An official website of the United States government
Abstract Electronic and optoelectronic applications of two-dimensional (2D) semiconductors demand precise control over material quality, including thickness, composition, doping, and defect density. Conventional benchmarking methods (e.g. charge transport, confocal mapping, electron or scanning probe microscopy) are slow, perturb sample quality, or involve trade-offs between speed, resolution, and scan area. To accelerate assessment of 2D semiconductors, we demonstrate a broadband, wide-field hyperspectral optical microscope for 2D materials that rapidly captures a spatial-spectral data cube within seconds. The data cube includesx–yspatial coordinate (a 300 × 300µm2field, with ∼1µm resolution) and a selectable wavelength range between 200 nm to 1100 nm at each pixel. Using synthesized films and heterostructures of transition metal dichalcogenides (MoS2, WS2, VxW1−xS2, and WSe2), we show that this cost-effective technique detects spectral fingerprints of material identity, doping, grain boundaries, and alloy composition, and enables advanced analysis, including unsupervised machine learning for spatial segmentation.
more »
« less
This content will become publicly available on February 1, 2027
Excitonic Landscapes in Monolayer Lateral Heterostructures Revealed by Unsupervised Machine Learning
Abstract Two‐dimensional (2D) in‐plane heterostructures including compositionally graded alloys and lateral heterostructures with defined interfaces display rich optoelectronic properties and offer versatile platforms to explore one‐dimensional (1D) interface physics and many‐body interaction effects. Graded MoxW1 −xS2alloys show smooth spatial variations in composition and strain that continuously tune excitonic emission, while MoS2–WS2lateral heterostructures contain atomically sharp interfaces supporting 1D excitonic phenomena. These single‐layer systems combine tunable optical and electronic properties with potential for stable, high‐performance optoelectronic devices. Hyperspectral and nano‐resolved photoluminescence (PL) imaging enable spatial mapping of optical features along with local variations in composition, strain, and defects, but manual interpretation of such large datasets is slow and subjective. Here, a fast and scalable unsupervised machine‐learning (ML) framework is introduced to extract quantitative and interpretable information from hyperspectral PL datasets of graded MoxW1 −xS2alloys and MoS2–WS2heterostructures. Combining principal‐component analysis (PCA), t‐distributed stochastic neighbor embedding (t‐SNE), and density‐based spatial clustering of applications with noise (DBSCAN), spectrally distinct domains associated with composition, strain, and defect variations are uncovered. Decomposition of representative spectra reveals multiple emission species, including band‐edge excitons and defect‐related transitions, demonstrating that ML‐driven analysis provides a robust and automated route to interpret rich optical properties of 2D materials.
more »
« less
- Award ID(s):
- 2152159
- PAR ID:
- 10693251
- Publisher / Repository:
- Wiley Advanced
- Date Published:
- Journal Name:
- Advanced Optical Materials
- Volume:
- 14
- Issue:
- 7
- ISSN:
- 2195-1071
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Abstract In this work, we explore how the optical properties of isotropic materials can be modulated by adjacent anisotropic materials, providing new insights into anisotropic light-matter interactions in van der Waals heterostructures. Using a WS2/ReS2heterostructure, we systematically investigated the excitation angle-dependent photoluminescence (PL), differential reflectance, time-resolved PL, and power-dependent PL anisotropy of WS2. Our findings reveal that the anisotropic optical response of WS2, influenced by the crystallographically low symmetry and unique dielectric environment of ReS2, significantly impacts both the optical and temporal behavior of WS2. We observed that the emission anisotropy increases with optical power density, highlighting that anisotropic localization of photo-generated carriers and subsequent charge transfer dynamics are key contributors to the polarization-sensitive optical response. These findings provide a framework for leveraging optical density-sensitive anisotropy mirroring to design advanced anisotropic optoelectronic and photonic devices.more » « less
-
In this contribution, we use heavy ion irradiation and photoluminescence (PL) spectroscopy to demonstrate that defects can be used to tailor the optical properties of two-dimensional molybdenum disulfide (MoS 2 ). Sonicated MoS 2 flakes were deposited onto Si/SiO 2 substrate and subjected to 3 MeV Au 2+ ion irradiation at room temperature to fluences ranging from 1 × 10 12 to 1 × 10 16 cm −2 . We demonstrate that irradiation-induced defects can control optical excitations in the inner core shell of MoS 2 by binding A 1s - and B 1s -excitons, and correlate the exciton peaks to the specific defects introduced with irradiation. The systematic increase of ion fluence produced different defect densities in MoS 2 , which were estimated using B/A exciton ratios and progressively increased with ion fluence. We show that up to the fluences of 1 × 10 14 cm −2 , the MoS 2 lattice remains crystalline and defect densities can be controlled, whereas at higher fluences (≥1 × 10 15 cm −2 ), the large number of introduced defects distorts the excitonic structure of the material. In addition to controlling excitons, defects were used to split bound and free trions, and we demonstrate that at higher fluences (1 × 10 15 cm −2 ), both free and bound trions can be observed in the same PL spectrum. Most importantly, the lifetimes of these states exceed trion and exciton lifetimes in pristine MoS 2 , and PL spectra of irradiated MoS 2 remains unchanged weeks after irradiation experiments. Thus, this work demonstrated the feasibility of engineering novel optical behaviors in low-dimensional materials using heavy ion irradiation. The insights gained from this study will aid in understanding the many-body interactions in low-dimensional materials and may ultimately be used to develop novel materials for optoelectronic applications.more » « less
-
Abstract Nanohybrids based on van der Waals (vdW) heterostructures of two dimensional (2D) atomic materials have recently emerged as a unique scheme for designing high‐performance quantum sensors. This work explores vdW nanohybrids for photodetection, which consist of graphene decorated with intermingled transition‐metal dichalcogenide (TMDC) nanodiscs (TMDC‐NDs) obtained using wafer‐size, layer‐by‐layer growth. The obtained TMDC‐NDs/graphene nanohybrids take advantage of strong quantum confinement in graphene for high charge mobility and hence high photoconductive gain, and localized surface plasmonic resonance (LSPR) enabled on the TMDC‐NDs for enhanced light absorption. Since the LSPR depends on the nanostructure's size and density, intermingled TMDC‐NDs of different kinds of TMDCs, such as WS2(W) and MoS2(M), have been found to allow small‐size, high‐concentration TMDC‐NDs to be achieved for high photoresponse. Remarkably, high photoresponsivity up to 31 A/W (550 nm wavelength and 20 µW cm−2light intensity) has been obtained on the WMW‐NDs/graphene nanohybrids photodetectors made using three consecutive coatings of WS2(1st and 3rd coating) and MoS2(2nd coating), which is considerably higher by a factor of ≈4 than that of the counterparts MoS2‐ND/graphene or WS2‐NDs/graphene devices. This result provides a facile approach to control the size and concentration of the TMDC‐NDs for high‐performance, low‐cost optoelectronic device applications.more » « less
-
Excitons can be trapped by moiré potentials in van der Waals (vdW) heterostructures, forming ordered arrays of quantum dots. Excitons can also be trapped by defect potentials as single photon emitters. While the moiré and defect potentials in vdW heterostructures have been studied separately, their interplay remains largely unexplored. Here, we perform first-principles calculations to elucidate the interplay of the two potentials in determining the optoelectronic properties of twisted MoS 2 /WS 2 heterobilayers. The binding energy, charge density, localization, and hybridization of the moiré excitons can be modulated by the competition and cooperation of the two potentials. Their interplay can also be tuned by vertical electric fields, which can either de-trap the excitons or strongly localize them. One can further tailor the interplay of the two potentials via defect engineering to create one-dimensional exciton lattices with tunable orientations. Our work establishes defect engineering as a promising strategy to realize on-demand optoelectronic responses.more » « less
