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At least 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
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↗
NASA NTRS1985

Spectroscopy of Moses Rock Kimberlite Diatreme

Three types of remote sensing data (Airborne Imaging Spectroscopy (AIS), NS001, Zeiss IR-photographs) were obtained for the Moses Rock kimberlite dike in southern Utah. The goal is to identify and characterize the mantle derived mafic component in such volcanic features. The Zeiss and NS001 images provide information on the regional setting and allow units of the dike to be distinguished from surrounding material. A potential unmapped satellite dike was identified. The AIS data provide characterizing information of the surface composition of the dike. Serpentized olivine-bearing soils are (tentatively) identified from the AIS spectra for a few areas within the dike.

Pieters, C. M.↗
NASA NTRS1985

Spectroscopy of Moses Rock dike using remote sensing

Zeiss IR-photographs, NS0001 (TM simulator) and airborne imaging spectrometer (AIS) data were obtained for the Moses Rock kimberlite dike in southern Utah to identify and characterize the distinctive mafic mineralogy of the dike as well as the surrounding sedimentary rocks. The Zeiss and NS001 images provide information on the regional setting and allow units of the dike to be distinguished from the sediments. The AIS data are narrow images obtained in 128 near-infrared channels and provide characterizing information on the surface composition through. Three distinct spectroscopic units were found which have been tentatively identified as serpentized olivine-bearing soils found in the dike and two types of gypsum bearing soils found in the surrounding sedimentary soils.

Mustard, J. F.↗
NASA NTRS1986

Abundance and distribution of mineral components associated with Moses Rock (kimberlite) diatreme

The surface mineralogy in and around Moses Rock diatreme, a kimberlite-bearing dike in SW Utah, was examined using internally calibrated Airborne Imaging Spectrometer (AIS) data. Distinct near-infrared absorption characteristics of clays, gypsum, and serpentine (a key marker for kinberlite concentration) allowed the surface units containing these components to be identified spatially and the relative abundance of each component measured. Within the dike itself, channels and dispersed components of kimberlite and blocks of country rocks were accurately determined.

Mustard, J. F.↗
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 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 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 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 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 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 OSTI2021

Edge-Mediated Annihilation of Vacancy Clusters in Monolayer Molybdenum Diselenide (MoSe 2 ) under Electron Beam Irradiation

Here annihilation of vacancy clusters in monolayer molybdenum diselenide (MoSe2) under electron beam irradiation is reported. In situ high-resolution transmission electron microscopy observation reveals that the annihilation is achieved by diffusion of vacancies to the free edge near the vacancy clusters. Monte Carlo simulations confirm that it is energetically favorable for the vacancies to locate at the free edge. By computing the minimum energy path for the annihilation of one vacancy cluster as a case study, it is further shown that electron beam irradiation and pre-stress in the suspended MoSe2 monolayer are necessary for the vacancies to overcome the energy barriers for diffusion. The findings suggest a new mechanism of vacancy healing in 2D materials and broaden the capability of electron beam for defect engineering of 2D materials, a promising way of tuning their properties for engineering applications.

2D materials↗