Two-dimensional Transition Metal Chalcogenides Research Articles

An emerging quaternary semiconductor nanoribbon with gate-tunable anisotropic conductance

Two-dimensional noble transition metal chalcogenide (NTMC) semiconductors represent compelling building blocks for fabricating flexible electronic and optoelectronic devices. While binary and ternary compounds have been reported, the existence of quaternary NTMCs with a greater elemental degree of freedom remains largely unexplored. This study presents the pioneering experimental realization of a novel semiconducting quaternary NTMC material, AuPdNaS2, synthesized directly on Au foils through chemical vapor deposition. The ribbon-shaped morphology of the AuPdNaS2 crystal can be finely tuned to a thickness as low as 9.2 nm. Scanning transmission electron microscopy reveals the atomic arrangement, showcasing robust anisotropic features; thus, AuPdNaS2 exhibits distinct anisotropic phonon vibrations and electrical properties. The field-effect transistor constructed from AuPdNaS2 crystal demonstrates a pronounced anisotropic conductance (σmax/σmin = 3.20) under gate voltage control. This investigation significantly expands the repertoire of NTMC materials and underscores the potential applications of AuPdNaS2 in nano-electronic devices.

Single-atom catalysts supported on two-dimensional tetragonal transition metal chalcogenides for hydrogen and oxygen evolution

Single-atom catalysts (SACs) offer maximum metal atom utilization and high catalytic performance. Transition metal atoms on two-dimensional (2D) materials are effective for improving electrocatalytic performance. However, few studies exist on SACs supported on 2D tetragonal transition metal chalcogenides (TMX) for OER and HER. We report a detailed theoretical study using DFT calculations on SACs supported on TMX monolayers, denoted as TMA@TMBX. Our findings demonstrate that seven TMA@TMBX electrocatalysts surpass IrO2 (ηOER= 0.56 V), with four TMA@TMBX exhibiting a reduced OER overpotential compared to RuO2 (ηOER= 0.42 V). Additionally, four TMA@TMBX exhibit higher HER performance than Pt (111) (ηHER= 0.10 V). We ultimately identified three SACs with high bifunctional HER/OER activity: Co@NiSe, Rh@NiTe, and Co@NiS. This study on TMA@TMBX provides insights for enhancing the HER and OER activities of SACs supported on 2D materials, which could have significant implications in clean and renewable energy.

Unveiling the ligand-mediated phase engineering mechanism in two-dimensional transition metal chalcogenides through coordination geometry control

Spectroscopic investigation of tungsten dichalcogenide nanosheets is reported, where the differentiated metal–ligand coordination geometry influenced by the choice of appropriate ligands is a pivotal factor for the phase-selective formation.

Theoretical study of CDW phases for bulk NbX2 (X = S and Se).

In most two-dimensional transition metal chalcogenides, the superconducting phase coexists with the charge density wave (CDW) phase. There exists at least one case, i.e. bulk 2H-NbS2, that does not conform to this picture. Scientists have shown great interest in trying to experimentally find the CDW phase of bulk NbS2 since 1975. Is there any theoretically more stable thermodynamic state than its higher-temperature metal phase, especially in the case of charge injection? Theoretically more stable CDW bulk configurations (TC for 2H-NbS2 and TTs for 2H-NbSe2) with partial pseudo energy gaps were predicted through the harmonic phonon softening theory and first-principles calculations. The ratios of larger to smaller pseudo gaps around K-H segment in the Brillouin zone for CDW phases are basically equal to those of superconductivity phases for bulk 2H-NbX2 (X = S and Se). The CDW phase should coexist with its superconductor state below the critical temperature rather than the metal phase for bulk 2H-NbS2. The presence of CDW phase should be more easily observed experimentally when the injected charge reaches 0.5e/Nb18S36 for bulk 2H-NbS2. Our calculations of density of state (DOS) indicated that, during Nb atoms contracting to form the CDW phases with symmetry breaking in the in-plane direction, dominant conductive carriers are always of p-type for bulk 2H-NbS2 while the alternation of carrier type from p-type to n-type occurs for bulk 2H-NbSe2. The Fermi level continuously drops and then the M-L segment of the out-of-plane energy band emerges from the Fermi surface, which corresponds to the reversal of p-n type sign. Lifshitz transition of pocket-vanishing types occurs in the out-of-plane direction without symmetry breaking during the geometrical structural phase transition for bulk 2H-NbSe2. Our calculations have theoretically addressed the long-standing coexistence issue of CDW and superconducting phases.

Effects of strain and thickness on the mechanical, electronic, and optical properties of Cu2Te.

Two-dimensional transition-metal chalcogenides (TMCs) have attracted considerable attention because of their exceptional photoelectric properties, finding applications in diverse fields such as photovoltaics, lithium-ion batteries, catalysis, and energy conversion and storage. Recently, experimentally fabricated monolayers of semiconducting Cu2Te have emerged as intriguing materials with outstanding thermal and photoelectric characteristics. In this study, we employ first-principles calculations to investigate the mechanical, electronic, and optical properties of monolayer Cu2Te exhibiting both λ and ζ structures, considering the effects of thickness and strain. The calculations reveal the robust mechanical stability of λ-Cu2Te and ζ-Cu2Te under varying thickness and strain conditions. By applying -5% to +5% strain, the band gaps can be modulated, with ζ-Cu2Te exhibiting an indirect-to-direct transition at a biaxial strain of +5%. In addition, a semiconductor-to-metal transition is observed for both ζ-Cu2Te and λ-Cu2Te with increasing thickness. The absorption spectra of λ-Cu2Te and ζ-Cu2Te exhibit a redshift with an increase in the number of layers. These computational insights into Cu2Te provide valuable information for potential applications in nano-electromechanical systems, optoelectronics, and photocatalytic devices and may guide subsequent experimental research efforts.

(Invited) Advanced Atomic Layer Deposition Cycle Schemes for Large-Area Synthesis of 2D Transition Metal Dichalcogenides

2D materials have been the focus of intense research in the last decade due to their unique physical properties. This presentation will highlight our recent progress on the large-area synthesis of two-dimensional transition metal chalcogenides for nanoelectronics using advanced atomic layer deposition cycle schemes. First, how we can use advanced cycle schemes to deposit wafer-scale polycrystalline MoS2 thin films at very low temperatures down to 100 °C. We have identified the critical role of hydrogen during the plasma step in controlling the composition and properties of molybdenum sulfide films. By increasing the H2/H2S ratio or adding an extra hydrogen plasma step to our ALD process, we are able to deposit pure polycrystalline MoS2 films at temperatures as low as 100 °C. To the best of our knowledge, this represents the lowest temperature for crystalline MoS2 films prepared by any chemical gas-phase method.[1]ALD-grown 2D films tend to exhibit a high density of out-of-plane 3D structures in addition to 2D horizontal layers. While the out-of-plane 3D structures are ideal for catalysis applications, the presence of such 3D structures can hinder charge transport, which hampers device applications. In this presentation I will show how we used mechanistic insight obtained by HRTEM to tune the shape and density of the 3D structures during plasma-enhanced ALD using advanced atomic layer deposition schems. The obtained morphology control was further confirmed by electrical measurements.[2]Earlier [3] we have shown that ALD is an excellent technique to make MoxW1-xS2 alloys with precise control over the alloy composition. Here, I will focus on how (plasma-enhanced) atomic layer deposition can aid in synthesizing doped 2DTMCs with precise control over the doping concentration by using elaborate ALD dosing schemes.[1] M. Mattinen et al., Chem. Mater. (2022), 34, 5104[2] S. Balasubramanyam, et al. ACS Appl. Mater. Interfaces (2020), 12, 3873[3] J. J. P. M. Schulpen et al. 2D Mater. (2022), 9, 025016

Two-Dimensional Tetragonal Transition Metal Chalcogenides for High Performance Oxygen Evolution and Reduction: A DFT Study.

The pursuit of high-performance bifunctional catalysts for oxygen evolution/reduction (OER/ORR) has gained significant attention in the field of electrochemical water splitting and fuel cells. In this study, we employed density functional theory (DFT) calculations to investigate a series of 2D tetragonal TMX (TM=transition metal, X=S, Se, Te) monolayers as potential bifunctional electrocatalysts for OER/ORR. To evaluate the overall performance of OER electrocatalysts, we introduced a descriptor, Gmax. The Gmax values obtained for tetragonal CdS, CdSe, FeSe, NiSe, and NiTe monolayers were all below 1.0 V, indicative of their superior catalytic activity and selectivity. Moreover, NiSe displayed remarkable ORR capability with an overpotential (ηORR ) of 0.53 V. Based on the bifunctional index (BI), the catalytic activity ranking for the bifunctional catalysts is as follows: NiSe>NiTe>FeSe>CdS>CdSe>NiS>TiSe>ZnTe. These findings provide an insightful understanding of the electrocatalytic properties of 2D tetragonal TMX monolayers for OER/ORR, opening avenues for the future development of efficient bifunctional electrocatalysts based on 2D tetragonal transition metal chalcogenides.

Research on the mechanism of interactions between Li/Na/K atoms and electrode materials

As the demand for high-capacity battery materials continues to grow, the exploration of the interaction mechanisms between Li/Na/K atoms and electrode materials has gained tremendous attention. In this study, we introduce a descriptor (ɛɑ) aimed at efficiently identifying high-performance electrode materials, specifically from two-dimensional transition metal chalcogenides and C and N compounds (MXenes). Our density functional theory calculations disclose a robust linear relationship between this descriptor and the adsorption energy (Ead), represented as Ead = ɛɑ + b. The fitting parameters, ɛɑ and b, are individually linked to the inherent properties of the substrate and adsorbate. Explicitly, the descriptor ɛɑ represents the capacity of the electrode material to accommodate an extra electron, while the intercept b is determined by the ionization energy (EIP) of alkali atoms and the coupling energy (Ecp) between the cation to the negatively charged substrate. This finding serves as a practical guide for designing high-capacity battery materials and paves the way for future advancements in this field.

Temperature dependent charge carrier dynamics in 2D ternary Cu2MoS4 nanoflakes: An effect of electron-phonon coupling.

Two-dimensional transition metal chalcogenides (2D TMCs) like MoS2, WS2 etc., have established significant dominance in the field of nanoscience and nanotechnology, owing to their unique properties like strong light-matter interaction, high carrier mobility, large photo-responsivity etc. Despite the widespread utilization of these binary TMCs, their potential in the advancement of the optoelectronic research is limited due to the constraints in band tuning and charge carrier lifetime. To overcome these limitations, ternary transition metal chalcogenides have emerged as promising alternatives. Although, the optical properties of these materials have never been explored properly. Herein, we have investigated one such promising member of this group, Cu2MoS4 (CMS) using both steady state and time-resolved spectroscopic techniques. The material exhibits a broad range of visible light absorption, peaking at 576nm. Photoluminescence spectroscopy confirmed the presence of both band gap emission and trap state-mediated emissions. Transient absorption spectroscopy unraveled the excited state charge carrier dynamics of CMS in sub-ps timescale, upon irradiation of visible light. We found significant influence of the trap mediated recombination, while Auger process being dominant at high charge density. We extended our study in a wide temperature range (5-300K), which reveals the impact of electron-phonon coupling strength on the band gap and charge carrier dynamics of this material. This detailed study would draw more attention toward the unexplored optical properties of ternary 2D chalcogenides and will open new avenues for the construction of 2D material-based optical devices.

Theoretical evidence of self-intercalated 2D materials for battery and electrocatalytic applications

Covalently bonded two-dimensional (2D) self-intercalated transition metal chalcogenides (i.e., ic-2Ds) have been recently fabricated experimentally, and their properties are highly tunable by stoichiometry and composition. Inspired by this progress, we focus on the applications of ic-2Ds in the field of electrochemistry and systematically investigate their performance in lithium-ion batteries (LIBs) and electrocatalytic hydrogen evolution reactions (HER). By means of density functional theory calculations, seven 3d -metal ic-2Ds are confirmed to be thermodynamically, mechanically, and thermally stable. The metallicity and abundant active sites endow these ic-2Ds with the potential as excellent electrode materials and HER catalysts. Among them, Ti7S12 and V7S12 exhibit the potential as anode materials for LIBs, showing low Li diffusion energy barriers, suitable open-circuit voltages, and ultrahigh capacity of 745.6 and 723.9 mA hg-1, respectively; Cr7S12 and Co7S12 show promises for HER with moderate hydrogen adsorption strengths. This theoretical study provides a new avenue for the application of newly reported ic-2Ds in various electrochemical energy conversion and storage applications.

Multiband Monochromatic Upconversion Emissions of Lanthanide Codoped Monolayer MoS2 Nanosheets for Lighting Applications

Upconversion materials have attracted much attention because of their broad application prospects in biomedicine and energy. Although various methods have been tried in nanoparticles and nanocrystals, it is still a challenge to realize monochromatic upconversion luminescence (UCL) in traditional lanthanide-doped materials. Two-dimensional transition metal chalcogenides (2D-TMDs) are a class of excellent luminescent semiconductors, offering a promising platform due to their chemical accessibility and physical sensitivity. However, multi-lanthanide doping, typically boosting the upconversion efficiency, has not been accomplished in monolayer TMD nanosheets. In this work, an optimized liquid precursor-assisted technique is designed to synthesize monolayer MoS2 nanosheets embedded with Er/Yb and Er/Ho by surmounting the precipitation of Ln3+-doped precursors, which is confirmed by structural characterization. The monolayer MoS2 can split the 4f configuration remarkably to produce diverse energy levels due to its strong Coulomb binding and spin–orbit coupling, as well as the unique asymmetric crystal field along the [001] direction. Hence, multiband monochromatic UCL from violet to near-infrared ranges was obtained on these codoped MoS2 nanosheets. This work provides an effective way to tune the luminescence performance and wavelength of 2D-TMD nanosheets as well as a strategy for the design of UCL nanomaterials for light applications as nanophotonic devices.

Growth of wafer-scale chromium sulphide and selenide semiconductor films

Two-dimensional (2D) transition metal chalcogenides have attracted enormous attention due to their stunning properties and great prospects for applications. Most of the reported 2D materials have layered structure, and non-layered transition metal chalcogenides are rare. Particularly, chromium chalcogenides are highly complexed in terms of structural phases. Researches on their representative chalcogenides, Cr2S3 and Cr2Se3, are insufficient and most of them focus on individual crystal grains. In this study, large-scale Cr2S3 and Cr2Se3 films with controllable thickness are successfully grown, and their crystalline qualities are confirmed by multiple characterizations. Moreover, the thickness-dependent Raman vibrations are investigated systematically, presenting slight redshift with increasing thickness. The fundamental physical properties of grown Cr2S3 and Cr2Se3 films, including optical bandgap, activation energy and electrical properties, are measured with different thicknesses. The 1.9 nm thick Cr2S3 and Cr2Se3 films show narrow optical bandgap of 0.732 and 0.672 eV, respectively. The electrical properties of Cr2S3 films demonstrate p-type semiconductor behaviours, while the Cr2Se3 films exhibit no gate response. This work can provide a feasible method for growing large-scale Cr2S3 and Cr2Se3 films, and reveal fundamental information of their physical properties, which is helpful for future applications.

Direct Spectroscopic Observation of Cross-Plane Heat Transfer in a Two-Dimensional Van der Waals Heterostructure

Two-dimensional (2D) transition metal chalcogenides (TMDs) have drawn significant attention in recent years due to their extraordinary optical and electronic properties. As heat transfer plays an important role in device performance, various methods such as optothermal Raman spectroscopy and time-domain thermoreflectance have been developed to measure the thermal conductivity and interfacial thermal conductance in 2D van der Waals (vdW) heterostructures. Here, we employ the vibrational-pump-visible-probe (VPVP) spectroscopy to directly visualize the heat transfer process in a heterostructure of multilayer h-BN and monolayer WS2. Following an impulsive vibrational excitation of h-BN in the mid-infrared, we probe the heat transfer from h-BN through WS2 and finally to the substrate from the subpicosecond to the submicrosecond timescale. The interfacial thermal conductance of the h-BN/WS2 and WS2/SiO2 interfaces is obtained by corroborating the experiments with heat transfer calculations based on the Fourier’s law of heat conduction. Our study demonstrates an alternative, time-resolved optical method to measure cross-plane heat dissipation and opens up a new pathway to investigate the interlayer electron–phonon and phonon–phonon interactions in vdW heterostructures.

Room-temperature antiferromagnetic CrSe monolayer with tunable metal–insulator transition in ferroelectric heterostructures

Recently, there has been a rapidly growing interest in two-dimensional (2D) transition metal chalcogenide monolayers (MLs) due to their unique magnetic and electronic properties. By using an evolutionary algorithm and first-principles calculations, we report the discovery of a previously unexplored, chemically, energetically, and thermodynamically stable 2D antiferromagnetic (AFM) CrSe ML with a Néel temperature higher than room temperature. Remarkably, we predict an electric field-controllable metal–insulator transition in a van der Waals heterostructure comprised of CrSe ML and ferroelectric Sc2CO2. This tunable transition in the CrSe/Sc2CO2 heterostructure is attributed to the change in the band alignment between CrSe and Sc2CO2 caused by the ferroelectric polarization reversal in Sc2CO2. Our findings suggest that 2D AFM CrSe ML has important potential applications in AFM spintronics, particularly in the gate voltage conducting channel.

External field regulation strategies for exciton dynamics in 2D TMDs

Two-dimensional (2D) transition metal chalcogenides (TMDs) are regarded as promising materials for micro-optoelectronic devices and next-generation logic devices due to their novel optoelectronic properties, such as strong excitonic effects, tunable direct bandgap from visible to near-infrared regions, valley pseudospin degree of freedom, and so on. Recently, triggered by the growing demand to optimize the performance of TMDs devices, external field regulation engineering has attracted great attention. The goal of this operation is to exploit the external fields to control exciton dynamics in 2D TMDs, including exciton formation and relaxation, and to finally achieve high-performance 2D TMDs devices. Although the regulation strategies of exciton dynamics in 2D TMDs have been well explored, the underlying mechanisms of different regulation strategies need to be further understood due to the complex many-body interactions in exciton dynamics. Here, we first give a brief summary of the fundamental processes of exciton dynamics in 2D TMDs and then summarize the main field-regulation strategies. Particular emphasis is placed on discussing the underlying mechanisms of how different field-regulation strategies control varied fundamental processes. A deep understanding of field regulation provides direct guidelines for the integrated design of 2D TMDs devices in the future.

Structure modulation of two-dimensional transition metal chalcogenides: recent advances in methodology, mechanism and applications.

Together with the development of two-dimensional (2D) materials, transition metal dichalcogenides (TMDs) have become one of the most popular series of model materials for fundamental sciences and practical applications. Due to the ever-growing requirements of customization and multi-function, dozens of modulated structures have been introduced in TMDs. In this review, we present a systematic and comprehensive overview of the structure modulation of TMDs, including point, linear and out-of-plane structures, following and updating the conventional classification for silicon and related bulk semiconductors. In particular, we focus on the structural characteristics of modulated TMD structures and analyse the corresponding root causes. We also summarize the recent progress in modulating methods, mechanisms, properties and applications based on modulated TMD structures. Finally, we demonstrate challenges and prospects in the structure modulation of TMDs and forecast potential directions about what and how breakthroughs can be achieved.

Prediction of band gap of transition metal sulfide with Janus structure by deep learning atomic feature representation method

With the development of artificial intelligence, machine learning (ML) is more and more widely used in material computing. To apply ML to the prediction of material properties, the first thing to do is to obtain effective material feature representation. In this paper, an atomic feature representation method is used to study a low-dimensional, densely distributed atomic eigenvector, which is applied to the band gap prediction in material design. According to the types and numbers of atoms in the chemical formula of material, the Transformer Encoder is used as a model structure, and a large number of material chemical formula data are trained to extract the features of the training elements. Through the clustering analysis of the atomic feature vectors of the main group elements, it is found that the element features can be used to distinguish the element categories. The Principal Component Analysis of the atomic eigenvector of the main group element shows that the projection of the atomic eigenvector on the first principal component reflects the outermost electron number corresponding to the element. It illustrates the effectiveness of atomic eigenvector extracted by using the transformer model. Subsequently, the atomic feature representation method is used to represent the material characteristics. Three ML methods named Random Forest (RF), Kernel Ridge Regression (KRR) and Support Vector Regression (SVR) are used to predict the band gap of the two-dimensional transition metal chalcogenide compound MXY (M represents transition metal, X and Y refer to the different chalcogenide elements) with Janus structure. The hyperparameters of ML model are determined by searching for parameters. To obtain stable results, the ML model is tested by 5-fold cross-validation. The results obtained from the three ML models show that the average absolute error of the prediction using atomic feature vectors based on deep learning is smaller than that obtained from the traditional Magpie method and the Atom2Vec method. For the atomic eigenvector method proposed in this paper, the prediction accuracy of the KRR model is better than that of the results obtained from the Magpie method and Atom2Vec method. It shows that the atomic feature vector proposed in this paper has a certain correlation between the features, and is a low-dimensional and densely distributed feature vector. Visual analysis and numerical experiments of material property prediction show that the atomic feature representation method based on deep learning extraction proposed in this paper can effectively characterize the material features and can be applied to the tasks of material band gap prediction.

Electronic and magnetic structure of ultrathin Co9Se8 nanosheets and Co9Se8 bulk from density functional theory calculations

Two-dimensional transition-metal chalcogenides are one of the most interesting new classes of 2D materials. 2D cobalt selenide nanomaterials are being actively pursued and investigated as well, and recently, the first large-scale synthesis of half-unit-cell-thick Co9Se8 nanosheets has been reported. In the present study, using density functional theory calculations and employing the advanced hybrid HSE06 exchange-correlation functional, the electronic and magnetic structure of Co9Se8 nanosheets is investigated. To allow a comparison with bulk, the electronic and magnetic properties of Co9Se8 bulk are investigated as well. The bulk phase is found to be a ferrimagnetic semiconductor. Reducing the dimensions of Co9Se8 bulk to form a half-unit-cell-thick Co9Se8 nanosheet strongly alters the electronic and magnetic structure of the material. The nanosheet is predicted to have a different type of ferrimagnetic ordering and to be a metal with semimetallic features. Analysis of the X–M segment of the nanosheet's band structure, which mainly determines the electronic transport properties of the material, shows that within this segment, the main band below the Fermi level consists of only spin-up states (Se 4p), while the main band above the Fermi level consists of only spin-down states (Se 4p hybridized with Co 3d). This combination points to possibilities of selective conductivity of either spin-up or spin-down electrons and indicates that ultrathin Co9Se8 nanosheets are a most promising candidate for nanoelectronic and spintronic applications.

Nonlinear optical properties and broadband ultrafast photonics application of 2D-zirconium tritelluride (ZrTe3)

Two-dimensional (2D) transition metal chalcogenides (TMCs) have lately attracted broad interest in advanced photonics field due to their tunable bandgap, high broadband absorption, and excellent nonlinear optical (NLO) performances. Among other TMCs, group-IV transition metal trichalcogenides (TMTs) are rarely investigated for the NLO applications. Zirconium tritelluride (ZrTe3) is a kind of group-IV TMTs that shows metallic behavior among TMTs materials. While several electrical properties of ZrTe3 have been studied recently, the research community is longing to explore NLO features of ZrTe3. Herein, by using open aperture Z-scan method, the NLO properties of ZrTe3-nanosheets are investigated. The admirable NLO characteristics of ZrTe3 are realized from the obtained highest nonlinear absorption coefficient value of −82.1 × 103 in 1 µm and −13.05 × 103 cm/GW in 1.5 µm. Moreover, broadband fiber optics ZrTe3-based saturable absorbers (SAs) are prepared for the first time by depositing 2D-ZrTe3 nanosheets on a side-polished fiber. Following integration of these ZrTe3-SAs into three distinct rare earth-doped fiber laser cavities, stable mode-locking pulses with pulse widths of 323 ps (1 µm), 751 fs (1.5 µm), and 1.2 ps (2 µm) are obtained, respectively. These findings indicate that the ZrTe3 can facilitate the exploration of 2D materials in nonlinear optics and ultrafast photonics applications.

Controllable Potassium Iodide-Assisted Preparation of Two-dimensional SnS2 for Hydrogen Evolution Reaction

The controllable preparation of Two-dimensional transition metal chalcogenides (TMDCs) is very important. However, the uncontrollable growth of SnS2 by chemical vapor deposition (CVD) and the unsatisfactory performance of hydrogen evolution reaction (HER) based on SnS2 have hindered its applications. Herein, we reported the direct synthesis of high-quality 1T-SnS2 with various morphologies via potassium iodide-assisted CVD. On the basis of CVD technology, We have developed process technology to grow different shapes of SnS2 from dot line to fishbone controlled by growth conditions. The growth mechanism of SnS2 was studied, and their HER performance with different morphologies of SnS2 was investigated. The growth trend of 2D SnS2 provides a reference for the controllable preparation of TMDCs materials. These results demonstrate that TMDCs can adjust the performance of HER through shape control.