Defect-related dynamics of photoexcited carriers in 2D transition metal dichalcogenides

Gao, Lei; Hu, Zhenliang; Jun, Lu; Liu, Hongwei; Ni, Zhenhua

doi:10.1039/d1cp00006c

Cited by 17 publications

(16 citation statements)

References 133 publications

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“…Reports have shown that defects impact the exciton dynamics of neutral excitons by providing additional relaxation channels . Another study reported that defect-bound excitons exhibit a much longer valley lifetime, and the prolonged PL lifetime is also attributed to defects for reducing exciton–exciton annihilation (EEA) in monolayer WS 2 . The lifetime measurement in our study showed similar dynamics.…”

Section: Resultssupporting

confidence: 79%

“…67 Another study reported that defect-bound excitons exhibit a much longer valley lifetime, 66 and the prolonged PL lifetime 10 is also attributed to defects for reducing exciton− exciton annihilation (EEA) in monolayer WS 2 . 45 The lifetime 68 measurement in our study showed similar dynamics. The defective conditions displayed a longer decay time relative to the pristine condition, as shown in Figure 5c.…”

Section: ■ Results and Discussionsupporting

confidence: 77%

“…Atomic resolution imaging using STEM plays an essential role in identifying the defect type and quantifying the vacancy concentration. , The STEM study was designed based on the Figure a conditions to reveal the physical properties as the function of vacancy concentrations, where Figure a–c corresponds to samples with low, medium, and high vacancy concentrations, respectively. Figure consists of three separate high-angle annular dark-field (HAADF) STEM images where the hexagonal lattice of the MoSe 2 structure can be seen.…”

Section: Resultsmentioning

confidence: 99%

“…The top-down approach typically starts with using the already synthesized pristine crystals followed by postprocessing steps to generate the defects and vacancies. Different types of defects such as chalcogen atom vacancies (single or double), metal vacancies, antisites, and line defects have been manufactured in these methods. However, control over the formation, distribution, and types of defects while keeping the integrity of the crystal is still a challenge in such top-down postprocessing techniques .…”

Section: Introductionmentioning

confidence: 99%

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Laser-Assisted Synthesis of Monolayer 2D MoSe₂ Crystals with Tunable Vacancy Concentrations: Implications for Gas and Biosensing

Azam

Boebinger

Jaiswal

et al. 2022

ACS Appl. Nano Mater.

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Tuning the structural and electronic properties of atomically thin two-dimensional (2D) materials via defect and vacancy engineering is the key to enabling their potential use in various applications, including electronics, energy, and sensing devices. Vacancies are, for instance, becoming highly promising for the enhanced interaction of gases and biomolecules with 2D materials in energy and sensing applications. However, the deterministic generation of desirable vacancies with tunable concentrations remains a challenge in 2D materials due to the limitations in the current growth methods, such as the complex reaction chemistries and gas flow dynamics. Therefore, engineering defects and vacancies in 2D materials have been mainly limited to destructive top-down processes such as heating, ion bombardments, and laser postprocessing. Here, we introduce a single-step bottom-up synthesis approach for the growth of monolayer MoSe2 crystals with tunable vacancy concentrations. This method utilizes the spatiotemporal properties and adjustable power densities of the lasers to control the vaporization dynamics of the stoichiometric MoSe2 powders. Such a mechanism in the vaporization allows us to grow tunable stoichiometry monolayer MoSe2–x crystals on the substrates. The localized and time-controlled (250 ms to 2 s) vaporization of the MoSe2 powder by a CO2 laser enables the formation of monolayer crystals with controlled vacancy concentrations ranging from ∼1 to 20%. The effects of laser power, laser irradiation time, and background pressure on the tuning range and subsequent properties of the crystals are investigated and quantified using Raman and photoluminescence spectroscopy, scanning transmission electron microscopy (STEM), and time-correlated single-photon counting (TCSPC). This bottom-up synthesis is a promising approach that allows the deterministic vacancy tuning for future electronics and, in particular, gas and biosensing applications without the need for further postprocessing and potential structural disruption of the crystals.

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Section: Resultssupporting

confidence: 79%

Section: ■ Results and Discussionsupporting

confidence: 77%

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Laser-Assisted Synthesis of Monolayer 2D MoSe₂ Crystals with Tunable Vacancy Concentrations: Implications for Gas and Biosensing

Azam

Boebinger

Jaiswal

et al. 2022

ACS Appl. Nano Mater.

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“…In addition, the increasing trend of τ 2 with pump fluence in Figure 3e agrees with the behavior of defect carrier trapping, which is typically observed in 2D materials with diverse time scales of sub‐ps to 100‐ps. [ 79,80 ] Thus, we tentatively attribute the τ 2 dynamics to the trapping of carriers in the valleys at non‐Γ points (an extended discussion is presented in Figure S11, Supporting Information). However, more theoretical and experimental studies are required to confirm this because neither the defect levels nor the temperature dependence of τ 2 is yet to be determined.…”

Section: Resultsmentioning

confidence: 88%

Completely Anisotropic Ultrafast Optical Switching and Direction‐Dependent Photocarrier Diffusion in Layered ZrTe₅

Seo

Nah

Sajjad

et al. 2022

Advanced Optical Materials

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In particular, their optical anisotropy has enabled novel light-polarization-driven applications, such as highly polarizationsensitive light detectors and emitters [3,[10][11][12][13][14][15][16][17] and optical information encryption. [18] Recently, the ultrafast control of the anisotropic optical properties of 2D materials has become a topic of interest, since it not only enables high-speed, polarizationcontrolled optical switches but also offers novel physical insights into anisotropic light-matter interactions and quantum coherences. [19][20][21][22][23][24][25][26][27][28][29] Moreover, their ultrafast spatiotemporal dynamics exhibit unique quasi-1D behavior of photocarriers with direction-dependent mobilities and diffusivities, offering essential information for improving the anisotropic devices. [30,31] However, despite the continuous emergence of novel anisotropic 2D materials, [6][7][8][9] ultrafast optical anisotropy has so far been explored for only a very limited class of materials.ZrTe 5 is a transition metal pentatelluride that has been extensively studied since the 1980s owing to its unique physical properties, such as resistivity anomaly (Figure S1, Supporting information), [32,33] large thermoelectric power, [34,35] and pressure-induced superconductivity. [36] In particular, ZrTe 5 exhibits different topological phases (weak and strong topological insulators and Dirac semimetal) in diverse experiments, its topological nature has been a topic of active debate in the last decade. [37][38][39][40][41][42][43] Further, recent studies demonstrated that transitions between these topological Layered nanomaterials with in-plane anisotropy exhibit unique orientationdependent responses to external stimuli, enabling the development of novel devices with additional degrees of freedom. In particular, their anisotropic optical properties enable ultrafast nanophotonic modulators to be controlled by light polarization. However, achieving high controllability is still challenging due to incomplete optical anisotropy in most materials. Here, this work presents a completely anisotropic, ultrafast optical modulation in zirconium pentatelluride (ZrTe 5 ), a layered nanomaterial that has recently attracted renewed attention. The transient absorption (TA) microscopy reveals anisotropic ultrafast picosecond optical modulation in a broad range of 1.2-2.2 eV. In particular, at a certain photon-energy of 1.62 eV, complete on/off switching with a near-unity degree of anisotropy is achieved solely by changing the light polarization, suggesting that ZrTe 5 is a promising material for polarization-selective high-speed optical modulators. The theoretical analysis of the transition dipole moments attributes this sharp anisotropy to strongly polarization-dependent excited-state absorption. Furthermore, this work directly observes direction-dependent photocarrier transport using scanning TA microscopy. It yields the anisotropic diffusivity, mobility, and diffusion lengths of the photocarriers, which are essential parameters for de...

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Fractal Growth of 2D NbSe₂ for Broadband Nonlinear Optical Limiting

Wang,

Ma,

Wang

et al. 2024

Adv Funct Materials

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The compelling demand for laser protection both for civil and defense use calls for new‐generation nonlinear optical materials. Chemical vapor deposition (CVD) techniques provide extra tricks to modulate crystal optical nonlinearity through fractal growth. The synthesized 2D NbSe2 and its fractal structures exhibit giant, broadband laser attenuation behaviors extending into the near Infrared (NIR) range. Particularly, the optical limiting performance generally correlates with the fractal dimension, where Fractal NbSe2 demonstrates enhanced third‐order optical nonlinearity at a huge nonlinear absorption coefficient of 9.7 × 10−4 m W−1 and an ultralow starting threshold of 5 mJ cm−2 at 532 nm. Various techniques include femtosecond spectroscopy, Density functional theory (DFT) calculation and Kelvin probe force microscopy disclose the origin of the strong nonlinearity of the 2D NbSe2 crystals, and suggest the formation of edge states and overall faster carrier dynamics, larger surface contact potential difference NbSe2 fractals contribute to their even augmented nonlinear responses. Fractal engineering thus opens new avenues to fabricate highly efficient laser protection materials, and the blocking of intense beam (a large attenuation factor over 13.3 dB at 532 nm) while allowing transmission of weak one (a high linear optical transmittance over 80%) fulfills the much desired “smart” defense.

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Defect-related dynamics of photoexcited carriers in 2D transition metal dichalcogenides

Abstract: Two-dimensional (2D) transition metal dichalcogenides (TMDs) exhibit enormous potential in the field of optoelectronics because of their attractive optoelectronic properties, such as strong excitonic emissions, spin splited band structure, palpable...

Cited by 17 publications

References 133 publications

Laser-Assisted Synthesis of Monolayer 2D MoSe₂ Crystals with Tunable Vacancy Concentrations: Implications for Gas and Biosensing

Laser-Assisted Synthesis of Monolayer 2D MoSe₂ Crystals with Tunable Vacancy Concentrations: Implications for Gas and Biosensing

Completely Anisotropic Ultrafast Optical Switching and Direction‐Dependent Photocarrier Diffusion in Layered ZrTe₅

Fractal Growth of 2D NbSe₂ for Broadband Nonlinear Optical Limiting

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Defect-related dynamics of photoexcited carriers in 2D transition metal dichalcogenides

Abstract: Two-dimensional (2D) transition metal dichalcogenides (TMDs) exhibit enormous potential in the field of optoelectronics because of their attractive optoelectronic properties, such as strong excitonic emissions, spin splited band structure, palpable...

Cited by 17 publications

References 133 publications

Laser-Assisted Synthesis of Monolayer 2D MoSe2 Crystals with Tunable Vacancy Concentrations: Implications for Gas and Biosensing

Laser-Assisted Synthesis of Monolayer 2D MoSe2 Crystals with Tunable Vacancy Concentrations: Implications for Gas and Biosensing

Completely Anisotropic Ultrafast Optical Switching and Direction‐Dependent Photocarrier Diffusion in Layered ZrTe5

Fractal Growth of 2D NbSe2 for Broadband Nonlinear Optical Limiting

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Product

Resources

About

Laser-Assisted Synthesis of Monolayer 2D MoSe₂ Crystals with Tunable Vacancy Concentrations: Implications for Gas and Biosensing

Laser-Assisted Synthesis of Monolayer 2D MoSe₂ Crystals with Tunable Vacancy Concentrations: Implications for Gas and Biosensing

Completely Anisotropic Ultrafast Optical Switching and Direction‐Dependent Photocarrier Diffusion in Layered ZrTe₅

Fractal Growth of 2D NbSe₂ for Broadband Nonlinear Optical Limiting