Stacking-dependent optical properties in bilayer WSe<sub>2</sub>

McCreary, Kathleen M.; Phillips, Madeleine; Chuang, Hsun-Jen; Wickramaratne, Darshana; Rosenberger, Matthew R.; Hellberg, C. Stephen; Jonker, B. T.

doi:10.1039/d1nr06119d

Cited by 26 publications

(26 citation statements)

References 46 publications

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“…However, when the incident laser resonantly excited the A exciton (1.63 and 1.65 eV data), contrast between the domains clearly emerges. [ 46 ] In accordance to previous theoretical calculations, [ 53 ] the breaking of inversion symmetry in the 3R‐bilayer leads to additional splitting of the valance band maximum around K points, which further results in split exciton resonances. Thus, correlating these complementary nonlinear optical imaging modalities allows us to unambiguously establish the crystal‐symmetry‐based origins of the contrast in local optical response.…”

Section: Resultssupporting

confidence: 86%

“…The flake of interest includes both monolayer and bilayer regions. The dark‐colored bilayer region has a jigsaw‐like pattern, which is formed by multiple triangular domains with 3R and 2H stacking order, [ 46 ] as confirmed below using both nonlinear nano‐SHG and linear scattering scanning nearfield optical microscopy (s‐SNOM). AFM topography of the boxed area is shown in Figure 3b, where the bilayer and monolayer regions can be clearly distinguished by height.…”

Section: Resultsmentioning

confidence: 89%

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Nanoscale Optical Imaging of 2D Semiconductor Stacking Orders by Exciton‐Enhanced Second Harmonic Generation

Yao

Zhang

Yanev

et al. 2022

Advanced Optical Materials

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Second harmonic generation (SHG) is a nonlinear optical response arising exclusively from broken inversion symmetry in the electric‐dipole limit. Recently, SHG has attracted widespread interest as a versatile and noninvasive tool for characterization of crystal symmetry and emerging ferroic or topological orders in quantum materials. However, conventional far‐field optics is unable to probe local symmetry at the deep subwavelength scale. Here, near‐field SHG imaging of 2D semiconductors and heterostructures with the spatial resolution down to 20 nm is demonstrated using a scattering‐type nano‐optical apparatus. It is shown that near‐field SHG efficiency is greatly enhanced by excitons in atomically thin transition metal dichalcogenides. Furthermore, by correlating nonlinear and linear scattering‐type nano‐imaging, nanoscale variations of interlayer stacking order in bilayer WSe2 are resolved, and the stacking‐tuned excitonic light–matter interactions are revealed. This work demonstrates nonlinear optical interrogation of crystal symmetry and structure–property relationships at the nanometer length scales relevant to emerging properties in quantum materials.

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Section: Resultssupporting

confidence: 86%

Section: Resultsmentioning

confidence: 89%

Nanoscale Optical Imaging of 2D Semiconductor Stacking Orders by Exciton‐Enhanced Second Harmonic Generation

Yao

Zhang

Yanev

et al. 2022

Advanced Optical Materials

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“…Raman spectroscopy is a nondestructive optical technique often used to provide a fingerprint of 2D materials systems, identifying the number of layers as well as providing insights into defect densities and interlayer interactions. , Recently, Raman spectroscopy has been used to identify phonon modes associated with moiré superlattices in twisted bilayers of MoS 2 and WS 2 and stacking-dependent behavior in homobilayers of WSe 2 , demonstrating that it is a powerful tool for probing systems that are sensitive to interlayer twist. In particular, Quan et al have also shown that small changes in twist angle in bilayer MoS 2 can lead to pronounced shifts in the frequencies of acoustic phonons, while the Raman-active optical phonon frequencies are only weakly dependent on twist angle .…”

Section: Introductionmentioning

confidence: 99%

Emergent Moiré Phonons Due to Zone Folding in WSe₂–WS₂ Van der Waals Heterostructures

et al. 2022

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Bilayers of 2D materials offer opportunities for creating devices with tunable electronic, optical, and mechanical properties. In van der Waals heterostructures (vdWHs) where the constituent monolayers have different lattice constants, a moiré superlattice forms with a length scale larger than the lattice constant of either constituent material regardless of twist angle. Here, we report the appearance of moiré Raman modes from nearly aligned WSe2–WS2 vdWHs in the range of 240–260 cm–1, which are absent in both monolayers and homobilayers of WSe2 and WS2 and in largely misaligned WSe2–WS2 vdWHs. Using first-principles calculations and geometric arguments, we show that these moiré Raman modes are a consequence of the large moiré length scale, which results in zone-folded phonon modes that are Raman active. These modes are sensitive to changes in twist angle, but notably, they occur at identical frequencies for a given small twist angle away from either the 0-degree or 60-degree aligned heterostructure. Our measurements also show a strong Raman intensity modulation in the frequency range of interest, with near 0 and near 60-degree vdWHs exhibiting a markedly different dependence on excitation energy. In near 0-degree aligned WSe2–WS2 vdWHs, a nearly complete suppression of both the moiré Raman modes and the WSe2 A1g Raman mode (∼250 cm–1) is observed when exciting with a 532 nm CW laser at room temperature. Temperature-dependent reflectance contrast measurements demonstrate the significant Raman intensity modulation arises from resonant Raman effects.

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“…The second-order nonlinear optical property modulation and GBs were revealed by SHG measurements. It was also known that the twisted angle or stacking order had an impact on some other optical properties of WSe 2 . The modulation effect of other light–WSe 2 interactions were observed in the homogeneous polycrystalline stacked WSe 2 material system.…”

Section: Resultsmentioning

confidence: 95%

“…Their optical properties were evidently affected by the layer numbers and the stacking orders. It was reported that the optical responses of second-harmonic generation (SHG) and Raman scattering were strongly dependent on layer number and stacking orders of TMDC materials. − Therefore, those TMDC material systems with many quasi-periodic microstructures are useful for changing optical responses, thus modulating light–TMDC interactions. In this regard, polycrystalline TMDCs with many lattice imperfections of grain boundaries (GBs) provide an opportunity to construct a plethora of those microstructures in a crystal .…”

Section: Introductionmentioning

confidence: 99%

Chemical Vapor Deposition Growth of Homogeneous Stacked Polycrystalline WSe₂ with Branched Patterns for Modulating Light–Matter Interactions

et al. 2022

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Two-dimensional materials provide a new avenue to study light–matter interactions and have important prospects in the field of optical applications. However, electro-optic modulation ways hinged on external factors, thus restricting its direct applications. Using material with unique local microstructures to directly modulate light–matter interactions is an alternative protocol but still a challenge owing to the lack of a suitable material system. Herein, we designed a transition-metal dichalcogenide material system of homogeneous stacked polycrystalline WSe2 with branched patterns by chemical vapor deposition. Systematic characterizations indicated that the WSe2 crystals shared the key features, which consist of a large number of microstructures separated by grain boundaries. The light–WSe2 interactions are thus modulated by these isolated microstructures, where optical responses of second-harmonic generation and Raman scattering were regulated by quasi-periodic and alternating intensity fluctuation described as “enhancement quenching–enhancement quenching”. Our result reveals that constructing material systems with native polycrystalline and stacked patterns is an effective way of modulating light–matter interactions. This alternating modulation may provide a new way for the optical applications of grating a light modulator.

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Stacking-dependent optical properties in bilayer WSe₂

Abstract: The twist angle between the monolayers in van der Waals heterostructures provides a new degree of freedom in tuning material properties. We compare the optical properties of WSe2 homobilayers with...

Cited by 26 publications

References 46 publications

Nanoscale Optical Imaging of 2D Semiconductor Stacking Orders by Exciton‐Enhanced Second Harmonic Generation

Nanoscale Optical Imaging of 2D Semiconductor Stacking Orders by Exciton‐Enhanced Second Harmonic Generation

Emergent Moiré Phonons Due to Zone Folding in WSe₂–WS₂ Van der Waals Heterostructures

Chemical Vapor Deposition Growth of Homogeneous Stacked Polycrystalline WSe₂ with Branched Patterns for Modulating Light–Matter Interactions

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Stacking-dependent optical properties in bilayer WSe2

Abstract: The twist angle between the monolayers in van der Waals heterostructures provides a new degree of freedom in tuning material properties. We compare the optical properties of WSe2 homobilayers with...

Cited by 26 publications

References 46 publications

Nanoscale Optical Imaging of 2D Semiconductor Stacking Orders by Exciton‐Enhanced Second Harmonic Generation

Nanoscale Optical Imaging of 2D Semiconductor Stacking Orders by Exciton‐Enhanced Second Harmonic Generation

Emergent Moiré Phonons Due to Zone Folding in WSe2–WS2 Van der Waals Heterostructures

Chemical Vapor Deposition Growth of Homogeneous Stacked Polycrystalline WSe2 with Branched Patterns for Modulating Light–Matter Interactions

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Product

Resources

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Stacking-dependent optical properties in bilayer WSe₂

Emergent Moiré Phonons Due to Zone Folding in WSe₂–WS₂ Van der Waals Heterostructures

Chemical Vapor Deposition Growth of Homogeneous Stacked Polycrystalline WSe₂ with Branched Patterns for Modulating Light–Matter Interactions