Transition Metal Dichalcogenide Nanosheets Research Articles

Elucidating Local Structure and Positional Effect of Dopants in Colloidal Transition Metal Dichalcogenide Nanosheets for Catalytic Hydrogenolysis.

Tailoring nanoscale catalysts to targeted applications is a vital component in reducing the carbon footprint of industrial processes; however, understanding and controlling the nanostructure influence on catalysts is challenging. Molybdenum disulfide (MoS2), a transition metal dichalcogenide (TMD) material, is a popular example of a nonplatinum-group-metal catalyst with tunable nanoscale properties. Doping with transition metal atoms, such as cobalt, is one method of enhancing its catalytic properties. However, the location and influence of dopant atoms on catalyst behavior are poorly understood. To investigate this knowledge gap, we studied the influence of Co dopants in MoS2 nanosheets on catalytic hydrodesulfurization (HDS) through a well-controlled, ligand-directed, tunable colloidal doping approach. X-ray absorption spectroscopy and density functional theory calculations revealed the nonmonotonous relationship between dopant concentration, location, and activity in HDS. Catalyst activity peaked at 21% Co:Mo as Co saturates the edge sites and begins basal plane doping. While Co prefers to dope the edges over basal sites, basal Co atoms are demonstrably more catalytically active than edge Co. These findings provide insight into the hydrogenolysis behavior of doped TMDs and can be extended to other TMD materials.

Emergence of electrochemical catalytic activity via an electrochemical-probe on defective transition metal dichalcogenide nanosheets

Two-dimensional transition metal dichalcogenides (2D TMDs) have shown exceptional electrochemical catalytic activity for the efficient generation of hydrogen through electrochemical water splitting. In the case of molybdenum disulfide (MoS2), a prominent member of 2D TMDs, the electrochemically active sites primarily reside at the edges, while the basal plane, which constitutes the majority of the MoS2 structure, remains relatively inactive. In this study, we aimed to activate the inert sites of the basal plane with some defective structure for hydrogen evolution reaction (HER) by employing an electrochemical-probe in combination with voltage sweeping. The initiation of HER at these previously inactive sites was visualized and confirmed using scanning electrochemical cell microscopy (SECCM). Our findings reveal that the enhanced HER activity originates from surface defects induced by the probing process.

Chemical vapor deposition growth of graphene and other nanomaterials with 3D architectures towards electrocatalysis and secondary battery-related applications.

Recently, two-dimensional (2D) layered materials, such as graphene and transition metal dichalcogenides (TMDCs), have garnered a lot of attention in energy storage/conversion-related fields due to their novel physical and chemical properties. Constructing flat graphene and TMDCs nanosheets into 3D architectures can significantly increase their exposed surface area and prevent the restacking of adjacent 2D layers, thus dramatically promoting their applications in various energy-related fields. Chemical Vapor Deposition (CVD) is a low-cost, facile, and scalable method, which has been widely employed to produce high-quality graphene and TMDCs nanosheets with 3D architectures. During the CVD process, the morphologies and properties of the 3D architectures of such 2D materials can be designed by selecting substrates with different compositions, stacking geometries, and micro-structures. In this review, we focus on the recent advances in the CVD synthesis of graphene, TMDCs, and their hybrids with 3D architectures on different 3D-structured substrates, as well as their applications in the electrocatalytic hydrogen evolution reaction (HER) and various secondary batteries. In addition, the challenges and future prospects for the CVD synthesis and energy-related applications of these unique layered materials will also be discussed.

Composition-tunable transition metal dichalcogenide nanosheets via a scalable, solution-processable method.

The alloying of two-dimensional (2D) transition metal dichalcogenides (TMDs) is an established route to produce robust semiconductors with continuously tunable optoelectronic properties. However, typically reported methods for fabricating alloyed 2D TMD nanosheets are not suitable for the inexpensive, scalable production of large-area (m2) devices. Herein we describe a general method to afford large quantities of compositionally-tunable 2D TMD nanosheets using commercially available powders and liquid-phase exfoliation. Beginning with Mo(1-x)WxS2 nanosheets, we demonstrate tunable optoelectronic properties as a function of composition. We extend this method to produce Mo0.5W0.5Se2 MoSSe, WSSe, and quaternary Mo0.5W0.5SSe nanosheets. High-resolution scanning transmission electron microscopy (STEM) imaging confirms the atomic arrangement of the nanosheets, while an array of spectroscopic techniques is used to characterize the chemical and optoelectronic properties. This transversal method represents an important step towards upscaling tailored TMD nanosheets with a broad range of tunable optoelectronic properties for large-area devices.

Fabrication of amorphous subnanometric palladium nanostructures on metallic transition metal dichalcogenides for efficient hydrogen evolution reaction

Metallic transition metal dichalcogenide nanosheets decorated with amorphous subnanometric Pd nanoparticles exhibit comparable HER performance to that of commercial Pt–C.

Recent Strategies for the Synthesis of Phase-Pure Ultrathin 1T/1T' Transition Metal Dichalcogenide Nanosheets.

The past few decades have witnessed a notable increase in transition metal dichalcogenide (TMD) related research not only because of the large family of TMD candidates but also because of the various polytypes that arise from the monolayer configuration and layer stacking order. The peculiar physicochemical properties of TMD nanosheets enable an enormous range of applications from fundamental science to industrial technologies based on the preparation of high-quality TMDs. For polymorphic TMDs, the 1T/1T' phase is particularly intriguing because of the enriched density of states, and thus facilitates fruitful chemistry. Herein, we comprehensively discuss the most recent strategies for direct synthesis of phase-pure 1T/1T' TMD nanosheets such as mechanical exfoliation, chemical vapor deposition, wet chemical synthesis, atomic layer deposition, and more. We also review frequently adopted methods for phase engineering in TMD nanosheets ranging from chemical doping and alloying, to charge injection, and irradiation with optical or charged particle beams. Prior to the synthesis methods, we discuss the configuration of TMDs as well as the characterization tools mostly used in experiments. Finally, we discuss the current challenges and opportunities as well as emphasize the promising fields for the future development.

Trapping and exciton-exciton annihilation assisted ultrafast carrier dynamics in nanosheets of 2H-MoSe2 and Cr doped 1T/2H-MoSe2.

Nanosheets of transition metal dichalcogenides with prospects of photocatalysis and optoelectronics applications have significant potential in device fabrication due to their low-cost production and easily controllable morphology. Here, non-degenerate pump-probe differential transmission studies with varying pump-fluence have been carried out on single-phase 2H-MoSe2 and mixed-phase 1T/2H-MoSe2 nanosheets to characterize their excited carrier dynamics. For both the samples, the differential probe transmission data show photo-induced bleaching at earlier pump-probe delay followed by photo-induced absorption unveiling signatures of exciton-state filling, exciton trapping, defect-mediated photo-induced probe absorption and recombination of defect bound excitons. The exciton trapping and photo-induced absorption by the trapped-carriers are estimated to occur with time constant of ∼430 to 500fs based on multi-exponential modelling of the differential transmission till pump-probe delay of ∼3.5ps. Biexponential modeling of the subsequent slow-recovery of the negative differential transmission at pump-probe delay ≳3.5ps reveals that the exciton recombination happens via two distinct decay channels with ∼25 to 55ps (τ1) and ≳1ns (τ2) time constants. Pump-fluence dependent reduction in τ1 and further modelling of exciton population using higher order kinetic rate equation reveals that the two-body exciton-exciton annihilation governs the exciton recombination initially with a decay rate of ∼10-8 cm3s-1. The detailed analysis suggests that the fraction of total excitons that decay via long decay channel decreases with increasing exciton density for 2H-MoSe2, in contrast to 1T/2H-MoSe2 where the fraction of excitons decaying via long decay channel remains constant.

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.

Ecotoxicological assessment of water phase exfoliated two-dimensional Group-VI transition metal dichalcogenides using zebrafish embryo model

Among emerging layered materials, 2D transition metal dichalcogenides (TMDs) nanosheets (n-sheets) have received increasing attention for optoelectronics, energy storage, and, recently, for bioremediation and advanced biomedical applications; however, a lack of ecotoxicological in vivo studies is evident. Herein, for the first time, the potential nanotoxicity of liquid phase exfoliated Group VI TMDs n-sheets (MoS2, WS2, WSe2, and MoSe2) was comparatively investigated using zebrafish embryos (Z-EBs) as an in-vivo model. The 2D n-sheets were produced directly in aqueous-medium, the obtained n-sheets were characterized by scanning electron microscopy, Raman and visible spectroscopy, and their potential nanotoxicity was investigated by fish embryo test OECD TG 236. Chorionated and dechorionated embryos were used to assess the severity of TMD exposure. The survival rate, sublethal alteration during embryogenesis, hatching rate, and mortality were evaluated. TMDs n-sheets tend to adhere to the Z-EBs surface depending on their chemistry. Despite this, TMDs did not show lethal effects; weak sublethal effects were found for MoS2 and WSe2, while slight hatching delays were registered for MoSe2 and WSe2. The observed effects are attributable to the TMDs' tendency to interact with Z-EBs, because of the different chemistry. This work demonstrates how water-dispersed TMDs are potential eco/biocompatible materials.

Synthesis and Formulation of Ternary Transition Metal Dichalcogenide Alloys for Additive Electronic Manufacturing

Compared with the most investigated graphene, layered transition metal dichalcogenides (TMDs) have received significant attention due to their various chemical compositions and great potential electronic application. In order to tailor and engineer properties of TMDs and therefore enhance their efficiency toward commercial applications, several methods have been employed including reducing dimensionality, creating inter and intra-heterostructures, introducing inter stain, and alloying. Among these, alloying via chemical vapor transport (CVT) is scalable, cost- efficient, and controllable method of tuning TMD bulk crystal properties. Alloying of TMDs can be categorized into several types including metal replacement, dichalcogenide replacement, and both metal and dichalcogenide replacement. In a typical TMD CVT reaction, high-purity precursors are mixed in a desired stochiometric ratio, vacuumed, and sealed in an ampoule to form a closed system. The resulting TMD crystal can then be used for additional processes, e.g., exfoliation to yield 2D TMD nanosheets. Additive electronics manufacturing is a promising technique for the scalable fabrication of electronic devices, including sensors and energy storage devices. For an ink to be compatible for different printing modalities the ink rheology including viscosity, surface tension, and solid requires to be tuned to obtain suitable fluid dynamic parameters for jetting the ink. This work summarizes the development, synthesis, characterization, and formulation of two-dimensional ternary TMDCs ink for aerosol jet printing (AJP) technology. Ball milling assisted liquid exfoliation is utilized for synthesizing ternary TMDs nanomaterials under controlled condition. The resulting nanomaterial is developed into nanomaterial ink compatible with AJP. Detailed analysis of the material characterization and ink properties are required to optimize the fluid dynamics and properties of the ink. After printing the formulated ink using AJP on various substrates, post-printing process techniques is required to be investigated for printed nanomaterials inks to achieve bulk-like performance for the printed structures. Our results highlight the innovations in synthesis and formulation of ternary transition metal dichalcogenide nanomaterial inks for additive manufacturing of electronic devices such as sensors, solar cells, and energy storage devices.

Transition Metal Dichalcogenides Nanoscrolls: Preparation and Applications.

Two-dimensional (2D) transition metal dichalcogenides (TMDCs) nanosheets have shown extensive applications due to their excellent physical and chemical properties. However, the low light absorption efficiency limits their application in optoelectronics. By rolling up 2D TMDCs nanosheets, the one-dimensional (1D) TMDCs nanoscrolls are formed with spiral tubular structure, tunable interlayer spacing, and opening ends. Due to the increased thickness of the scroll structure, the light absorption is enhanced. Meanwhile, the rapid electron transportation is confined along the 1D structure. Therefore, the TMDCs nanoscrolls show improved optoelectronic performance compared to 2D nanosheets. In addition, the high specific surface area and active edge site from the bending strain of the basal plane make them promising materials for catalytic reaction. Thus, the TMDCs nanoscrolls have attracted intensive attention in recent years. In this review, the structure of TMDCs nanoscrolls is first demonstrated and followed by various preparation methods of the TMDCs nanoscrolls. Afterwards, the applications of TMDCs nanoscrolls in the fields of photodetection, hydrogen evolution reaction, and gas sensing are discussed.

Gum Arabic-mediated liquid exfoliation of transition metal dichalcogenides as photothermic anti-breast cancer candidates

Transition metal dichalcogenides (TMDs) have gained considerable attention for a broad range of applications, including cancer therapy. Production of TMD nanosheets using liquid exfoliation provides an inexpensive and facile route to achieve high yields. In this study, we developed TMD nanosheets using gum arabic as an exfoliating and stabilizing agent. Different types of TMDs, including MoS2, WS2, MoSe2, and WSe2 nanosheets, were produced using gum arabic and were characterized physicochemically. The developed gum arabic TMD nanosheets exhibited a remarkable photothermal absorption capacity in the near-infrared (NIR) region (808 nm and 1 W⋅cm−2). The drug doxorubicin was loaded on the gum arabic–MoSe2 nanosheets (Dox–G–MoSe2), and the anticancer activity was evaluated using MDA-MB-231 cells and a water-soluble tetrazolium salt (WST-1) assay, live and dead cell assays, and flow cytometry. Dox–G–MoSe2 significantly inhibited MDA-MB-231 cancer cell proliferation under the illumination of an NIR laser at 808 nm. These results indicate that Dox-G-MoSe2 is a potentially valuable biomaterial for breast cancer therapy.

Preparation and photothermal effect of Chitosan-Alginate-Molybdenum diselenide nanocomposite scaffolds for cancer therapy

Transition metal dichalcogenides (TMDs) have gained significant attention for biological and biomedical applications due to their biocompatible properties and photothermal effects. In the current study, TMD nanosheets were fabricated with poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol) (PPP) triblock copolymer using the liquid exfoliation method. This study prepared TMD nanosheets of PPP-molybdenum sulfide (PPP-MoS2), PPP-tungsten disulfide (PPP-WS2), PPP-molybdenum diselenide (PPP-MoSe2), and PPP-tungsten diselenide (PPP-WS2). The synthesized PPP-TMD nanosheets were characterized using DLS, FT-IR, XRD, SEM, TEM, XPS, and photothermal studies. The DLS results indicated that the nanosheets were 165.1 ± 2.2 to 217.7 ± 2.8 nm and had a zeta potential of −40.9 ± 0.6 to −43.3 ± 0.4 mV and a polydispersity index (PDI) of 0.2. The FT-IR results showed that the fabricated nanosheets contained polymeric substances, and the UV results confirmed that each PPP-TMD had surface plasmon resonance peaks. The XRD patterns of the nanosheets were consistent with those of the International Centre for Diffraction Data. The SEM and TEM results determined that the PPD-TMD sheets were 150 ± 20 nm wide and were single-layer nanosheets with selective area diffraction patterns. The photothermal effects of the PPP-MoSe2 nanosheets at a 30 µg/mL concentration were evaluated at 808 nm with a 1 W cm−2 current. PPP-MoSe2 exhibited the strongest photothermal effect at > 55 °C for 5 min of laser exposure. In addition, the cytotoxicity effects of PPP-MoSe2 were measured with breast cancer cells (MDA-MB-231) with a 5 min laser treatment. At a 30 µg/mL concentration, PPP-MoSe2 inhibited cancer cells by up to 95 %. Further, alginate-chitosan-PPP-MoSe2 composites were developed and evaluated for their photothermal effect. We believe that PPP-MoSe2 will be an excellent material in cancer therapy.

Van der waals epitaxial growth of mixed-dimensional 1D/2D heterostructures with tellurium nanowires and transition metal dichalcogenide nanosheets for nonlinear optical applications

One-dimensional (1D) tellurium (Te) nanowires (NWs) have triggered intense attention due to their remarkable properties in electronics, optoelectronics and nonlinear optics. However, the saturable absorption properties of Te NWs and the ability to be bleached by strong pulsed energy need to be further improved. Van der Waals (vdW) heterostructures based on two-dimensional (2D) transition metal dichalcogenides (TMDCs) exhibit prominent nonlinear optical properties. Direct epitaxial growth of large-area 1D/2D Te-TMDC vdW heterostructures is still rarely investigated. Herein, we demonstrate the controllable epitaxial growth of large-scale 1D/2D vertical Te-TMDC heterostructures via two-step vapor phase deposition method. Our experimental results have confirmed that the saturable absorption properties of as-prepared Te-TMDC heterostructures can be obviously enhanced. The first principle calculations and surface potential measurements demonstrate that effective interlayer charge transfer between Te NWs and TMDC nanosheets is beneficial for promoting the saturable absorption properties. Systematic investigation of vdW Te-TMDC heterostructures with nonlinear optical properties is vital for the next generation of nanophotonics and integrated photonics, which paves the way for the development of saturable absorbers and light modulators based on Te-TMDC vdW heterostructures.

Assembling a Photoactive 2D Puzzle: From Bulk Powder to Large-Area Films of Semiconducting Transition-Metal Dichalcogenide Nanosheets

ConspectusTwo-dimensional (2D) semiconducting materials are poised to revolutionize ultrathin, high-performance optoelectronic devices. In particular, transition-metal dichalcogenides (TMDs) are well-suited for applications requiring robust and stable materials such as electrocatalytic, photocatalytic, and photo-electrochemical devices. One of the most compelling assets of these materials is the ability to produce and process 2D TMDs in the nanosheet form using solution-based (SB) exfoliation methods. Compared to other methods, SB techniques are typically inexpensive, efficient, and more suitable for scale-up and industrial implementation. In acknowledgment of the importance of this area, much work has been done to develop various SB methods starting from the exfoliation of bulk crystalline TMD materials to the chemical modification of final devices consisting of thin films of semiconducting 2D TMD nanosheets. However, not all SB methods are equally compatible or interchangeable, and they result in very diverse material and device properties. Therefore, the aim of this Account is to provide an overview of the developed SB techniques that can serve as a guide for assembling high-performance thin films of 2D TMDs. We start by introducing the most popular methods for producing 2D TMDs using liquid-phase exfoliation (LPE), discussing their working mechanisms as well as their advantages and disadvantages. Notably we highlight a recently developed LPE technique using electro-intercalation that draws on the advantages of previously presented methods. Next, we discuss processing the as-produced 2D TMD nanosheets via SB separating techniques designed for size and morphology selection while also presenting the ongoing challenges in this area. We then examine SB methods for processing the selected 2D nanomaterial dispersions into semiconducting thin films. Various methods are compared and contrasted, and special attention is paid to a recently developed method that carefully deposits 2D TMD nanoflakes with preferential alignment and has been shown scalable to the meter-squared size range. Finally, we explore strategies for increasing the optoelectronic performance of the TMD films via device engineering and defect management. We scrutinize these post-treatments based on the final device application, which are explicitly discussed. In all of the discussed processes we present the most promising SB techniques giving critical analysis and insight from experience. While we provide our own “best practices”, we stress the use of adaptability and critical thinking when designing specifically tailored procedures. By providing examples of different uses and measured improvements in one comprehensive guide, we hope to simplify process-development and aid researchers in making their own unique photoactive 2D “puzzles”.

Electronic Structure of Colloidal 2H-MoS2 Mono and Bilayers Determined by Spectroelectrochemistry.

The electronic structure of mono and bilayers of colloidal 2H-MoS2 nanosheets synthesized by wet-chemistry using potential-modulated absorption spectroscopy (EMAS), differential pulse voltammetry, and electrochemical gating measurements is investigated. The energetic positions of the conduction and valence band edges of the direct and indirect bandgap are reported and observe strong bandgap renormalization effects, charge screening of the exciton, as well as intrinsic n-doping of the as-synthesized material. Two distinct transitions in the spectral regime associated with the C exciton are found, which overlap into a broad signal upon filling the conduction band. In contrast to oxidation, the reduction of the nanosheets is largely reversible, enabling potential applications for reductive electrocatalysis. This work demonstrates that EMAS is a highly sensitive tool for determining the electronic structure of thin films with a few nanometer thicknesses and that colloidal chemistry affords high-quality transition metal dichalcogenide nanosheets with an electronic structure comparable to that of exfoliated samples.

Surface Modification of Transition Metal Dichalcogenide Nanosheets for Intrinsically Self-Healing Hydrogels with Enhanced Mechanical Properties.

Nanocomposites with enhanced mechanical properties and efficient self-healing characteristics can change how the artificially engineered materials' life cycle is perceived. Improved adhesion of nanomaterials with the host matrix can drastically improve the structural properties and confer the material with repeatable bonding/debonding capabilities. In this work, exfoliated 2H-WS2 nanosheets are modified using an organic thiol to impart hydrogen bonding sites on the otherwise inert nanosheets by surface functionalization. These modified nanosheets are incorporated within the PVA hydrogel matrix and analyzed for their contribution to the composite's intrinsic self-healing and mechanical strength. The resulting hydrogel forms a highly flexible macrostructure with an impressive enhancement in mechanical properties and a very high autonomous healing efficiency of 89.92%. Interesting changes in the surface properties after functionalization show that such modification is highly suitable for water-based polymeric systems. Probing into the healing mechanism using advanced spectroscopic techniques reveals the formation of a stable cyclic structure on the surface of nanosheets, mainly responsible for theimproved healingresponse. This work opens an avenue toward the development of self-healing nanocomposites where chemically inert nanoparticles participate in the healing network rather than just mechanically reinforcing the matrix by slender adhesion.

Exciton recombination in few‐layer MoS2 nanosheets: Role of free carriers and defects

A current obstacle to the development of extremely flexible and high‐performance optoelectronic devices using transition metal dichalcogenide nanosheets is the incomplete understanding of the exciton and free carrier recombination in the presence of defects. Here, taking liquid‐phase exfoliated few‐layer MoS2 nanosheets as a model system, we demonstrate the exciton and free carrier recombination mechanism by employing pump energy and fluence‐dependent ultrafast transient absorption spectroscopy. We demonstrate that 3.10 eV pump excitation, much above the lowest energy A exciton of four to six layers of MoS2 nanosheets (~1.84 eV), generates excitons and free carriers. The excitons decay quickly within ~3 ps due to the defect capture via the Shockley–Read–Hall mechanism. In contrast, free carriers show slower recombination (~1000 ps), which is an order of magnitude larger than the exciton recombination time. We verified this idea by exciting the sample with 1.94–2.22 eV pump excitations that predominantly generate excitons decaying within ~3 ps. Our systematic studies in few‐layer MoS2 nanosheets reveal crucial information on the unexplored domain of excitons and free carriers recombination in the presence of defects for several optoelectronic applications.

Unraveling the joint toxicity of transition-metal dichalcogenides and per- and polyfluoroalkyl substances in aqueous mediums by experimentation, machine learning and molecular dynamics.

The environmental fate of transition-metal dichalcogenides (TMDCs) may be further complicated by interacting with existing pollutants, especially per- and polyfluoroalkyl substances (PFAS). However, due to their sheer volume, it is impossible to explore all possible interactions by simply utilizing experimental methods. Herein, we used two model TMDC nanosheets, molybdenum disulfide (MoS2) and tungsten disulfide (WS2), and seven PFAS to explore their interactions and subsequent impacts on model cell lines and zebrafish. Utilizing experimental methods and machine learning approaches, we showed that TMDCs-PFAS interactions can pose unique challenges due to their interaction-specific toxicity niches towards cell lines. Further in vivo experiments, together with molecular dynamics simulation, suggested that TMDCs-PFAS interactions in aqueous environments significantly increased their bioaccumulation in zebrafish towards different target organs, mostly due to the differences in loading PFAS. Such enhanced bioaccumulation increased the oxidative stress in zebrafish liver and intestine, as demonstrated by the increased reactive oxygen species (ROS) level and other enzyme activities, which eventually led to obvious histopathological alterations in the liver and intestine. Our study highlights the importance of exploring interactions between emerging and existing contaminants with state-of-art techniques in aqueous environments and its significance in safeguarding aquatic environment health.

Aspect ratio control of TaS2nanosheets: a methodology for room temperature formaldehyde gas sensing performance optimization

This work presents a gas sensor optimization strategy based on aspect ratio control of transition metal dichalcogenide nanosheets.