Heterogeneous Defect Domains in Single‐Crystalline Hexagonal WS<sub>2</sub>

Jeong, Hyeong-Chai; Jin, Yinzhu; Yun, Seok Joon; Zhao, Jiong; Baik, Jaeyoon; Keum, Dong Hoon; Lee, Hyun Seok; Lee, Young Hee

doi:10.1002/adma.201605043

Cited by 152 publications

(158 citation statements)

References 26 publications

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“…This correlation of PL Stokes shift with absorption peak energy, but not with PL emission peak energy, strongly supports increased electron doping in the dark regions and, particularly, the narrower regions indicated in the insets of Figure 3, although we do not exclude the possible effects of minor compressive strain in the dark regions. 14,64 Away from these narrow regions connecting the centre to the apexes (i.e. in the yellow regions in the inset of Figure 3d), the slope of the correlation between Stokes shift and Aexciton absorption peak energy is reduced to β ∼ 0.52 and the strength of the correlation is also slightly reduced, with the Pearson's correlation coefficient down to 0.8.…”

Section: Resultsmentioning

confidence: 97%

Disentangling the effects of doping, strain and disorder in monolayer WS₂ by optical spectroscopy

Kolesnichenko¹,

Zhang²,

Zheng³

et al. 2020

2D Mater.

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Monolayers of transition metal dichalcogenides (TMdC) are promising candidates for realization of a new generation of optoelectronic devices. The optical properties of these two-dimensional materials, however, vary from flake to flake, or even across individual flakes, and change over time, all of which makes control of the optoelectronic properties challenging. There are many different perturbations that can alter the optical properties, including charge doping, defects, strain, oxidation, and water intercalation.Identifying which perturbations are present is usually not straightforward and requires 1 arXiv:1909.08214v1 [cond-mat.mtrl-sci] 18 Sep 2019 multiple measurements using multiple experimental modalities, which presents barriers when attempting to optimise preparation of these materials. Here, we apply highresolution photoluminescence and differential reflectance hyperspectral imaging in situ to CVD-grown WS 2 monolayers. By combining these two optical measurements and using a statistical correlation analysis we are able to disentangle three contributions modulating optoelectronic properties of these materials: electron doping, strain and defects. In separating these contributions, we also observe that the B-exciton energy is less sensitive to variations in doping density than A-excitons.

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Section: Resultsmentioning

confidence: 97%

Disentangling the effects of doping, strain and disorder in monolayer WS₂ by optical spectroscopy

Kolesnichenko¹,

Zhang²,

Zheng³

et al. 2020

2D Mater.

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“…A recently reported result suggests that the presence of either an S or W vacancy is more likely to lower the Raman frequency in a hexagonal WS 2 single crystal. 36 In this manner, the relatively softened E 2g 1 vibrations in both hexagonal mono-and bilayer MoS 2 likely result from an effect of vacancy induced defect states. We also studied the Raman spectral changes of triangular MoS 2 crystals with regards to various stacking orientations and thicknesses ranging from 1L to 6L.…”

Section: Synthesis Of Multi-stacked Mos 2 Crystalsmentioning

confidence: 99%

“…As illustrated by a recent study regarding a hexagonal WS 2 monolayer, defect states can be a key factor in reducing the PL emission in a localized fashion. 36 Moreover, the tailored PL intensity is also related to the band structure change via an extra-strain effect induced by merged defects. 37 The broadened and redshifted PL spectrum of the hexagonal monolayer compared to that of the triangular monolayer indicates the possible involvement of defect-assisted quenching in the PL emission.…”

Section: Synthesis Of Multi-stacked Mos 2 Crystalsmentioning

confidence: 99%

“…37 The broadened and redshifted PL spectrum of the hexagonal monolayer compared to that of the triangular monolayer indicates the possible involvement of defect-assisted quenching in the PL emission. 36 In fact, the activity of those defect states can be diminished using a nonoxidizing organic superacid, such as bis(trifluoromethane)sulfonimide, providing a drastic enhancement of the PL emission. 40,41 Thus, to reaffirm that the decreased PL intensity in our hexagonal crystal originates from defects, we dipped the samples in a bis(trifluoromethane)sulfonimide solution for 1 h and found that the PL emissions drastically recovered in both the triangles and hexagons.…”

Section: Synthesis Of Multi-stacked Mos 2 Crystalsmentioning

confidence: 99%

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Stacking-controllable interlayer coupling and symmetric configuration of multilayered MoS2

et al. 2018

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The stacking order in layered transition-metal dichalcogenides (TMDCs) induces variations in the electronic and interlayer couplings. Therefore, controlling the stacking orientations when synthesizing TMDCs is desirable but remains a significant challenge. Here, we developed and showed the growth kinetics of different shapes and stacking orders in as-grown multi-stacked MoS 2 crystals and revealed the stacking-order-induced interlayer separations, spin-orbit couplings (SOCs), and symmetry variations. Raman spectra in AA(A…)-stacked crystals demonstrated blueshifted out-of-plane (A 1g ) and in-plane (E 2g 1 ) phonon frequencies, representing a greater reduction of the van der Waals gap compared to conventional AB(A…)-stacking. Our observations, together with first-principles calculations, revealed distinct excitonic phenomena due to various stacking orientations. As a result, the photoluminescence emission was improved in the AA(A…)-stacking configuration. Additionally, calculations showed that the valence-band maxima (VBM) at the K point of the AA(A…)-stacking configuration was separated into multiple sub-bands, indicating the presence of stronger SOC. We demonstrated that AA(A…)-stacking emitted an intense second-harmonic signal (SHG) as a fingerprint of the more augmented non-centrosymmetric stacking and enabled SOC-induced splitting at the VBM. We further highlighted the superiority of four-wave mixing-correlated SHG microscopy to quickly resolve the symmetries and multi-domain crystalline phases of differently shaped crystals. Our study based on crystals with different shapes and multiple stacking configurations provides a new avenue for development of future optoelectronic devices.

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“…In optical properties, Carozo et al 66 reported lowtemperature defect-bound excitons in the edge regions of monolayer WS 2 due to the presence of a high concentration of monosulfur vacancies. Heterogeneous distributions of sulfur vacancies and tungsten vacancies have also been identified by Jeong et al, 67 thus forming triangular domains in hexagonal shaped WS 2 islands, which result in a segmented alternating photoluminescence (PL) intensity pattern. In bandgap engineering, a recent study on a quaternary alloy system, Mo x W 1-x Se 2(1-y) S 2y , has been reported by Susarla et al, 68 allowing a wider continuous tuning range (1.60~2.03 eV) than the ternary systems of Mo x W 1-x X 2 (X = S, Se) and MSe 2(1-x) S 2x (M = Mo, W).…”

Section: Structure-property Correlation Of Point Defects In 2d Matementioning

confidence: 75%

A machine perspective of atomic defects in scanning transmission electron microscopy

Dan

Zhao

Pennycook

2019

InfoMat

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Enabled by the advances in aberration‐corrected scanning transmission electron microscopy (STEM), atomic‐resolution real space imaging of materials has allowed a direct structure‐property investigation. Traditional ways of quantitative data analysis suffer from low yield and poor accuracy. New ideas in the field of computer vision and machine learning have provided more momentum to harness the wealth of big data and sophisticated information in STEM data analytics, which has transformed STEM from a localized characterization technique to a macroscopic tool with intelligence. In this review article, we discuss the prime significance of defect topology and density in two‐dimensional (2D) materials, which have proved to be a powerful means to tune a wide range of properties. Subsequently, we systematically review advanced data analysis methods that have demonstrated promising prospects in analyzing STEM data, particularly for identifying structural defects, with high throughput and veracity. A unified framework for atomic structure identification is also summarized.

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Heterogeneous Defect Domains in Single‐Crystalline Hexagonal WS₂

Cited by 152 publications

References 26 publications

Disentangling the effects of doping, strain and disorder in monolayer WS₂ by optical spectroscopy

Disentangling the effects of doping, strain and disorder in monolayer WS₂ by optical spectroscopy

Stacking-controllable interlayer coupling and symmetric configuration of multilayered MoS2

A machine perspective of atomic defects in scanning transmission electron microscopy

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Heterogeneous Defect Domains in Single‐Crystalline Hexagonal WS2

Cited by 152 publications

References 26 publications

Disentangling the effects of doping, strain and disorder in monolayer WS2 by optical spectroscopy

Disentangling the effects of doping, strain and disorder in monolayer WS2 by optical spectroscopy

Stacking-controllable interlayer coupling and symmetric configuration of multilayered MoS2

A machine perspective of atomic defects in scanning transmission electron microscopy

Contact Info

Product

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Heterogeneous Defect Domains in Single‐Crystalline Hexagonal WS₂

Disentangling the effects of doping, strain and disorder in monolayer WS₂ by optical spectroscopy

Disentangling the effects of doping, strain and disorder in monolayer WS₂ by optical spectroscopy