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![Large area exfoliation of monolayer TMDs. (a) Au-exfoliation process flow. (b) Histograms for MoS2 flake areas exfoliated using tape-exfoliation versus Au-exfoliation. (c) PL map of an ultra-large flake exfoliated using Au-exfoliation. (a)–(c) Reprinted with permission from [40]. Copyright 2016 Wiley.](publication/311529993/figure/fig1/AS:11431281211424106@1702394925297/Large-area-exfoliation-of-monolayer-TMDs-a-Au-exfoliation-process-flow-b-Histograms.jpg)
Large area exfoliation of monolayer TMDs. (a) Au-exfoliation process flow. (b) Histograms for MoS2 flake areas exfoliated using tape-exfoliation versus Au-exfoliation. (c) PL map of an ultra-large flake exfoliated using Au-exfoliation. (a)–(c) Reprinted with permission from [40]. Copyright 2016 Wiley.
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The rise of two-dimensional (2D) materials research took place following the isolation of graphene in 2004. These new 2D materials include transition metal dichalcogenides, mono-elemental 2D sheets, and several carbide- and nitride-based materials. The number of publications related to these emerging materials has been drastically increasing over t...
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Electrical metal contacts to two-dimensional (2D) semiconducting transition metal dichalcogenides (TMDCs) are found to be the key bottleneck to the realization of high device performance, due to strong Fermi level pinning and high contact resistances (Rc). Until now, Fermi level pinning of monolayer TMDCs has been reported only theoretically, altho...
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... The lack of standardized characterization protocols further hinders the comparison of results across studies. Moreover, 2D materials are highly sensitive to defects, the underlying substrate, and their interfaces with other materials, making consistent characterization even more difficult [27]. ...
Characterizing defects in 2D materials, such as cracks in chemical vapor deposited (CVD)-grown hexagonal boron nitride (hBN), is essential for evaluating material quality and reliability. Traditional characterization methods are often time-consuming and subjective and can be hindered by the limited optical contrast of hBN. To address this, we utilized a YOLOv8n deep learning model for automated crack detection in transferred CVD-grown hBN films, using MATLAB’s Image Labeler and Supervisely for meticulous annotation and training. The model demonstrates promising crack-detection capabilities, accurately identifying cracks of varying sizes and complexities, with loss curve analysis revealing progressive learning. However, a trade-off between precision and recall highlights the need for further refinement, particularly in distinguishing fine cracks from multilayer hBN regions. This study demonstrates the potential of ML-based approaches to streamline 2D material characterization and accelerate their integration into advanced devices.
... Each type of discharge has specific characteristics that influence the formation of different carbon allotropes such as: monolayer and multilayer graphene, carbon nanotubes, and other carbon nanostructures. Depending on the synthesis method, each of the carbon nanostructures can have a wide range of properties, which can be utilized for applications in multifunctional polymeric compounds [17,18], optical and electronic devices [19,20], energy storage devices [21,22], solar cells [23], chemical filters [24], and many other products. ...
In this study, carbon nanostructures were synthesized utilizing a warm plasma jet at atmospheric pressure in a continuous and catalyst-free process. The procedure and apparatus were designed and constructed in our laboratory. Plasma was generated with 600 W of electrical energy, using a high-voltage, high-frequency alternating current power source. The working gas utilized was a propane/butane mixture, with a concentration ratio of 60:40, respectively. A production rate of 300 mg min⁻¹ of powdered material was achieved, with a particle size between 20 and 100 nm. The product was characterized by Fourier transform infrared spectroscopy, thermogravimetric analysis, Raman spectroscopy, x-ray diffraction, and transmission electron microscopy. Results show the formation of multilayer carbon nanostructures with a low content of functional groups; the obtained material presented structural defects and amorphous carbon. This work demonstrates that, with adequate control, warm plasma jet discharges can be employed for the synthesis of carbon nanostructures. The process is scalable and can be utilized for hydrocarbon reforming and hydrogen production. However, further studies are needed to improve the quality of the nanostructures and process efficiency. The synthesized material can potentially be used in gas adsorption or in the manufacture of polymeric nanocomposites with enhanced thermal, electrical, and mechanical properties.
... The origin of these characteristics is due to their honeycomb structure with a unique symmetry and higher surface-to-volume ratio. One of the intriguing features of TMDs, which makes them exceptional, is their tunable bandgap, which varies as the number of layers changes from indirect at multilayer to direct at single layer [2,3], making them potential candidates for a wide range of electronics, optoelectronics, energy storage, and catalytic applications [4][5][6]. Therefore, the investigation of the thickness-dependent properties of emerging TMDs have been receiving increased attention in recent years. ...
Two-dimensional (2D) layered transition-metal based tellurides (chalcogens) are known to harness their surface atoms’ characteristics to enhance topographical activities for energy conversion, storage, and magnetic applications. The gradual stacking of each sheet alters the surface atoms’ subtle features such as lattice expansion, leading to several phenomena and rendering tunable properties. Here, we have evaluated thickness-dependent mechanical properties (nanoscale mechanics, tribology, potential surface distributions, interfacial interaction) of 2D CoTe2 sheets and magnetic behavior using surface probe techniques. The experimental observations are further supported and explained with theoretical investigations: density functional theory and molecular dynamics. The variation in properties observed in theoretical investigations unleashes the crucial role of crystal planes of the CoTe2. The presented results are beneficial in expanding the use of the 2D telluride family in flexible electronics, piezo sensors, tribo-generators, and next-generation memory devices.
... Several synthesis methods, including mechanical exfoliation [3], powder vaporization [6,7], pulsed laser deposition [8], chemical vapor deposition (CVD), and metal-organic chemical vapor deposition (MOCVD) [9][10][11][12] are being deployed in a bid to improve both the quality and scalability of the grown TMDs. Associated with the materials synthesis is the need for an efficient characterization technique to determine the various features of the samples, ranging from the basic crystal qualities to the determination of the properties and potential applications of the materials [13,14]. ...
Materials characterization remains a labor-intensive process, with a large amount of expert time required to post-process and analyze micrographs. As a result, machine learning has become an essential tool in materials science, including for materials characterization. In this study, we perform an in-depth analysis of the prediction of crystal coverage in WSe 2 thin film atomic force microscopy (AFM) height maps with supervised regression and segmentation models. Regression models were trained from scratch and through transfer learning from a ResNet pretrained on ImageNet and MicroNet to predict monolayer crystal coverage. Models trained from scratch outperformed those using features extracted from pretrained models, but fine-tuning yielded the best performance, with an impressive 0.99 𝑅 2 value on a diverse set of held-out test micrographs. Notably, features extracted from MicroNet showed significantly better performance than those from ImageNet, but fine-tuning on ImageNet demonstrated the reverse. As the problem is natively a segmentation task, the
segmentation models excelled in determining crystal coverage on image patches. However, when applied to full images rather than patches, the performance of segmentation models degraded considerably, while the regressors did not, suggesting that regression models may be more robust to scale and dimension changes compared to segmentation models. Our results demonstrate the efficacy of computer vision models for automating sample characterization in 2D materials while providing important practical considerations for their use in the development of chalcogenide thin films.
... The advent of two-dimensional (2D) layered materials beyond graphene has initiated a new field of research [1][2][3]. In the family of 2D layered structures, transition metal dichalcogenides (TMDs) have attracted considerable attention from academia and regarding potential applications [4][5][6][7][8][9] because of a number of remarkable properties [10][11][12]. ...
Raman spectroscopy is a widely used technique to characterize nanomaterials because of its convenience, non-destructiveness, and sensitivity to materials change. The primary purpose of this work is to determine via Raman spectroscopy the average thickness of MoS 2 thin films synthesized by direct liquid injection pulsed-pressure chemical vapor deposition (DLI-PP-CVD). Such samples are constituted of nanoflakes (with a lateral size of typically 50 nm, i.e., well below the laser spot size), with possibly a distribution of thicknesses and twist angles between stacked layers. As an essential preliminary, we first reassess the applicability of different Raman criteria to determine the thicknesses (or layer number, N ) of MoS 2 flakes from measurements performed on reference samples, namely well-characterized mechanically exfoliated or standard chemical vapor deposition MoS 2 large flakes deposited on 90 ± 6 nm SiO 2 on Si substrates. Then, we discuss the applicability of the same criteria for significantly different DLI-PP-CVD MoS 2 samples with average thicknesses ranging from sub-monolayer up to three layers. Finally, an original procedure based on the measurement of the intensity of the layer breathing modes is proposed to evaluate the surface coverage for each N (i.e., the ratio between the surface covered by exactly N layers and the total surface) in DLI-PP-CVD MoS 2 samples.
... Over the past decade, the discovery and successful exfoliation of a single layer of graphene [1,2], revealing its unique characteristics, has generated great interest in the study of 2D materials [3]. A multitude of monolayer materials, both theoretically * Author to whom any correspondence should be addressed. ...
Auxetic materials are in high demand for advanced applications due to their relatively rare negative Poisson’s ratio in two-dimensional materials. This study investigates the structural, mechanical, electronic, optical and photocatalytic properties of the AsBiTe3 monolayer using first-principles calculations. Through analysis of phonon dispersion curves, ab-initio molecular dynamics simulations, and Born conditions, we have confirmed the thermal, dynamic, and mechanical stability of the AsBiTe3 monolayer. The study of the mechanical properties of this material revealed significant anisotropy and a bidirectional in-plane negative Poisson’s ratio (NPR). In addition, electronic band structures calculated, with and without spin-orbit coupling (SOC) using the HSE functional, indicate that this monolayer exhibits the characteristics of an indirect-gap semiconductor around 1.17 and 1.32 eV, respectively. Notably, by assessing the optical properties of AsBiTe3 monolayer, it has been found that this monolayer has a strong light-harvesting capability with an absorption coefficient higher than 10-5 cm-1 in the visible region. Fascinatingly, under a biaxial 1% and 4% tensile and -2% compressive strain, the band edge of the AsBiTe3 monolayer extends across the redox potential of water at pH = 0, 7 and 14, respectively. This suggests that this monolayer holds promise as a potential material for catalytic water splitting. These results should inspire further experimental and theoretical research, aimed at fully exploring the potential applications of this new class of 2D materials.
... Despite recent breakthroughs in enhancing these procedures, which aim to cut costs and manufacture larger crystals, it is obvious that these technologies are still costly and have scaling limitations [560][561][562][563]. While MXenes show promise in a variety of fields, much work is necessary to make them widely available. ...
MXenes belong to a set of 2-dimensional (2D) materials composed of transition metals, carbides, nitrides, and carbonitrides demonstrated unique properties in several fields including catalysis and energy storage. This review provides a comprehensive overview of the recent trends in MXene-based catalysts for hydrogen evolution reactions (HER) and their potential applications in energy storage devices. MXenes are widely sought-after as HER catalysts because of their distinctive properties including large surface area, variable surface chemistry, and high electrical conductivity. Extensive research in their synthesis, characterization, and performance reveals their superior catalytic activity, stability, and affordability compared to conventional catalysts. They have also shown great promise for use in energy storage devices notably supercapacitors and batteries. This review paper examines various synthesis techniques and emphasizes how various factors affect catalysis with MXenes for HER. The 2D structure of MXenes enables effective charge storage and transfer, with excellent conductivity and numerous active sites for species adsorption. In the MXenes domain, a crucial gap exists lack of a thorough review on recent advancements, specifically focusing on electrocatalysts for HER and energy storage in batteries. This concise narrative systematically addresses current progress, challenges, proposing solutions, briefly exploring synthesis methods, and delving into applications including prospective HER catalysts and strategies for enhanced activity and energy storage, especially in sodium, lithium, and zinc ion batteries.)
... However, the development of an adequate photolithography process for 2D materials is still in its early stages [30]. This circumstance limits the widespread use of the CVD technique in the fabrication of electrical devices based on MTMD material [31,32]. Therefore, the controllable synthesis of MTMD materials with a reduced deposition temperature has become a hot topic. ...
Metallic transition-metal dichalcogenides are emerging as promising electrode materials for applications such as 2D electronic devices owing to their good electrical conductivity. In this study, a high-performance humidity sensor based on NbTe2 electrode material and an indium-doped SnO2 thin film sensing layer was fabricated using a pulsed laser deposition system. The morphology, structural, elemental compositions, and electrical properties of the as-deposited samples were characterized. Additionally, the humidity sensing response of the fabricated sensor with In-doped SnO2 (8:92 wt%) sensing film was evaluated in a wide range of relative humidity at room temperature. The results demonstrated that the humidity sensor based on In-doped SnO2 exhibited a high sensitivity of 103.1 Ω/%RH, fast response and recovery times, a low hysteresis value, good linearity, and repeatability. In addition, the sensor had good long-term stability, with a variation in impedance of less than 3%. The results indicated that the humidity sensor could be suitable for practical humidity sensing applications.
... Beside these, other top-down method that can be used for exfoliating 2D materials are laser based exfoliation and ball milling assisted exfoliation. However, ball milling produces non-uniform flake size of 2D crystals [63,64] and laser based exfoliation is known to create various defects during the exfoliation process mainly from the heat generated in the exfoliation process [65,66]. Hence even though there is no toxicological effect in these 2D materials synthesis process, the quality and size of flake is the major issue that has inhibited in using these techniques. ...
Miniaturization of the devices in terms of size and the necessity of high speed device performance have created opportunities as well as challenges in the material research community. Nanomaterials like 0D and 2D materials are one of such material choices that can help realize the nanosize and ultrafast devices. However, the growth process of these materials, especially emerging 2D materials, needs to be reviewed in terms of human, animal and environmental toxicity along with the economic cost for synthesizing material. Moreover, the green and sustainable alternatives for minimizing or eliminating the toxicity should also be considered for the commercial scale nanomaterials synthesis and device fabrication. This topic will thus highlight the currently developed 2D materials, their growth process, application prospective, toxicity effect and their possible sustainable alternatives.
... This research has revealed novel physical properties in 2D materials, and has driven the search for new 2D semiconducting materials, leading to breakthroughs in nanoelectronics [15][16][17], sensing [18,19], energy storage [20,21], energy conversion [22,23], photonics [24,25], optoelectronics [14], magnetoresistance [26], and valleytronics [27,28]. However, like any other materials, defects are inevitable in 2D materials, and their presence can significantly affect their properties [29][30][31][32]. Structural defects, such as vacancies, dislocations, and grain boundaries, can alter their electronic and mechanical properties [33][34][35][36]. ...
Two-dimensional (2D) transition metal dichalcogenide (TMD) materials have versatile electronic and optical properties. TMD nanoribbons exhibit interesting properties due to reduced dimensionality, quantum confinement, and edge states, which make them suitable for various electronic and optoelectronic applications. In a previous work conducted by our group, we demonstrated that the edge bands evolved with bending can tune the optical properties for various widths of TMD nanoribbons. Defects are commonly present in 2D TMD materials, and can dramatically change the material properties. In this following work, we investigate the interaction between the edge and the defect states in tungsten disulfide (WS2) nanoribbons with lines of W- or S-atom vacancies defects under different bending conditions, using density functional theory (DFT). To gain understanding about the limits of density functional approximations, we compare results on band gaps and energies of defect states with quasiparticle GW. We reveal interesting semiconductor-metal phase transitions, suggesting potential applications in nanoelectronics or molecular electronics. We also calculate the optical absorption of the bent and defective nanoribbons with the many-body GW-BSE (Bethe-Salpeter equation) approach, revealing a tunable optical spectrum and diverse exciton states in the defective WS2 nanoribbons.
