STEM Image Analysis Based on Deep Learning: Identification of Vacancy Defects and Polymorphs of MoS<sub>2</sub>

Lee, Kihyun; Park, Jinsub; Choi, Soyeon; Lee, Yangjin; Lee, Sol; Jung, Jinyoung; Lee, Jong‐Young; Ullah, Farman; Tahir, Zeeshan; Kim, Yong Soo; Lee, Gwan Hyoung; Kim, Kwanpyo

doi:10.1021/acs.nanolett.2c00550

Cited by 19 publications

(14 citation statements)

References 47 publications

(93 reference statements)

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“…To explore the possibility of the presence of multiple MoS 2 polymorphs , (i.e., 1T, 1H (2H-mono), 2H, and 3R), several dozens of NFs were thoroughly examined in each sample in terms of their lattice structure. In all monolayer NFs, only the thermodynamically favored 1H phase was identified, with no evidence of transversal displacement of one layer of sulfur atoms, characteristic of the 1T phase.…”

Section: Resultsmentioning

confidence: 99%

Green Colloidal Synthesis of MoS₂ Nanoflakes

Zechel,

Hutár,

Vretenár

et al. 2023

Inorg. Chem.

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Currently, two approaches dominate the large-scale production of MoS 2 : liquid-phase exfoliation, referred to as the top-down approach, and bottom-up colloidal synthesis from molecular precursors. Known colloidal synthesis approaches utilize toxic precursors. Here, an alternative green route for the bottom-up synthesis of MoS 2 nanoflakes (NFs) is described. The NFs were synthesized by colloidal synthesis using [Mo(CH 3 COO) 2 ] 2 and a series of sulfur (S)-precursors including thioacetamide (TAA), 3-mercaptopropionic acid (3-MPA), l -cysteine (L-CYS), mercaptosuccinic acid (MSA), 11-mercaptoundecanoic acid (MUA), 1-dodecanethiol (DDTH), and di- tert -butyl disulfide (DTBD). While TAA, an S-precursor most commonly used for MoS 2 NF preparation, is a known carcinogen, the other investigated S-precursors have low or no known toxicity. High-resolution scanning transmission electron microscopy (HR-STEM) and grazing incidence wide-angle X-ray scattering (GIWAXS) confirmed that in all cases, the syntheses yielded single-layer MoS 2 NFs with lateral sizes smaller than 15 nm and a well-defined crystal structure. Electronic absorption and Raman spectra showed characteristic features associated with the MoS 2 monolayers. The evolution of the absorption spectra of the growth solution during the syntheses reveals how the kinetics of the NF formation is affected by the S-precursor as well as the nature of the coordinating ligands.

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Section: Resultsmentioning

confidence: 99%

Green Colloidal Synthesis of MoS₂ Nanoflakes

Zechel,

Hutár,

Vretenár

et al. 2023

Inorg. Chem.

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“…The local atomic registries in our VHs were analyzed via atomic-resolution scanning transmission electron microscopy (STEM). Conventionally, high-angle annular dark field (HAADF) STEM is utilized to distinguish various stacking orders based on a Z -contrast mechanism Figure c,d shows HAADF-STEM images of R-type and H-type VHs near the edge of each top WS 2 layer, respectively.…”

Section: Resultsmentioning

confidence: 99%

“…Conventionally, high-angle annular dark field (HAADF) STEM is utilized to distinguish various stacking orders based on a Z-contrast mechanism. 28 Figure 2c,d shows HAADF-STEM images of R-type and H-type VHs near the edge of each top WS 2 layer, respectively. Again, there is no observable moirésuperlattice at the VH regions, at least within our experimental resolution, confirming the commensurate VHs.…”

Section: Resultsmentioning

confidence: 99%

Negative Valley Polarization of the Intralayer Exciton via One-Step Growth of H-Type Heterobilayer WS₂/MoS₂

Lee

Kim

et al. 2023

ACS Nano

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Vertical type II van der Waals heterobilayers of transition metal dichalcogenides (TMDs) have attracted wide attention due to their distinctive features mostly arising from the emergence of intriguing electronic structures that include moire-related phenomena. Owing to strong spin−orbit coupling under a noncentrosymmetric environment, TMD heterobilayers host nonequivalent +K and −K valleys of contrasting Berry curvatures, which can be optically controlled by the helicity of optical excitation. The corresponding valley selection rules are well established by not only intralayer excitons but also interlayer excitons. Quite intriguingly, here, we experimentally demonstrate that unusual valley switching can be achieved using the lowest-lying intralayer excitons in H-type heterobilayer WS 2 /MoS 2 prepared by one-step growth. This TMD combination provides an ideal case for interlayer coupling with an almost perfect lattice match, thereby also in the momentum space between +K and −K valleys in the H-type heterostructure. The underlying valley-switching mechanism can be understood by bright-to-dark conversion of initially created electrons in the valley of WS 2 , followed by interlayer charge transfer to the opposite valley in MoS 2 . Our suggested model is also confirmed by the absence of valley switching when the lowest-lying excitons in MoS 2 are directly generated in the heterobilayer. In contrast to the H-type case, we show that no valley switching is observed from R-type heterobilayers prepared by the same method, where interlayer charge transfer does not occur between the opposite valleys. We compare the case with the series of valley polarization data from other heterobilayer combinations obtained under different excitation energies and temperatures. Our valley switching mechanism can be utilized for valley manipulation by controlling the excitation photon energy together with the photon helicity in valleytronic devices derived from H-type TMD heterobilayers.

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“…Therefore, it can be difficult to identify the structural defects created by Ar‐plasma by STEM and TEM. [ 46 ] Alternatively, it has been demonstrated that Raman and PL signals are competent in characterizing plasma‐generated surface defects of ultrathin TMDs. [ 47–50 ] Figure 4b,c displays the Raman and PL spectra of MoS 2 under Ar‐plasma bombardment with different duration.…”

Section: Resultsmentioning

confidence: 99%

On‐Chip Investigation of Electrocatalytic Oxygen Reduction Reaction of 2D Materials

Wang

et al. 2022

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The on‐chip electrocatalytic microdevice (OCEM) is an emerging platform specialized in the electrochemical investigation of single‐entity nanomaterials, which is ideal for probing the intrinsic catalytic properties, optimizing performance, and exploring exotic mechanisms. However, the current catalytic applications of OCEMs are almost exclusively in electrocatalytic hydrogen/oxygen evolution reactions with minimized influence from the mass transfer. Here, an OCEM platform specially tailored to investigate the electrocatalytic oxygen reduction reaction (ORR) at a microscopic level by introducing electrolyte convection through a microfluidic flow cell is reported. The setup is established on gold microelectrodes and later successfully applied to investigate how Ar‐plasma treatment affects the ORR activities of 2H MoS2. This study finds that Ar‐plasma treatment significantly enhances the ORR performance of MoS2 nanosheets owing to the introduction of surface defects. This study paves the way for highly efficient microscopic investigation of diffusion‐controlled electrocatalytic reactions.

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STEM Image Analysis Based on Deep Learning: Identification of Vacancy Defects and Polymorphs of MoS₂

Cited by 19 publications

References 47 publications

Green Colloidal Synthesis of MoS₂ Nanoflakes

Green Colloidal Synthesis of MoS₂ Nanoflakes

Negative Valley Polarization of the Intralayer Exciton via One-Step Growth of H-Type Heterobilayer WS₂/MoS₂

On‐Chip Investigation of Electrocatalytic Oxygen Reduction Reaction of 2D Materials

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STEM Image Analysis Based on Deep Learning: Identification of Vacancy Defects and Polymorphs of MoS2

Cited by 19 publications

References 47 publications

Green Colloidal Synthesis of MoS2 Nanoflakes

Green Colloidal Synthesis of MoS2 Nanoflakes

Negative Valley Polarization of the Intralayer Exciton via One-Step Growth of H-Type Heterobilayer WS2/MoS2

On‐Chip Investigation of Electrocatalytic Oxygen Reduction Reaction of 2D Materials

Contact Info

Product

Resources

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STEM Image Analysis Based on Deep Learning: Identification of Vacancy Defects and Polymorphs of MoS₂

Green Colloidal Synthesis of MoS₂ Nanoflakes

Green Colloidal Synthesis of MoS₂ Nanoflakes

Negative Valley Polarization of the Intralayer Exciton via One-Step Growth of H-Type Heterobilayer WS₂/MoS₂