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At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS2001

Optical Design of the MOSES Sounding Rocket Experiment

The Multi-Order Solar EUV Spectrograph (MOSES) is a sounding rocket payload now being developed by Montana State University in collaboration with the Goddard Space Flight Center, Lockheed Martin Advanced Technology Center, and Mullard Space Science Laboratory. The instrument utilizes a unique optical design to provide solar EUV measurements with true 2-pixel resolutions of 1.0 arcsec and 60 mA over a full two-dimensional field of view of 1056 x 528 arcsec, all at a time cadence of 10 s. This unprecedented capability is achieved by means of an objective spherical grating 100 mm in diameter, ruled at 833 gr/mm. The concave grating focuses spectrally dispersed solar radiation onto three separate detectors, simultaneously recording the zero-order as well as the plus and minus first-spectral-order images. Data analysis procedures, similar to those used in X-ray tomography reconstructions, can then disentangle the mixed spatial and spectral information recorded by the multiple detectors. A flat folding mirror permits an imaging focal length of 4.74 m to be packaged within the payload's physical length of 2.82 m. Both the objective grating and folding flat have specialized, closely matched, multilayer coatings that strongly enhance their EUV reflectance while also suppressing off-band radiation that would otherwise complicate data inversion. Although the spectral bandpass is rather narrow, several candidate wavelength intervals are available to carry out truly unique scientific studies of the outer solar atmosphere. Initial flights of MOSES, scheduled to begin in 2004, will observe a 10 Angstrom band that covers very strong emission lines characteristic of both the sun's corona (Si XI 303 Angstroms) and transition-region (He II 304 Angstroms). The MOSES program is supported by a grant from NASA's Office of Space Science.

Thomas, Roger J.↗
NASA NTRS2005

Narrow-band EUV Multilayer Coating for the MOSES Sounding Rocket

The Multi-order Solar EUV Spectrograph (MOSES) is a slitless spectrograph designed to study solar He II emission at 303.8 Angstroms, to be launched on a sounding rocket payload. One difference between MOSES and other slitless spectrographs is that the images are recorded simultaneously at three spectral orders, m = -1,0, +l. Another is the addition of a narrow-band multilayer coating on both the grating and the fold flat, which will reject out-of-band lines that normally contaminate the image of a slitless instrument. The primary metrics f a the mating were high peak reflectivity and suppression of Fe XV and XVI emission lines at 284 Angstroms and 335 Angstroms, respectively. We chose B4C/Mg2Si for our material combination since it provides better values for all three metrics together than the other leading candidates Si/Ir, Si/B4C or Si/SiC. Measurements of witness flats at NIST indicate the peak reflectivity at 303.6 is 38.5% for a 15 bilayer stack, while the suppression at 284 Angstroms, is 4.5x and at 335 Angstroms is 18.3x for each of two reflections in the instrument. We present the results of coating the MOSES flight gratings and fold flat, including the spectral response of the fold flat and grating as measured at NIST's SURF III and Brookhaven's X24C beamline.

Owens, Scott M.↗
DOE OSTI2023

Strain–Activated Stimulated Emission from Multilayer MoSe 2 in a Narrow Operation Window

Herein, photoluminescence (PL) and fluorescence lifetime imaging (FLIM) in multilayer MoSe 2 are studied. Strain-activated stimulated emission via defect levels in multilayer MoSe 2 under laser excitation is observed, for the first time in defects of transition metal dichalcogenides. The stimulated emission is indicated by a threshold behavior of PL emission intensity with respect to laser intensity, strong polarization effects, achieved population inversion with a difference in lifetimes of two competing excited states, and localization of the stimulated emission zone as observed in FLIM. Here, the presented results not only demonstrate strain-activated stimulated emission and highlight the necessity of strain engineering in tailoring 2D layered materials for optoelectronic applications, but also shed light on the design of stimulated emission in transition metal dichalcogenide's defects to tailor for potential single-photon emission behavior.

enhanced emission↗
DOE OSTI2025

Magnetism at the interface of MoSe 2 /V 2 O 5 heterostructures

In this study, we report the existence of magnetism in a heterostructure made up of an MoSe 2 transition metal dichalcogenide monolayer and a V 2 O 5 substrate. Using density functional theory simulations, we find that ferromagnetic ordering can be found in the MoSe 2 /V 2 O 5 heterostructure even though the individual components are nonmagnetic. The role of van der Waals interactions is examined.

2D magnet↗
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 OSTI2024

Twisted MoSe 2 Homobilayer Behaving as a Heterobilayer

Heterostructures (HSs) formed by the transition-metal dichalcogenides materials have shown great promise in next-generation (opto)electronic applications. An artificially twisted HS, allows us to manipulate the optical, and electronic properties. In this work, we introduce the understanding of the energy transfer (ET) process governed by the dipolar interaction in a twisted molybdenum diselenide (MoSe 2 ) homobilayer without any charge-blocking interlayer. We fabricated an unconventional homobilayer (i.e., HS) with a large twist angle by combining the 2 chemical vapor deposition (CVD) and mechanical exfoliation (Exf.) techniques to fully exploit the lattice parameters mismatch and indirect/direct (CVD/Exf.) bandgap nature. These effectively weaken the interlayer charge transfer and allow the ET to control the carrier recombination channels. Our experimental and theoretical results explain a massive HS photoluminescence enhancement due to an efficient ET process. This work shows that the electronically decoupled MoSe 2 homobilayer is coupled by the ET process, mimicking a 'true' heterobilayer nature.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Localized interlayer excitons in MoSe 2 –WSe 2 heterostructures without a moiré potential

Interlayer excitons (IXs) in MoSe 2 –WSe 2 heterobilayers have generated interest as highly tunable light emitters in transition metal dichalcogenide (TMD) heterostructures. Previous reports of spectrally narrow (<1 meV) photoluminescence (PL) emission lines at low temperature have been attributed to IXs localized by the moiré potential between the TMD layers. We show that spectrally narrow IX PL lines are present even when the moiré potential is suppressed by inserting a bilayer hexagonal boron nitride (hBN) spacer between the TMD layers. We compare the doping, electric field, magnetic field, and temperature dependence of IXs in a directly contacted MoSe 2 –WSe 2 region to those in a region separated by bilayer hBN. The doping, electric field, and temperature dependence of the narrow IX lines are similar for both regions, but their excitonic g-factors have opposite signs, indicating that the origin of narrow IX PL is not the moiré potential.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Percolative phase transition in few-layered MoSe 2 field-effect transistors using Co and Cr contacts

The metal-to-insulator phase transition (MIT) in two-dimensional (2D) materials under the influence of a gating electric field has revealed interesting electronic behavior and the need for a deeper fundamental understanding of electron transport processes, while attracting much interest in the development of next-generation electronic and optoelectronic devices. Although the mechanism of the MIT in 2D semiconductors is a topic under debate in condensed matter physics, our work demonstrates the tunable percolative phase transition in few-layered MoSe 2 field-effect transistors (FETs) using different metallic contact materials. Here, we attempted to understand the MIT through temperature-dependent electronic transport measurements by tuning the carrier density in a MoSe 2 channel under the influence of an applied gate voltage. In particular, we have examined this phenomenon using the conventional chromium (Cr) and ferromagnetic cobalt (Co) as two metal contacts. For both Cr and Co, our devices demonstrated n-type behavior with a room-temperature field-effect mobility of 16 cm 2 V −1 s −1 for the device with Cr-contacts and 92 cm 2 V −1 s −1 for the device with Co-contacts, respectively. Further, with low temperature measurements at 50 K, the mobilities increased significantly to 65 cm 2 V −1 s −1 for the device with Cr and 394 cm 2 V −1 s −1 for the device with Co-contacts. By fitting our experimental data to the percolative phase transition theory, the temperature-dependent conductivity data show a transition from an insulating-to-metallic behavior at a bias of ∼28 V for Cr-contacts and ∼20 V for Co-contacts. This cross-over of the conductivity can be attributed to an increase in carrier density as a function of the gate bias in temperature-dependent transfer characteristics. By extracting the critical exponents, we find that the transport behavior in the device with Co-contacts aligns closely with the 2D percolation theory. In contrast, the devices with Cr-contacts deviate significantly from the 2D limit at low temperatures.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Charge density wave activated excitons in TiSe 2 –MoSe 2 heterostructures

Layered materials enable the assembly of a new class of heterostructures where lattice-matching is no longer a requirement. Interfaces in these heterostructures therefore become a fertile ground for unexplored physics as dissimilar phenomena can be coupled via proximity effects. In this article, we identify an unexpected photoluminescence (PL) peak when MoSe 2 interacts with TiSe 2 . A series of temperature-dependent and spatially resolved PL measurements reveal that this peak is unique to the TiSe 2 –MoSe 2 interface, is higher in energy compared to the neutral exciton, and exhibits exciton-like characteristics. The feature disappears at the TiSe 2 charge density wave transition, suggesting that the density wave plays an important role in the formation of this new exciton. We present several plausible scenarios regarding the origin of this peak that individually capture some aspects of our observations but cannot fully explain this feature. These results therefore represent a fresh challenge for the theoretical community and provide a fascinating way to engineer excitons through interactions with charge density waves.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Effect of niobium doping on excitonic dynamics in MoSe 2

Abstract Transition metal dichalcogenides (TMDs) have emerged as attractive two-dimensional semiconductors for future electronic and optoelectronic applications. Their charge transport properties, such as conductivity and the type of charge carriers, can be effectively controlled by substitutional doping of the transition metal atoms. However, the effects of doping on the excitonic properties, particularly their dynamical properties, have been less studied. Using Nb-doped MoSe 2 as a case study, we experimentally investigate the effect of doping on excitonic dynamics in TMDs. Transient absorption measurements are used to directly compare the dynamical properties of excitons in Nb-doped MoSe 2 across monolayer, bilayer, and bulk flakes with their undoped counterparts. The exciton lifetimes in Nb-doped flakes are significantly shorter than those in their undoped counterparts. This effect is attributed to the trapping of excitons in defect states introduced by Nb impurities. These results reveal an important consequence of Nb doping on excitonic dynamics in TMDs.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2021

Coherent exciton-exciton interactions and exciton dynamics in a MoSe 2 / WSe 2 heterostructure

Coherent coupling between excitons is at the heart of many-body interactions and quantum information with transition metal dichalcogenide heterostructures as an emergent platform for the investigation of these interactions. We employ multidimensional coherent spectroscopy on monolayer MoSe 2 /WSe 2 heterostructures and observe coherent coupling between excitons spatially localized in monolayer MoSe 2 and WSe 2 . Through many-body spectroscopy, we further observe the absorption state arising from free interlayer electron-hole pairs. This observation yields a spectroscopic measurement of the interlayer exciton binding energy of about 250 meV.

36 MATERIALS SCIENCE↗
NASA NTRS1987

Abundance and distribution of ultramafic microbreccia in Moses Rock Dike: Quantitative application of AIS data

Moses Rock dike is a Tertiary diatreme containing serpentinized ultramafic microbreccia (SUM). Field evidence indicates the SUM was emplaced first followed by breccias derived from the Permian strata exposed in the walls of the diatreme and finally by complex breccias containing basement and mantle derived rocks. SUM is found primarily dispersed throughout the matrix of the diatreme. Moses Rock dike was examined with Airborne Imaging Spectrometer (AIS) to map the distribution and excess of SUM in the matrix and to better understand the nature of the eruption which formed this explosive volcanic feature. AIS data was calibrated by dividing the suite of AIS data by data from an internal standard area and then multiplying this relative reflectance data by the absolute bidirectional reflectance of a selected sample from the standard area which was measured in the lab. From the calibrated AIS data the minerals serpentine, gypsum, and illite as well as desert varnish and the lithologies SUM and other sandstones were identified. SUM distribution and abundance in the matrix of the diatreme were examined in detail and two distinct styles of SUM dispersion were observed. The two styles are discussed in detail.

Mustard, John F.↗
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 (2.67 Å) and four longer (2.73 Å) Mo–Mo bond lengths. There are a spread of Mo–Se bond distances ranging from 2.64–2.72 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 (2.67 Å) and two longer (2.73 Å) Mo–Mo bond lengths. There are a spread of Mo–Se bond distances ranging from 2.64–2.72 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 2.64–2.72 Å. In is bonded in a trigonal planar geometry to three Se atoms. All In–Se bond lengths are 3.31 Å. There are three 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. In the third 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 Li(MoSe)3 by Materials Project

Li(MoSe)3 crystallizes in the hexagonal P6_3/m 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 2.58 Å. Mo is bonded in a distorted see-saw-like geometry to six equivalent Mo and four equivalent Se atoms. There are two shorter (2.67 Å) and four longer (2.74 Å) Mo–Mo bond lengths. There are a spread of Mo–Se bond distances ranging from 2.63–2.72 Å. Se is bonded in a 1-coordinate geometry to one Li and four equivalent Mo atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Tl(MoSe)3 by Materials Project

Tl(MoSe)3 crystallizes in the hexagonal P6_3/m space group. The structure is three-dimensional. Mo is bonded in a distorted see-saw-like geometry to six equivalent Mo and four equivalent Se atoms. There are two shorter (2.67 Å) and four longer (2.73 Å) Mo–Mo bond lengths. There are a spread of Mo–Se bond distances ranging from 2.63–2.71 Å. Tl is bonded in a trigonal planar geometry to three equivalent Se atoms. All Tl–Se bond lengths are 3.15 Å. Se is bonded in a 5-coordinate geometry to four equivalent Mo and one Tl atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Na(MoSe)3 by Materials Project

Na(MoSe)3 crystallizes in the monoclinic P2_1/m space group. The structure is three-dimensional. Na is bonded in a 12-coordinate geometry to three Mo and nine Se atoms. All Na–Mo bond lengths are 3.66 Å. There are a spread of Na–Se bond distances ranging from 3.28–3.50 Å. There are three inequivalent Mo sites. In the first Mo site, Mo is bonded in a distorted see-saw-like geometry to one Na and four Se atoms. There are two shorter (2.64 Å) and two longer (2.72 Å) Mo–Se bond lengths. In the second Mo site, Mo is bonded in a distorted see-saw-like geometry to one Na and four Se atoms. There are two shorter (2.64 Å) and two longer (2.72 Å) Mo–Se bond lengths. In the third Mo site, Mo is bonded in a distorted see-saw-like geometry to one Na and four Se atoms. There are two shorter (2.64 Å) and two longer (2.72 Å) Mo–Se bond lengths. There are three inequivalent Se sites. In the first Se site, Se is bonded in a 7-coordinate geometry to three equivalent Na and four Mo atoms. In the second Se site, Se is bonded in a 7-coordinate geometry to three equivalent Na and four Mo atoms. In the third Se site, Se is bonded in a 7-coordinate geometry to three equivalent Na and four Mo atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on KIn(MoSe)6 by Materials Project

KIn(MoSe)6 crystallizes in the monoclinic Pm space group. The structure is three-dimensional. K is bonded in a trigonal planar geometry to three Se atoms. There are one shorter (3.21 Å) and two longer (3.22 Å) K–Se bond lengths. There are six 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 2.61–2.72 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 (2.66 Å) and four longer (2.74 Å) Mo–Mo bond lengths. There are a spread of Mo–Se bond distances ranging from 2.62–2.72 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 two shorter (2.73 Å) and two longer (2.74 Å) Mo–Mo bond lengths. There are a spread of Mo–Se bond distances ranging from 2.63–2.72 Å. In the fourth Mo site, Mo is bonded in a distorted see-saw-like geometry to six Mo and four Se atoms. There are one shorter (2.67 Å) and one longer (2.68 Å) Mo–Mo bond lengths. There are a spread of Mo–Se bond distances ranging from 2.64–2.72 Å. In the fifth Mo site, Mo is bonded in a distorted see-saw-like geometry to six Mo and four Se atoms. The Mo–Mo bond length is 2.66 Å. There are a spread of Mo–Se bond distances ranging from 2.65–2.72 Å. In the sixth 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 2.63–2.72 Å. In is bonded in a trigonal planar geometry to three Se atoms. There are one shorter (3.16 Å) and two longer (3.17 Å) In–Se bond lengths. There are six inequivalent Se sites. In the first Se site, Se is bonded in a 5-coordinate geometry to one K and four Mo atoms. In the second Se site, Se is bonded in a 5-coordinate geometry to one K and four Mo atoms. In the third Se site, Se is bonded in a 5-coordinate geometry to one K and four Mo atoms. In the fourth Se site, Se is bonded in a 5-coordinate geometry to four Mo and one In atom. In the fifth Se site, Se is bonded in a 5-coordinate geometry to four Mo and one In atom. In the sixth 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 Rb(MoSe)3 by Materials Project

Rb(MoSe)3 crystallizes in the hexagonal P6_3/m space group. The structure is three-dimensional. Rb is bonded in a 9-coordinate geometry to nine equivalent Se atoms. There are three shorter (3.61 Å) and six longer (3.65 Å) Rb–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 Rb and four equivalent Mo atoms.

36 MATERIALS SCIENCE↗