Cross-Examination of Ultrafast Structural, Interfacial, and Carrier Dynamics of Supported Monolayer MoS<sub>2</sub>

He, Xing; Chebl, Mazhar; Yang, Ding‐Shyue

doi:10.1021/acs.nanolett.9b05344

Cited by 21 publications

(29 citation statements)

References 52 publications

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“…The reported risetime for the MSD following photoexcitation (i.e. the observed Debye-Waller decay of Bragg peak intensities) in the case of 1L-MoS 2 on sapphire is slower than reported here, 37,38 while the opposite is true for 1L-MoS 2 on SiO 2 . 39 This is as expected based on the dielectric constants of these substrate materials, providing additional evidence in support of our conclusions regarding dielectric screening of the electron-phonon interaction in 1L-MoS 2 .…”

Section: Dielectric Screening Of Epc In the 1l-mos 2 /Si:n Heterostru...contrasting

confidence: 65%

“…[29][30][31][32][33] To date, experimental investigations of EPC effects and nonequilibrium phonon dynamics in monolayer and few-layer TMDs have been limited to what can be learned about zone-centered optical phonons via conventional and time-resolved Raman spectroscopy [34][35][36] or averaged atomic meansquared displacements via UED. [37][38][39] The momentum selectivity of phonon emission and the time-dependent anisotropic phonon populations, expected throughout the Brillouin zone (BZ) of TMDs, 21,26 is hidden from view with these techniques. By contrast, UEDS provides momentum-resolved information on EPC and its modification due to (i) the dielectric environment, (ii) nonequilibrium phonon relaxation in 1L-MoS 2 (including anharmonic decay within the monolayer), and (iii) phonon transport to the underlying substrate as we show here.…”

Section: Introductionmentioning

confidence: 99%

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Direct view of phonon dynamics in atomically thin MoS$_{2}$

Britt,

Li,

de Cotret

et al. 2022

Preprint

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Transition metal dichalcogenide monolayers and heterostructures are highly tunable material systems that provide excellent models for physical phenomena at the two-dimensional (2D) limit. While most studies to date have focused on electrons and electron-hole pairs, phonons also play essential roles. Here, we apply ultrafast electron diffraction and diffuse scattering to directly quantify, with time and momentum resolution, electron-phonon coupling (EPC) in monolayer molybdenum disulfide (MoS 2 ) and phonon transport from the monolayer to a silicon nitride (Si 3 N 4 ) substrate. Optically generated hot carriers result in a profoundly anisotropic distribution of phonons in the monolayer on the ∼ 5 ps time scale. A quantitative comparison with ab-initio ultrafast dynamics simulations reveals the essential role of dielectric screening in weakening EPC. Thermal transport from the monolayer to the substrate occurs with the phonon system far from equilibrium. While screening in 2D is known to strongly affect equilibrium properties, our findings extend this understanding to the dynamic regime.

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Section: Dielectric Screening Of Epc In the 1l-mos 2 /Si:n Heterostru...contrasting

confidence: 65%

Section: Introductionmentioning

confidence: 99%

Direct view of phonon dynamics in atomically thin MoS$_{2}$

Britt,

Li,

de Cotret

et al. 2022

Preprint

View full text Add to dashboard Cite

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“…We also note the lack of notable intensity changes near the shadow edge (Figure 2a), which rules out the possibility of significant transient surface electric fields as the explanation for the observed diffraction changes (see the Supporting Information). 23 Because the elastic mean free path of 30 keV electrons in methanol is about 108 nm, only the layers within the top few nm are probed at the grazing incidence of ∼1°. Thus, timedependent experiments conducted with different film thicknesses allow the examination of the structural dynamics of 2D methanol assemblies at different distances above the solid− molecule interface.…”

mentioning

confidence: 99%

Order-Determined Structural and Energy Transport Dynamics in Solid-Supported Interfacial Methanol

Yang

2021

Nano Lett.

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Energy transport dynamics in different nanostructures are crucial to both a fundamental understanding of and practical applications for heat management at the nanoscale. It has been reported that thermal conductivity may be severely impacted by stacking disorder in layered materials. Here, using ultrafast electron diffraction in the reflection geometry for direct probing of structural dynamics, we report a fundamental behavioral difference due to stacking order in an entirely different systemsolidsupported methanol assemblies whose layered structures may resemble those of two-dimensional (2D) and van der Waals (vdW) solids but with much weaker in-plane hydrogen bonds. Thermal diffusion is found to be the transport mechanism across 2D-layered films without a crossplane stacking order. In stark contrast, much faster ballistic energy transport is observed in 3D-ordered crystalline solids. The major change in such dynamical behavior may be associated with the efficiency of vibrational coupling between vdW-interacted methanol layers, which demonstrates a strong structure−property relation.

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Section: Dynamic Pump−probe Measurement Techniquesmentioning

confidence: 99%

Section: Dynamic Pump−probe Measurement Techniquesmentioning

confidence: 99%

Imaging Excited-State Dynamics in Two-Dimensional Semiconductors with Emerging Ultrafast Measurement Techniques

2021

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Metrics & MoreArticle Recommendations CONSPECTUS: Two-dimensional halide perovskites (HPs) and monolayer transition metal dichalcogenides (TMDs) are two families of direct band gap semiconductors of particular interest for their unique structural and optoelectronic properties. These materials confine the motion of charge carriers to a single plane which increases the exciton binding energy, increases the stability of multibody particles, and decreases mobility. Despite great progress in recent years, the widespread understanding of fundamental properties of these materials is limited by a number of remaining issues including (i) the effects of Rashba splitting and intravalley dynamics on recombination lifetimes; (ii) the effects of passivation of photoinduced and substrate-induced defects on trap state recombination (iii) the contribution of lattice variations and phase transitions on material properties. These properties influence the material and electronic dynamics on time scales in the range of femtoseconds to nanoseconds, and as such, they require equally fast measurements in order to be investigated. In this perspective, three particular ultrafast pump−probe measurement techniques are highlighted for their ability to provide crucial insights into these unresolved issues. Time-resolved circular dichroism spectroscopy (TRCDS) uses circularly polarized beams to selectively populate and interrogate carriers in spin split valleys, investigate Rashba splitting, and explore valley dynamics. There have been mixed results showing Rashba splitting using TRCDS to study pure 2D HPs, though it has successfully shown the splitting in quasi-2D perovskites with an even number of layers and HPs using chiral organic cations. In monolayer TMDs, it has been used extensively to study spin selective valley dynamics, trion and biexciton dynamics, and now the focus turns to investigating Janus TMDs. Time-resolved photoemission microscopy uses an ionizing probe beam to eject electrons which are then measured to map defects caused by photoexcitation, substrate interactions, and halide migration. At present there have been no results published on 2D HPs, though it has been used in 3D HPs to investigate defect-induced traps. In monolayer TMDs, defects have a large effect on charge carrier properties, and results have shown nanometer sized defects and charge pooling. Finally, time-resolved ultrafast electron measurements use an electron beam probe to measure lattice deformations and substrate interface dynamics. In 2D HPs, this technique shows the octahedral tilting that occurs as a result of hot carrier-lattice thermalizations and exciton-polarons. In monolayer TMDs, the wrinkling deformations that occur as a result of phonon modes can be imaged and the effect of the substrate on the atomic motions can be examined. This perspective concludes with an outline of the challenges corresponding to these measurements. We discuss the damaging effects and defects induced by using high energy electron pulses and the methods for mitigating these...

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Cross-Examination of Ultrafast Structural, Interfacial, and Carrier Dynamics of Supported Monolayer MoS₂

Cited by 21 publications

References 52 publications

Direct view of phonon dynamics in atomically thin MoS$_{2}$

Direct view of phonon dynamics in atomically thin MoS$_{2}$

Order-Determined Structural and Energy Transport Dynamics in Solid-Supported Interfacial Methanol

Imaging Excited-State Dynamics in Two-Dimensional Semiconductors with Emerging Ultrafast Measurement Techniques

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Cross-Examination of Ultrafast Structural, Interfacial, and Carrier Dynamics of Supported Monolayer MoS2

Cited by 21 publications

References 52 publications

Direct view of phonon dynamics in atomically thin MoS$_{2}$

Direct view of phonon dynamics in atomically thin MoS$_{2}$

Order-Determined Structural and Energy Transport Dynamics in Solid-Supported Interfacial Methanol

Imaging Excited-State Dynamics in Two-Dimensional Semiconductors with Emerging Ultrafast Measurement Techniques

Contact Info

Product

Resources

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Cross-Examination of Ultrafast Structural, Interfacial, and Carrier Dynamics of Supported Monolayer MoS₂