilayers

While valleys (energy extrema) are present in all band structures of solids, their preeminent role in determining exciton resonances and dynamics in atomically thin transition metal dichalcogenides (TMDC) is unique. Using two-dimensional coherent electronic spectroscopy, we find that exciton decoherence occurs on a much faster timescale in MoSe 2 bilayers than that in the monolayers. We further identify two population relaxation channels in the bilayer, a coherent and an incoherent one. Our microscopic model reveals that phonon-emission processes facilitate scattering events from the K valley to other lower-energy Γ and Λ valleys in the bilayer. Our combined experimental and theoretical studies unequivocally establish different microscopic mechanisms that determine exciton quantum dynamics in TMDC monolayers and bilayers. Understanding exciton quantum dynamics provides critical guidance to the manipulation of spin-valley degrees of freedom in TMDC bilayers.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2024

Electrical Control and Transport of Tightly Bound Interlayer Excitons in a MoSe 2 /hBN/MoSe 2 Heterostructure

Controlling interlayer excitons in Van der Waals heterostructures holds promise for exploring Bose-Einstein condensates and developing novel optoelectronic applications, such as excitonic integrated circuits. Despite intensive studies, several key fundamental properties of interlayer excitons, such as their binding energies and interactions with charges, remain not well understood. Here we report the formation of momentum-direct interlayer excitons in a high-quality MoSe 2 /hBN/MoSe 2 heterostructure under an electric field, characterized by bright photoluminescence (PL) emission with high quantum yield and a narrow linewidth of less than 4 meV. These interlayer excitons show electrically tunable emission energy spanning ~1⁢8⁢0 meV through the Stark effect, and exhibit a sizable binding energy of ~8⁢1 meV in the intrinsic regime, along with trion binding energies of a few millielectronvolts. Remarkably, we demonstrate the long-range transport of interlayer excitons with a characteristic diffusion length exceeding 1⁢0 μ⁢m, which can be attributed, in part, to their dipolar repulsive interactions. Further, spatially and polarization-resolved spectroscopic studies reveal rich exciton physics in the system, such as valley polarization, local trapping, and the possible existence of dark interlayer excitons. Furthermore, the formation and transport of tightly bound interlayer excitons with narrow linewidth, coupled with the ability to electrically manipulate their properties, open exciting new avenues for exploring quantum many-body physics, including excitonic condensate and superfluidity, and for developing novel optoelectronic devices, such as exciton and photon routers.

2-dimensional systems↗
DOE OSTI2025

Sequential multidimensional heteroepitaxy of chalcogen-sharing 3D ZnSe and 2D MoSe 2 with quasi van der Waals interface engineering

Two-dimensional (2D) materials are emerging as a promising platform for epitaxial growth, largely free from the constraints of lattice constant and thermal expansion coefficient mismatches. Among them, transition metal dichalcogenides (TMDs), known for their superior electrical properties, are ideal for ultrathin semiconductor applications. Their unique epitaxial characteristics enable seamless integration with 3D materials, facilitating the development of gate stacks and heterojunction devices. In this regard, developing a process for growing high-quality 3D epitaxial materials before and after the growth of 2D TMDs and understanding the 2D/3D interface are crucial. This study demonstrates the sequential growth of fully epitaxial ZnSe/MoSe 2 /ZnSe heterostructures using metal-organic chemical vapor deposition. ZnSe and MoSe 2 , sharing chalcogen elements, enable large-area quasi van der Waals epitaxy with sharp interfaces without intermediate phase. Multiscale analysis involving transmission electron microscopy and density functional theory calculation reveals lattice commensurability, van der Waals gaps, termination, and interfacial reconstruction. Understanding these interactions is crucial for advancing multidimensional integration of 2D and 3D materials.

36 MATERIALS SCIENCE↗