Ultrastable tip-enhanced hyperspectral optical nanoimaging for defect analysis of large-sized WS2 layers.
Ontology highlight
ABSTRACT:
SUBMITTER: Kato R
PROVIDER: S-EPMC9286508 | biostudies-literature |
REPOSITORIES: biostudies-literature
Similar Datasets
Project description:Identifying and fabricating defect qubits in two-dimensional semiconductors are of great interest in exploring candidates for quantum information and sensing applications. A milestone has been recently achieved by demonstrating that single defect, a carbon atom substituting sulphur atom in single layer tungsten disulphide, can be engineered on demand at atomic size level precision, which holds a promise for a scalable and addressable unit. It is an immediate quest to reveal its potential as a qubit. To this end, we determine its electronic structure and optical properties from first principles. We identify the fingerprint of the neutral charge state of the defect in the scanning tunnelling spectrum. In the neutral defect, the giant spin-orbit coupling mixes the singlet and triplet excited states with resulting in phosphorescence at the telecom band that can be used to read out the spin state, and coherent driving with microwave excitation is also viable. Our results establish a scalable qubit in a two-dimensional material with spin-photon interface at the telecom wavelength region.
| S-EPMC8904548 | biostudies-literature
Project description:Breaking the valley degeneracy in monolayer transition metal dichalcogenides through the valley-selective optical Stark effect (OSE) can be exploited for classical and quantum valleytronic operations such as coherent manipulation of valley superposition states. The strong light-matter interactions responsible for the OSE have historically been described by a two-level dressed-atom model, which assumes noninteracting particles. Here we experimentally show that this model, which works well in semiconductors far from resonance, does not apply for excitation near the exciton resonance in monolayer WS2. Instead, we show that an excitonic model of the OSE, which includes many-body Coulomb interactions, is required. We confirm the prediction from this theory that many-body effects between virtual excitons produce a dominant blue-shift for photoexcitation detuned from resonance by less than the exciton binding energy. As such, we suggest that our findings are general to low-dimensional semiconductors that support bound excitons and other many-body Coulomb interactions.
| S-EPMC6895111 | biostudies-literature
Project description:Catalyst layers in proton exchange membrane fuel cells consist of platinum-group-metal nanocatalysts supported on carbon aggregates, forming a porous structure through which an ionomer network percolates. The local structural character of these heterogeneous assemblies is directly linked to the mass-transport resistances and subsequent cell performance losses; its three-dimensional visualization is therefore of interest. Herein we implement deep-learning-aided cryogenic transmission electron tomography for image restoration, and we quantitatively investigate the full morphology of various catalyst layers at the local-reaction-site scale. The analysis enables computation of metrics such as the ionomer morphology, coverage and homogeneity, location of platinum on the carbon supports, and platinum accessibility to the ionomer network, with the results directly compared and validated with experimental measurements. We expect that our findings and methodology for evaluating catalyst layer architectures will contribute towards linking the morphology to transport properties and overall fuel cell performance. The catalyst layer in proton-exchange membrane fuel cells involves the complex and crucial interplay between an ionomer network and metallic nanoparticles supported on carbons, but current methods are unable to describe it with high resolution. Now electron tomography at cryogenic temperatures and deep learning algorithms are used to provide quantitative three-dimensional imaging at nanometre resolution of a fuel cell catalyst layer structure.
| S-EPMC10212762 | biostudies-literature
Project description:The rise of atomically thin materials has the potential to enable a paradigm shift in modern technologies by introducing multi-functional materials in the semiconductor industry. To date the growth of high quality atomically thin semiconductors (e.g. WS2) is one of the most pressing challenges to unleash the potential of these materials and the growth of mono- or bi-layers with high crystal quality is yet to see its full realization. Here, we show that the novel use of molecular precursors in the controlled synthesis of mono- and bi-layer WS2 leads to superior material quality compared to the widely used direct sulfidization of WO3-based precursors. Record high room temperature charge carrier mobility up to 52 cm2/Vs and ultra-sharp photoluminescence linewidth of just 36 meV over submillimeter areas demonstrate that the quality of this material supersedes also that of naturally occurring materials. By exploiting surface diffusion kinetics of W and S species adsorbed onto a substrate, a deterministic layer thickness control has also been achieved promoting the design of scalable synthesis routes.
| S-EPMC5668258 | biostudies-literature
Project description:Excitons dominate the light absorption and re-emission spectra of monolayer transition-metal dichalcogenides (TMD). Microscopic investigations of the excitonic response in TMD almost invariably extract information from the radiative recombination step, which only constitutes one part of the picture. Here, by exploiting imaging spectroscopic ellipsometry (ISE), we investigate the spatial dependence of the dielectric function of chemical vapor deposition (CVD)-grown WS2 flakes with a microscopic lateral resolution, thus providing information about the spatially varying, exciton-induced light absorption in the monolayer WS2. Comparing the ISE results with imaging photoluminescence spectroscopy data, the presence of several correlated features was observed, along with the unexpected existence of a few uncorrelated characteristics. The latter demonstrates that the exciton-induced absorption and emission features are not always proportional at the microscopic scale. Microstructural modulations across the flakes, having a different influence on the absorption and re-emission of light, are deemed responsible for the effect.
| S-EPMC8411805 | biostudies-literature
Project description:Exciton-polaritons (EPs) can be formed in transition metal dichalcogenide (TMD) multilayers sustaining optical resonance modes without any external cavity. The self-hybridized EP modes are expected to depend on the TMD thickness, which directly determines the resonance wavelength. Exfoliated WS2 flakes were prepared on SiO2/Si substrates and template-stripped ultraflat Au layers, and the thickness dependence of their EP modes was compared. For WS2 flakes on SiO2/Si, the minimum flake thickness to exhibit exciton-photon anticrossing was larger than 40 nm. However, for WS2 flakes on Au, EP mode splitting appeared in flakes thinner than 10 nm. Analytical and numerical calculations were performed to explain the distinct thickness-dependence. The phase shifts of light at the WS2/Au interface, originating from the complex Fresnel coefficients, were as large as π/2 at visible wavelengths. Such exceptionally large phase shifts allowed the optical resonance and resulting EP modes in the sub-10-nm-thick WS2 flakes. This work helps us to propose novel optoelectronic devices based on the intriguing exciton physics of TMDs.
| S-EPMC9319842 | biostudies-literature
Project description:Nanolight sources, which are based on resonant excitation of plasmons near a sharp metallic nanostructure, have attracted tremendous interest in the vast research fields of optical nanoimaging. However, being a resonant phenomenon, this ideally works only for one wavelength that resonates with the plasmons. Multiple wavelengths of light in a broad range confined to one spot within a nanometric volume would be an interesting form of light, useful in numerous applications. Plasmon nanofocusing can generate a nanolight source through the propagation and adiabatic compressions of plasmons on a tapered metallic nanostructure, which is independent of wavelength, as it is based on the propagation, rather than resonance, of plasmons. Here, we report the generation of a white nanolight source spanning over the entire visible range through plasmon nanofocusing and demonstrate spectral bandgap nanoimaging of carbon nanotubes. Our experimental demonstration of the white nanolight source would stimulate diverse research fields toward next-generation nanophotonic technologies.
| S-EPMC7269664 | biostudies-literature
Project description:Holography has paved the way for phase imaging in a variety of wide-field techniques, including electron, X-ray and optical microscopy. In scanning optical microscopy, however, the serial fashion of image acquisition seems to challenge a direct implementation of traditional holography. Here we introduce synthetic optical holography (SOH) for quantitative phase-resolved imaging in scanning optical microscopy. It uniquely combines fast phase imaging, technical simplicity and simultaneous operation at visible and infrared frequencies with a single reference arm. We demonstrate SOH with a scattering-type scanning near-field optical microscope (s-SNOM) where it enables reliable quantitative phase-resolved near-field imaging with unprecedented speed. We apply these capabilities to nanoscale, non-invasive and rapid screening of grain boundaries in CVD-grown graphene, by recording 65 kilopixel near-field images in 26 s and 2.3 megapixel images in 13 min. Beyond s-SNOM, the SOH concept could boost the implementation of holography in other scanning imaging applications such as confocal microscopy.
| S-EPMC4072026 | biostudies-literature
Project description:The interplay between excitons and phonons governs the optical and electronic properties of transition metal dichalcogenides (TMDs). Even though a number of linear and nonlinear optical-, electron-, and photoelectron-based approaches have been developed and/or adopted to characterize excitons and phonons in single/few-layer TMDs and their heterostructures, no existing method is capable of directly probing ultralow-frequency and interlayer phonons on the nanoscale. To this end, we developed ultralow-frequency tip-enhanced Raman spectroscopy, which allows spectrally and spatially resolved chemical and structural nanoimaging of WSe2/WS2 heterostructures. In this work, we apply this method to analyze phonons in nanobubbles that are sustained in these heterobilayers. Our method is capable of directly probing interlayer (de)coupling using our novel structurally sensitive nano-optical probe and the interplay between excitons and interlayer/intralayer phonons through correlation analysis of the recorded spectral images.
| S-EPMC9335877 | biostudies-literature
Project description:Two-dimensional (2D) materials beyond graphene such as transition metal dichalcogenides (TMDs) have unique mechanical, optical and electronic properties with promising applications in flexible devices, catalysis and sensing. Optical imaging of TMDs using photoluminescence and Raman spectroscopy can reveal the effects of structure, strain, doping, edge states, and surface functionalization from materials to bioscience. However, Raman signals are inherently weak and so far have been limited in spatial resolution in TMDs to a few hundred nanometres which is much larger than the intrinsic scale of these effects. Here we overcome the diffraction limit by using resonant tip-enhanced Raman scattering (TERS) of few-layer MoS2, and obtain nanoscale optical images with ~20 nm spatial resolution. This becomes possible due to electric field enhancement in an optimized subnanometre-gap resonant tip-substrate configuration. We investigate the limits of signal enhancement by varying the tip-sample gap with sub-Angstrom precision and observe a quantum quenching behavior, as well as a Schottky-Ohmic transition, for subnanometre gaps, which enable surface mapping based on this new contrast mechanism. This quantum regime of plasmonic gap-mode enhancement with a few nanometre thick MoS2 junction may be used for designing new quantum optoelectronic devices and sensors with a wide range of applications.
| S-EPMC4879532 | biostudies-literature