Tungsten Selenide Research Articles

Highly sensitive near-field leakage-enhanced optical fiber SPR sensor based on gold nanoarrays modulation

A novel near-field leakage-enhanced optical fiber surface plasmon resonance (NLF-SPR) sensor based on the synergistic sensitization of cuboid gold nanoarrays and WSe2 film is proposed for the first time to our knowledge. The sensor is composed of a side-polished multimode fiber, a continuous gold film, a continuous tungsten selenide (WSe2) film, and well-arranged cuboid gold nanoarrays. The sensor leverages the high carrier mobility characteristic of the WSe2 film, the near-field leakage enhancement arising from the nanoarrays structure, and the localized electric field enhancement property introduced by nanotips to enhance the refractive index sensitivity. In order to optimize the spectral characteristic, the modulation of electric field distribution and spectral characteristic by the structural parameters of gold nanoarrays is investigated through three-dimensional (3D) finite element simulation. Results show that in the refractive index range of 1.3332–1.3432 refractive index unit (RIU), the average sensitivity of the NLF-SPR sensor can reach up to 10108 nm/RIU, and the highest sensitivity can reach up to 14692.46 nm/RIU. The average sensitivity and the highest sensitivity are 1.87 times and 2.56 times higher, respectively, than those of the side-polished fiber SPR sensor with a monolayer gold film. Furthermore, the experimental results demonstrate that the near-field leakage enhancement introduced by gold nanoarrays improves the performance of the fiber SPR sensor, resulting in a 49.3 % increment in sensitivity. The experimental results are in agreement with the trend of the simulation results. Even better performance improvements have been achieved compared to existing methods and a more flexible approach to performance tuning is provided. With the maturity and development of various nanoarray processing techniques such as focused ion beam, electron beam lithography, and nanoimprint lithography, the proposed NLF-SPR sensor has the potential to be fabricated on a large scale and is expected to be widely employed in biomedical, clinical applications, and other fields.

An ultrasensitive dual-mode stagey for 17β-estradiol assay: Photoelectrochemical and colorimetric biosensor based on a WSe2/TiO2-modified electrode coupled with nucleic acid amplification

BackgroundThe abuse of 17β-estradiol(E2) has aroused wide concern in environmental and biomedical fields, which severely affects the endocrine function of human and animals. Therefore, an ultrasensitive and accurate assay of E2 is critically important. Traditional chromatography or immunoassay techniques exhibited good sensitivity and selectivity, but expensive instruments and antibodies may pose cost and stability issues, as well as difficulties in meeting on-site detection requirements. Ultrasensitive, reliable, and on-site detection of E2 at trace level remains a challenge. Hence, developing a simple, ultrasensitive assay to simultaneously achieve accurate detection and rapid visual analysis of E2 is extremely crucial. ResultsWe developed a versatile dual-mode photoelectrochemical (PEC) and colorimetric biosensor based on isothermal nucleic acid amplification strategy for the ultrasensitive and accurate detection of E2. The method modified titanium dioxide (TiO2) with tungsten selenide (WSe2) nanoflowers to synthesize WSe2/TiO2 heterostructures as a substrate for signal amplification and nanoprobe modification. Isothermal nucleic acid amplification strategy has been proven to be a powerful tool for strong signal amplification. The presence of a target triggered the nucleic acid amplification reaction, and produced a large amount of tDNA that competed with G-quadruplex immobilized on the electrode surface. The remaining G-quadruplex/hemin catalyzed the 4-chloro-1-naphthol (4-CN) to form biocatalytic precipitation (BCP) and ABTS-H2O2 chromogenic reaction, thus, the dual-mode platform was capable of achieving PEC-colorimetric ultrasensitive detection based on the catalytic activity of G-quadruplex/hemin DNAzyme. Within optimal conditions, the dual-mode biosensor exhibited a remarkable detection limit as low as 0.026 pM. SignificanceBenefiting from the superior performance of WSe2/TiO2 and the power signal amplification of isothermal nucleic acid amplification strategy, this aptasensor achieved the ultrasensitive detection of E2. The independent transmission paths of photoelectrochemical and colorimetric provide mutual support and flexible switching, significantly enhancing the overall sensitivity and accuracy of the detection strategy, which can meet the needs for E2 precise quantification and rapid on-site detection.

Enhancing photoluminescence of WSe2 in vapor grown WSe2/VOCl bilayer heterojunctions via surface passivation.

Monolayer tungsten selenide (WSe2) has attracted attention due to its direct bandgap-generated strong light emission and light-matter interaction. Herein, vertical WSe2/VOCl bilayer heterojunctions with enhanced PL of WSe2 were synthesized by the vapor growth method. The morphology, crystal structure, and chemical composition of the WSe2/VOCl heterojunctions were systematically investigated, which confirmed the successful formation of the heterojunctions. The PL emission intensity of WSe2 obtained from the WSe2/VOCl heterojunction was about 2.4 times higher than that of the WSe2 monolayer, demonstrating the high optical quality of the WSe2/VOCl heterojunction, which was further confirmed by time-resolved PL measurements. The insulator top VOCl, which was deposited on the surface of the semiconductor bottom WSe2 as a surface passivation material, reducing the impurities and resulting in an atomically clean surface, successfully enhanced the PL emission of the bottom WSe2. This vertical WSe2/VOCl bilayer heterojunction with PL enhancement could provide a promising platform for optical devices.

Self-assembly tungsten selenide hybrid ternary MOF derived magnetic alloys via multi-polarization to boost microwave absorption

Self-assembly tungsten selenide hybrid ternary MOF derived magnetic alloys via multi-polarization to boost microwave absorption

Solution-Processed Heterojunction Photodiodes Based on WSe2 Nanosheet Networks.

Solution-processed photodetectors incorporating liquid-phase-exfoliated transition metal dichalcogenide nanosheets are widely reported. However, previous studies mainly focus on the fabrication of photoconductors, rather than photodiodes which tend to be based on heterojunctions and are harder to fabricate. Especially, there are rare reports on introducing commonly used transport layers into heterojunctions based on nanosheet networks. In this study, a reliable solution-processing method is reported to fabricate heterojunction diodes with tungsten selenide (WSe2 ) nanosheets as the optical absorbing material and PEDOT: PSS and ZnO as injection/transport-layer materials. By varying the transport layer combinations, the obtained heterojunctions show rectification ratios of up to ≈104 at ±1V in the dark, without relying on heavily doped silicon substrates. Upon illumination, the heterojunction can be operated in both photoconductor and photodiode modes and displays self-powered behaviors at zero bias.

Chemically assembled 2D-van der Waals WSe2-WC heterostructured photo-anodes for electrochemical devices

Structural, optical, nanomorphological, photoresponsive and electrochemical charge transport characteristics of chemically assembled 2D-layered Tungsten Selenide (WSe2)-Tungsten Carbide (WC) heterostructure were examined. WC exhibited an optical bandgap of ∼3.2 eV, which did not show any optical absorption in the visible spectrum, and WSe2 showed the same in the spectral range of 200 nm-950 nm with an optical bandgap of ∼1.3 eV. Chemical assembly of WSe2-WC heterostructure was made in which the weight fraction of WSe2 was varied to understand its role in WC. Among the 2, 4, 6 and 8 wt% of WSe2 in WC, we observed that 6 wt% exhibited a dominant absorption and fluorescence emission (∼600 nm). High-resolution transmission electron microscopic studies revealed the d-spacing values of 0.24 nm and 0.33 nm for WSe2 and WC, respectively. Further, the presence of W (4f), Se (2d) and C (1 s) were traced out and studied by X-ray photoelectron spectroscopy. Raman modes A1g and EAg1 at 150 cm−1 and 250 cm−1 asserted the presence of WSe2 in WC which exhibited A1g at 150 cm−1. In addition, the individual WSe2 and WC along with WSe2-WC heterostructures were subjected to X-ray diffraction to study the crystallite size and strain-induced broadening due to the lattice deformation that occurred at the WSe2-WC heterostructures. Incorporating WSe2 into WC increased the photo-responsive behaviour and facilitated the charge transport as envisaged from the electrochemical impedance spectroscopic studies.

Flexible organic-intercalated WSe2 hybrid: electronic structure modification and thermoelectric performance optimization

Two-dimensional tungsten selenide (WSe2) has great potential in thermoelectric (TE) applications, but dimensionality reduction results in a dramatic increase in thermal conductivity, which is not beneficial for improving thermoelectric performance. In this work, an electrochemical intercalation method is utilized to fabricate an organic-inorganic hybrid superlattice structure by decoupling the WSe2 layers without damaging the original bulk structure and then intercalating tetrabutylammonium (TBA) cations into the inorganic layers. The few-layer mixed-staging TBA-WSe2 hybrid with alternating stacking organic TBA cations and WSe2 inorganic layers possesses an electronic structure similar to that of the few-layer WSe2, which is beneficial for an enhanced Seebeck coefficient. The electron injection results in a considerable increase in the carrier concentration while the disorder in the mixed-staging structure succeeds in improving phonon scattering, leading to an enhanced figure-of-merit ZT of 0.25 at 340 K, which is three orders of magnitude higher than that of the pristine WSe2 single crystal and one of the highest ZT values among WSe2-based thermoelectric materials in recent years. This work may guide future research on dimensionality reduction in the electronic structures of bulk materials and the fabrication of flexible superlattice hybrids with considerable TE performance.

Two-Dimensional Materials-Based Plasmonic Sensors for Health Monitoring Systems—A Review

Two dimensional (2D) materials based plasmonic sensors are widely used in many sensing applications, particularly in biosensors due to their distinctive qualities such as label-free detection, cost-effective, and real-time monitoring. This article summarizes the advances in the 2D materials based plasmonic sensors with respect to different materials such as graphene, antimonene, phosphorene, blue phosphorous, molybdenum sulphide, molybdenum selenide, and tungsten selenide. This review also includes the comparison based on the sensitivity, detection range, and detection limit of the 2D materials-based plasmonic sensors in context to those biosensing applications. These parameters in true sense determine the sensor’s accuracy and applicability in health monitoring systems for desired results.

Reconfigurable Artificial Synapse Based on Ambipolar Floating Gate Memory.

Artificial synapse networks capable of massively parallel computing and mimicking biological neural networks can potentially improve the processing efficiency of existing information technologies. Semiconductor devices functioning as excitatory and inhibitory synapses are crucial for developing intelligence systems, such as traffic control systems. However, achieving reconfigurability between two working modes (inhibitory and excitatory) and bilingual synaptic behavior in a single transistor remains challenging. This study successfully mimics a bilingual synaptic response using an artificial synapse based on an ambipolar floating gate memory comprising tungsten selenide (WSe2)/hexagonal boron nitride (h-BN)/ molybdenum telluride (MoTe2). In this WSe2/h-BN/MoTe2 structure, ambipolar semiconductors WSe2 and MoTe2 are inserted as channel and floating gates, respectively, and h-BN serves as the tunneling barrier layer. Using either positive or negative pulse amplitude modulations at the control gate, this device with bipolar channel conduction produced eight distinct resistance states. Based on this, we experimentally projected that we could achieve 490 memory states (210 hole-resistance states + 280 electron-resistance states). Using the bipolar charge transport and multistorage states of WSe2/h-BN/MoTe2 floating gate memory, we mimicked reconfigurable excitatory and inhibitory synaptic plasticity in a single device. Furthermore, the convolution neural network formed by these synaptic devices can recognize handwritten digits with an accuracy of >92%. This study identifies the unique properties of heterostructure devices based on two-dimensional materials as well as predicts their applicability in advanced recognition of neuromorphic computing.

Selenide Heterostructure Nanosheets with Efficient Near-Infrared Photothermal Conversion for Therapy.

Photothermal therapy has been regarded as one of promising ways for tumor treatment. However, nanoagents with highly efficient thermal conversion and good bio-compatibility are still needed to be developed in biomedicine. In this work, we prepared two-dimensional heterostructures with bismuth selenide and tungsten selenide nanosheets as photothermal nanoagents. Near-infrared photothermal conversion of selenide heterostructure nanosheets can reach up to 40.75% under 808 nm excitation. It is known that selenium is a critical element to human health. More importantly, our experiments with mice show that the heterostructure nanosheets have low toxicity and high biocompatibility both in vitro and in vivo. The nanoagents based on heterostructures can effectively realize photothermal tumor ablation. It is suggested that the developed selenide nanosheets have great potential application in cancer therapy.

Dislocation-driven growth of WS2/WSe2 quantum well superlattices

The synthesis of two-dimensional lateral heterojunctions with nanoscale characteristic width and sharp interfaces remains challenging. The quantum confinement effects are still difficult to create on 2D materials since widths smaller than 5 nm are necessary for quantum confinement effects and quantum well applications. In this study, we demonstrated the growth of a sub-2-nm tungsten sulfide quantum well array in a monolayer of tungsten selenide, driven by the climb of mismatch dislocation in a heterointerface due to the lattice mismatch. Width-controllable 2D quantum well superlattices are theoretically formed by the mismatch dislocation-driven growth mechanism, according to our analysis. Thus, abundant photonic electronic properties can be obtained in 2D quantum well superlattices formed at varied lateral heterointerfaces, which will support the study of topological insulators and superconductors.

A structural study of size selected WSe2 nanoflakes prepared via liquid phase exfoliation: X-ray absorption to electrochemical application

Transition metal dichalcogenides (TMDs) have been recognised as a candidate material in many electrochemical applications including energy storage, and electrocatalyst. In the TMDs family, the molybdenum disulfide produced via liquid phase exfoliation had received attracted attention for fabricating the electrode. This is due to a clear structural and electrochemical property shown in the literature. To further explore the applications of the electrode made from TMDs materials, the tungsten selenide (WSe2) with a variety of flake sizes, and its properties were produced through a traditional liquid phase exfoliation using iso-propanol/water as an exfoliation solvent. The cascade centrifugal techniques were then applied to obtain a finely-selected flake size of WSe2 for electrochemical and physical chacterisation. In this work, we shed more light on the structural and electrocatalyst properties of the size selected WSe2. A variety of WSe2 flakes exhibit almost similar structure; however, we have found that the intensity of W L3-edge XANES spectra decreases with respect to the increase of flake dimension. This is due to the change in the electronic structure of those materials. The change directly affects the electrocatalytic performance in which, the tiny flake displayed an excellent catalytic property for hydrogen evolution reaction with the Tafel slope of 76.11 mV dec−1 and overpotential of −400 mV vs. RHE (at 10 mA cm−2). This work provides insight into the structural information, which should improve the understanding of TMDs materials in various contexts, especially electrocatalyst and energy storage.

WSe2 nanowires-based nanofluids for concentrating solar power

Tungsten selenide belongs to the family of inorganic compounds denominated transition metal dichalcogenides (TMDCs). There is emerging interest in these compounds in the field of optoelectronics, catalysis, sensing or energy storage, among others. Most works focus on the use of these materials in their 2D form but there is scarce research on the study of TMDCs nanomaterials with one-dimensional morphology. In this work, we explore the thermophysical properties of nanofluids based on 1D-WSe2 nanostructures with the aim of studying the feasibility of these nanofluids as heat transfer fluids in concentrating solar power plants. In this respect, nanofluids with a high heat transfer rate could increase the thermal efficiency of solar power plants, which would reduce the energy dependence on fossil fuels. Nanofluids of 0.02 wt%, 0.05 wt% and 0.10 wt% WSe2 concentrations have been prepared by the two-step method considering a thermal fluid used in solar power plants as the base fluid. The results of extinction coefficient evolution, ζ potential and particle size in suspension show a high colloidal stability over time of the prepared nanofluids mainly because of the high aspect ratio of the 1D-WSe2 nanomaterial. Additionally, the one-dimensionality and length of the synthesized nanowires favors the transport of heat in controlled directions, obtaining increases in thermal conductivity with respect to the base fluid of up to 16.8% in the highest concentration nanofluid. Improvements in isobaric specific heat of up to 15.7% and heat transfer of up to 20.8% compared to the base fluid have also been found. The results of this paper provide evidence that the presence of WSe2 nanowires induces increases in the thermal properties of the fluid commonly used in concentrating solar power plants without inducing agglomeration or sedimentation problems. Therefore, the nanofluids based on 1D-WSe2 nanostructures prepared in this work have a high potential to be used as heat transfer fluids in concentrating solar power plants based on parabolic trough collectors.

Unlock the Potassium Storage Behavior of Single-Phased Tungsten Selenide Nanorods via Large Cation Insertion.

Metal chalcogenide anodes with a layered structure have been regarded as potential K-based electrochemical energy storage devices with high energy density for large-scale energy storage applications. However, their development is impeded by the slow K-ion transport kinetics and poor structural stability. In this work, the energy-storage behavior is investigated first and decisively associated them with the capacity-degradation of the promising layer-structured WSe2 from an integrated chemical and physical point of view. Then, a single-phased WSe2 with pre-intercalated high K content (SP-Kx WSe2 ) is designed to overcome the capacity-degradation issue fundamentally. Theoretical calculations clarify the beneficial effect of K-ions inside the interlayer of WSe2 on boosting its electrochemical performance, including increasing the electronic conductivity, promoting the K-ion diffusivity, and improving the structural stability. The novel design enables the K-ions pre-intercalated WSe2 anode material to exhibit a high reversible specific capacity of 211 mAh g-1 at 5 A g-1 and superior cycling stability (89.3% capacity retention after 5000 cycles at 1 A g-1 ). Especially, the K-ion hybrid capacitor, assembled from the anode of SP-Kx WSe2 and the cathode of porous activated carbon, delivers superior energy-density up to 175Wh kg-1 , high power-density as well as exceptional cycling stability.

Dual-wavelength photodetector based on layered WSe2/n-GaN van der Waals heterostructure

Van der Waals (vdW) heterojunction photodetectors based on two-dimensional (2D) materials have been widely used in the field of optoelectronics. However, so far, there are few studies on 2D materials with type I energy band alignment. In this work, layered tungsten selenide (WSe2) is transferred on the prepared gallium nitride (GaN) substrate by mechanical exfoliation method. The morphology and optical properties of layered WSe2 are characterized by atomic force microscope (AFM) and spectrum. Besides, the current–voltage (I–V) characteristics, photoresponses, and transient photoresponses of the photodetector based on WSe2/GaN heterojunction are investigated, it is found that the device shows good rectifying behavior and dual-wavelength photoresponse. Furthermore, the density functional theory (DFT) calculations verify the type I energy band alignment of the WSe2/GaN heterojunction and exhibit the enhanced optical absorption corresponding to the photoresponse band. This work demonstrates that the WSe2/GaN heterojunction photodetector based on the mechanical exfoliation method holds potential for the application of optoelectronic devices.

Nano-WSe2 Is Absorbable and Transformable by Rice Plants.

As typical transition metal dichalcogenides (TMDC), tungsten selenide (WSe2) nanosheets (nano-WSe2) are widely used in various fields due to their layered structures and highly tunable electronic and magnetic properties, which results in the unwanted release of tungsten (W) and selenium (Se) into the environment. However, the environmental effects of nano-WSe2 in plants are still unclear. Herein, we evaluated the impacts and fate of nano-WSe2 and micro-WSe2 in rice plants (Oryza sativa L.). It was found that both nano-WSe2 and micro-WSe2 did not affect the germination of rice seeds up to 5000 mg/L but nano-WSe2 affected the growth of rice seedlings with shortened root lengths. The uptake and transportation of WSe2 was found to be size-dependent. Moreover, W in WSe2 was oxidized to tungstate while Se was transformed to selenocysteine, selenomethionine, SeIV and SeVI in the roots of rice when exposed to nano-WSe2, suggesting the transformation of nano-WSe2 in rice plants. The exposure to nano-WSe2 brought lipid peroxidative damage to rice seedlings. However, Se in nano-WSe2 did not contribute to the synthesis of glutathione peroxidase (GSH-Px) since the latter did not change when exposed to nano-WSe2. This is the first report on the impacts and fate of nano-WSe2 in rice plants, which has raised environmental safety concerns about the wide application of TMDCs, such as WSe2 nanosheets.

MOCVD of WSe2 crystals on highly crystalline single- and multi-layer CVD graphene

The scalable synthesis of van der Waals vertical heterostructures (vdWHs) is viewed as an important milestone for the fabrication of novel 2D-based functional applications. Combining semi-metallic graphene with semiconducting transition metal dichalcogenides (TMDs) shows great potential to explore new device architectures with unique functionalities. In this work, we investigate the gas-source metal–organic chemical vapor deposition (MOCVD) of tungsten selenide (WSe2) on highly crystalline CVD graphene. Single- and multi-layer graphene constitute interesting testing grounds for investigating fundamental WSe2 growth mechanisms owing to its atomically smooth surface, absence of dangling bonds, chemical inertness, and hexagonal lattice symmetry. Our experimental results show how the graphene template properties influence the WSe2 nucleation site density, growth rate, in-plane orientation, and thickness. In particular, we found that WSe2 growth behavior strongly depends on the number of graphene layers, their stacking order/twisting angle, as well as on the nature of the substrate underneath.

First-Principles Study of Induced Magnetism in Tungsten Vanadium Selenide Alloys for Spintronic Applications.

The possibility of inducing magnetization in tungsten selenide monolayer by alloying with vanadium selenide was investigated through first-principles calculations. Electronic, optical, and magnetic properties of different W1–xVxSe2 alloy compositions were studied extensively. As the proportion of vanadium atoms in the alloys increased, a phase transition from semiconducting to metallic to semiconducting was discovered. All alloy compositions demonstrated induced magnetism with a long-range ferromagnetic order. Interestingly, in the case of the W0.25V0.75Se2 alloy, spin-up states in the band diagram showed a finite band gap, while a nonzero band gap was found for spin-down states. The W0.25V0.75Se2 alloy can be used as a spin filter tunneling barrier exploiting this fascinating property. High spin polarization of the tunnel current was found for the alloy. Furthermore, under the Curie temperature, electrical conductivity for the spin-up channel was found to be zero, while conductivity for the spin-down channel was around 1019 (Ω cm s)−1 when the chemical potential was 0.2 eV greater than the Fermi energy. Changes in optical properties were also investigated through time-dependent density functional theory calculations. The findings of this study will be beneficial for proposing new magnetic monolayer alloys for application in nanoscale spintronic devices.

Low temperature CVD growth of WSe2 enabled by moisture-assisted defects in the precursor powder

Two-dimensional transition metal dichalcogenides (TMDs) have been proposed for a wide variety of applications, such as neuromorphic computing, flexible field effect transistors, photonics, and solar cells, among others. However, for most of these applications to be feasible, it is necessary to integrate these materials with the current existing silicon technology. Although chemical vapor deposition is a promising method for the growth of high-quality and large-area TMD crystals, the high temperatures necessary for the growth make this technique incompatible with the processes used in the semiconductor industry. Herein, we demonstrate the possibility of low-temperature growth of TMDs, using tungsten selenide (WSe2) as a model, by simply using moisture-assisted defective tungsten oxide (WO3) precursor powders during the growth of these materials. Density functional theory calculations reveal the mechanism by which moisture promotes the defect formation on the precursor crystal structure and how it dictates the reduction of the temperature of the growth. The results were compared with the standard growth at high temperatures and with a precursor mixture with alkali salts to show the high quality of the WSe2 grown at temperatures as low as 550 °C. To conclude, the work improves the understanding of nucleation and growth mechanisms of WSe2 at low temperatures and provides a useful strategy for the growth of TMDs at temperatures required for the back-end-of-line compatibility with current silicon technology.

(Digital Presentation) Interface Engineering of Transition Metal-Selenide Heterostructures for Application in Electrochemical Water-Splitting

Transition metal selenides (TMS) have sparked great interest in energy storage and catalysis because they are direct bandgap materials, have a highly layered structure, high redox activity, abundant active sites at the edges, short diffusion paths, and large surface area1. However, low electrical conductivity and structural instability result in long-term performance degradation. The development of high-performance water electrolyzers and metal-air batteries requires the design and construction of efficient TMS electrocatalysts. In order to boost electrochemical activity, increasing emphasis has been devoted to interface engineering of TMS heterostructures through manipulation of composition, adjustment of crystal facets, and heteroatomic doping2. Interface engineering helps in optimizing reaction intermediates, modulating charge carrier characteristics, and preventing the aggregation of active components. Herein, we designed and studied the interface between hydrothermally synthesized tin selenide (SnSe2) and tungsten selenide (WSe2). The intimate electronic interaction between the bimetallic selenides leads to a rich interface boundary that reduces the surface energy and creates a larger number of active sites involved in both the hydrogen evolution and oxygen evolution reactions3. These heterostructures exhibited a low overpotential of 180 mV at 10 mA cm-2 and good stability of up to 12 hours for the hydrogen evolution reaction, and a low overpotential of 250 mV at 10 mA cm-2 and stability up to 12 hours for the oxygen evolution reaction. This study gives a better insight into the design of TMS heterostructures using interface engineering for high electrocatalytic activity.