Relaxation and transfer of photoexcited electrons at a coplanar few-layer 1 T′/2H-MoTe2 heterojunction

Hu, Aiqin; Xu, Xiaolong; Liu, Wei; Xu, Shengnan; Xue, Zhiwei; Han, Bo; Wang, Shufeng; Gao, Peng; Sun, Quan; Gong, Qihuang; Ye, Yu; Lü, Guowei

doi:10.1038/s43246-020-00062-6

Cited by 13 publications

(18 citation statements)

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“…For instance, resonant exciton excitations (Figure b, c) remain localized with relatively homogeneous defects induced by the Si substrate serving as hole traps . The interface states at the flake edge create faster decaying defect pathways for electron cooling but slower multibody decay, which would seem to indicate that flakes formed in the shape with the smallest edge area would be best . However, Figure d shows hot exciton charge pooling along the interior of TMD flakes from lattice heterogeneities.…”

Section: Dynamic Pump−probe Measurement Techniquesmentioning

confidence: 99%

“…Defects are typically the result of chalcogen vacancies that can be filled through oxygen adsorption and create trap states. These trap states create nonradiative recombination pathways and are the primary mechanism of nonradiative energy loss in TMDs, though multibody Auger recombination also competes to diminish excited-state lifetimes. , TRPEEM measurements have the required temporal and spatial resolution necessary to successfully map nanometer size defect locations and their effects on excited carriers. This is especially needed considering the wide variety of flake shapes that monolayer TMDs can assume through tailored growth methods.…”

Section: Dynamic Pump−probe Measurement Techniquesmentioning

confidence: 99%

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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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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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“…Up to now, several state-of-the-art techniques, such as scanning ultrafast electron microscopy (SUEM), [22] scanning nearfield optical microscopy (SNOM), electron energy loss spectroscopy (EELS), and cathodoluminescence nanoscopy, have been demonstrated as powerful tools for studying electromagnetic waves on the nanoscale. In addition, photoemission electron microscopy (PEEM) [23][24][25][26][27][28][29] is a nonscanning high-spatial-resolution instrument that collects photoelectrons to image. The PEEM is a powerful tool for studying the surface wave modes of materials.…”

Section: Introductionmentioning

confidence: 99%

Ultraviolet/Visible Quasicylindrical Waves on Semimetal Cd₃As₂ Nanoplates

Xue

Zheng

et al. 2022

Advanced Photonics Research

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Resolving the photonic modes in real space is essential to understand the fundamental process and control of photonic behavior in optoelectric devices. However, the understanding of the photonic modes of semimetal Cd3As2 is still lacking. Herein, the quasicylindrical waves (QCW) on Cd3As2 nanoplates using photoemission electron microscopy (PEEM) are found out. The QCW is due to the optical field scattered by subwavelength indentations, with wavelength being the same as the incident light, and their amplitude decays as r−1/2 from the edges. The transverse magnetic (TM) mode dominates the observed QCW of Cd3As2 nanoplates, which is affected by the edge structure. In broadband from UV to visible, the QCWs on Cd3As2 nanoplates are observed. Further, nanostructures to achieve subwavelength focusing and interference lattice of the Cd3As2 optical QCW are achieved. These findings demonstrate the regulation of QCW, which benefits optimizing the optoelectronic performances of semimetal materials in the future.

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“…In this study, we aimed to clarify the dynamics of the excited electrons in the TADF process of a 4CzIPN solid‐state film, employing time‐resolved photoemission electron microscopy (TR‐PEEM) [ 29–36 ] (Figure 1a) and comparing it with TR‐PL. A significant advantage of the TR‐PEEM technique is the high sensitivity for the photoelectron signal.…”

Section: Introductionmentioning

confidence: 99%

“…The detection of such excited species is generally difficult even when using a transient absorption spectroscopic (TAS) technique, which is often employed to study optically dark excitonic species, including ionic ones. [28] In this study, we aimed to clarify the dynamics of the excited electrons in the TADF process of a 4CzIPN solid-state film, employing time-resolved photoemission electron microscopy (TR-PEEM) [29][30][31][32][33][34][35][36] (Figure 1a) and comparing it with TR-PL. A significant advantage of the TR-PEEM technique is the high sensitivity for the photoelectron signal.…”

Section: Introductionmentioning

confidence: 99%

Direct Observation of Photoexcited Electron Dynamics in Organic Solids Exhibiting Thermally Activated Delayed Fluorescence via Time‐Resolved Photoelectron Emission Microscopy

Fukami

Iwasawa

Sasaki

et al. 2021

Advanced Optical Materials

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Solid‐state films exhibiting thermally activated delayed fluorescence (TADF) can offer high internal electroluminescence (EL) quantum efficiency, even in a simplified device structure. However, the exciton dynamics in solid‐state TADF films, particularly for the unexpected exciton loss processes such as concentration quenching, have not yet been clarified. The dynamics of photoexcited electrons in the TADF process of a 2,4,5,6‐Tetra (9H‐carbazol‐9‐yl) isophthalonitrile (4CzIPN) solid film are observed via time‐resolved photoelectron emission microscopy (TR‐PEEM) and the results are compared with the conventional time‐resolved photoluminescence (TR‐PL) technique. The initial decay process of the photoexcited electrons probed via TR‐PEEM is thoroughly traced in the TR‐PL signal, while unusual long‐lived electrons are detected only through the use of TR‐PEEM. These results indicate that the excitons of 4CzIPN spontaneously dissociate into free carriers within the exciton lifetime, which seems to be a common process that contributes to the exciton loss in polar organic solids.

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Relaxation and transfer of photoexcited electrons at a coplanar few-layer 1 T′/2H-MoTe2 heterojunction

Cited by 13 publications

References 58 publications

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

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

Ultraviolet/Visible Quasicylindrical Waves on Semimetal Cd₃As₂ Nanoplates

Direct Observation of Photoexcited Electron Dynamics in Organic Solids Exhibiting Thermally Activated Delayed Fluorescence via Time‐Resolved Photoelectron Emission Microscopy

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Relaxation and transfer of photoexcited electrons at a coplanar few-layer 1 T′/2H-MoTe2 heterojunction

Cited by 13 publications

References 58 publications

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

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

Ultraviolet/Visible Quasicylindrical Waves on Semimetal Cd3As2 Nanoplates

Direct Observation of Photoexcited Electron Dynamics in Organic Solids Exhibiting Thermally Activated Delayed Fluorescence via Time‐Resolved Photoelectron Emission Microscopy

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Ultraviolet/Visible Quasicylindrical Waves on Semimetal Cd₃As₂ Nanoplates