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![MBE growth of doped and alloyed 2D TMDs. a) MBE growth pathway of Nb doped WSe2 at 550 °C. At step 3, niobium sources and selenium sources are introduced to form NbSe2 around the outmost Nb‐WSe2 and smoothen the surface. Reproduced with permission.[¹⁰⁰] Copyright 2020, Springer Nature. b) ADF‐STEM image of mirror twin boundary (MTB) loop comprised of three MTBs, I, II, and III. Green circles indicate Nb dopants. The scale bar is 1 nm. Reproduced with permission.[¹⁰⁰] Copyright 2020, Springer Nature. c) Atomic structure of 4|4‐Se MTBs marked in (b) indicates the local Nb doping concentration inside the boundary. Reproduced with permission.[¹⁰⁰] Copyright 2020, Springer Nature. d) Simulated STM images and comparison to experimental images for Te vacancy in the negative charge states. Reproduced with permission.[¹⁰¹] Copyright 2019, Wiley‐VCH. e) Simulated STM images for V at Te site and V interstitial. Their corresponding atomic structures are shown below. Reproduced with permission.[¹⁰¹] Copyright 2019, Wiley‐VCH. f1–5) Atomic resolution STM images (15 × 15 nm²) of MoSe2, V0.26Mo0.74Se2, V0.55Mo0.45Se2, V0.78Mo0.22Se2, and VSe2 grown by MBE on graphite. Reproduced with permission.[⁶⁵] Copyright 2020, American Chemical Society. g1–5) Corresponding STS curves to each alloy shown in (f). (Set points: f1 1.6 V, 44 pA; f2, 1.2 V, 511 pA; f3, 0.5 V, 130 pA; f4, 0.3 V, 103 pA; and f5, −0.02 V, 200 pA.)Reproduced with permission.[⁶⁵] Copyright 2020, American Chemical Society. h) Evolution of (top) thermal stability and (bottom) electronic character of 2D VxMo1−x Se2 as a function of x. The narrow “stable” region in the top figure means that the thermally stable phase might exist when x < 0.05. In (bottom), for x ≤ 0.44, the 2D alloys are composed of semiconducting MoSe2 domains with metallic MTBs as well as homogeneous, metallic alloy domains. Reproduced with permission.[⁶⁵] Copyright 2020, American Chemical Society.](publication/349633556/figure/fig6/AS:11431281172806450@1688653834672/MBE-growth-of-doped-and-alloyed-2D-TMDs-a-MBE-growth-pathway-of-Nb-doped-WSe2-at-550C.png)
MBE growth of doped and alloyed 2D TMDs. a) MBE growth pathway of Nb doped WSe2 at 550 °C. At step 3, niobium sources and selenium sources are introduced to form NbSe2 around the outmost Nb‐WSe2 and smoothen the surface. Reproduced with permission.[¹⁰⁰] Copyright 2020, Springer Nature. b) ADF‐STEM image of mirror twin boundary (MTB) loop comprised of three MTBs, I, II, and III. Green circles indicate Nb dopants. The scale bar is 1 nm. Reproduced with permission.[¹⁰⁰] Copyright 2020, Springer Nature. c) Atomic structure of 4|4‐Se MTBs marked in (b) indicates the local Nb doping concentration inside the boundary. Reproduced with permission.[¹⁰⁰] Copyright 2020, Springer Nature. d) Simulated STM images and comparison to experimental images for Te vacancy in the negative charge states. Reproduced with permission.[¹⁰¹] Copyright 2019, Wiley‐VCH. e) Simulated STM images for V at Te site and V interstitial. Their corresponding atomic structures are shown below. Reproduced with permission.[¹⁰¹] Copyright 2019, Wiley‐VCH. f1–5) Atomic resolution STM images (15 × 15 nm²) of MoSe2, V0.26Mo0.74Se2, V0.55Mo0.45Se2, V0.78Mo0.22Se2, and VSe2 grown by MBE on graphite. Reproduced with permission.[⁶⁵] Copyright 2020, American Chemical Society. g1–5) Corresponding STS curves to each alloy shown in (f). (Set points: f1 1.6 V, 44 pA; f2, 1.2 V, 511 pA; f3, 0.5 V, 130 pA; f4, 0.3 V, 103 pA; and f5, −0.02 V, 200 pA.)Reproduced with permission.[⁶⁵] Copyright 2020, American Chemical Society. h) Evolution of (top) thermal stability and (bottom) electronic character of 2D VxMo1−x Se2 as a function of x. The narrow “stable” region in the top figure means that the thermally stable phase might exist when x < 0.05. In (bottom), for x ≤ 0.44, the 2D alloys are composed of semiconducting MoSe2 domains with metallic MTBs as well as homogeneous, metallic alloy domains. Reproduced with permission.[⁶⁵] Copyright 2020, American Chemical Society.
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Two‐dimensional (2D) transition metal dichalcogenides (TMDs) exhibit exciting properties and versatile material chemistry that are promising for device miniaturization, energy, quantum information science, and optoelectronics. Their outstanding structural stability permits the introduction of various foreign dopants that can modulate their optical...
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Citations
... A metal is sandwiched between two chalcogens. The interatomic force is covalent while interlayer is Van der Waals in nature [15]. These materials are characterized by having promising electronic and optical properties for application in photovoltaics [16,17]. ...
... Just like many other two-dimensional di-chalcogenides, 2D-MoTe2 is three atoms thick [15], a sheet Mo atoms sandwiched between two sheets of Te atoms, making a monolayer ( fig. 1). Their unique structural, electrical and optical properties make them different from their bulk ( fig. 1) counterpart and appealing for use in Photovoltaic. ...
With rapid progress in power conversion efficiencies, perovskite solar cells (PSCs) have shown great potential as next-generation low-cost, efficient solar cell device. Ultra-Thin pure and Br-doped MoTe2 monolayer materials are promising candidates for alternative electron transport material in perovskite solar cell application. The electronic, and optical properties of these materials were calculated using projector augmented plane wave (PAW) based on popular density-functional theory (DFT). These properties were calculated using Pardew-Burke-Ernzerhof generalized gradient approximation (PBE-GGA). The band structure for the considered materials have been determined using full relativistic spin-orbital coupling (SOC). Our results indicate that pure and Br-doped 2D-MoTe2 were n-type semiconductors and have direct band gap energies 1.01 and 1.2 eV respectively. The optical properties of the materials such as relative dielectric constant, transmission and reflectivity are presented. Using these properties, SCAPS-1D software is used to design a solar cells based on monolayer pure and Br-doped MoTe2 as electron transport layer (ETL). The maximum efficiencies of these cells are 22.76%, 22.99% with VOC of 0.7333 V, 0.7334 V and JSC of 37.221 mA/cm 2 , 37.229 mA/cm 2 were realized with the pure and Br-doped ETLs respectively. The performance of our solar cells is comparable to traditional Si-based solar cells. The results show how monolayer pure and Br-doped MoTe2 can serve as a suitable ETL materials for perovskite solar cell. .
... A metal is sandwiched between two chalcogens. The interatomic force is covalent while the interlayer is Van der Waals in nature [19]. These materials are characterized by having promising electronic and optical properties for application in photovoltaics [20,21]. ...
... Just like many other two-dimensional di-chalcogenides, 2D-MoTe2 is three atoms thick [19], a sheet of Mo atoms sandwiched between two sheets of Te atoms, making a monolayer (Fig. 1). Their unique structural, electrical and optical properties make them different from their bulk ( Fig. 1) counterparts and appealing for use in Photovoltaic. ...
With rapid progress in power conversion efficiencies, perovskite solar cells (PSCs) have shown great potential as next-generation low-cost, efficient solar cell devices. Ultra-thin pure and Br-doped MoTe2 monolayer materials are promising candidates for alternative electron transport material in perovskite solar cell applications. The electronic, and optical properties of these materials were calculated using projector augmented plane wave (PAW) based on popular density-functional theory (DFT). These properties were calculated using Pardew-Burke-Ernzerhof generalized gradient approximation (PBE-GGA). The band structure for the considered materials has been determined using full relativistic spin-orbital coupling (SOC). Our results indicate that pure and Br-doped 2D-MoTe2 were n-type semiconductors and had direct band gap energies of 1.01 and 1.21 eV respectively. The optical properties of the materials such as relative dielectric constant, transmission and reflectivity are presented. Using these properties, the 1-D solar cell capacitance simulator (SCAPS-1D) software was used to design solar cells based on monolayer pure and Br-doped MoTe2 as an electron transport layer (ETL). The maximum efficiencies of these cells are 13.121%, and 24.016% with VOC of 1.067 V and 1.186 V, JSC of 21.678 mA/cm 2 and 25.251 mA/cm 2 , and FF of 56.720% and 80.139% were realized with the pure and Br-doped ETLs respectively. The performance of our solar cells is comparable to traditional Si-based solar cells. The results show how monolayer pure and Br-doped MoTe2 can serve as a suitable ETL material for perovskite solar cells.
... Hence the suitable way to deal with this problem is the surface tailoring [30,31] and geometry modifications through foreign element doping [32][33][34] and defect engineering such as vacancy formation and stone wales defects [35,36] in order to enhance the gas sensing and capturing capability of monolayer h-BN system. Most of recent studies have already proven that, the metal atom decoration of 2D materials can significantly enhance their gas sensing properties [37,38], recent study carried out on Ti-Pd doped h-BN with varying doping configuration and sites for CO capturing and sensing indicate that Ti-Pd doped h-BN at B and N vacancies can hold CO molecule through chemisorption and adsorption techniques, respectively with satisfied energy ranges [39]. Very recently, an in-depth study was carried out for capturing of five different types of gases (i.e., H 2 , N 2 , CO, NO and CO 2 ) on various metal atom doped h-BN systems. ...
Titanium doped h-BN sheet is investigated for capture and dissociation of CO2 molecule with the adsorption of BeH2O, LiH2O, NaH2O and BeO compounds based on First-Principles and Molecular Dynamics (FPS-MD) calculations. BeH2O cluster helped the dissociation of CO2 into CO molecule by acquiring one O atom to its structure. Calculated adsorption energies indicate that the impurity substitution and adsorption process is exothermic and stable which can be adopted for experimental work. The interaction of CO2 with Ti atom is ionic in nature as O atom of CO2 molecule makes ionic bond with Ti atom for all configurations. Band structure plots were calculated, which indicated that Ti-doped h-BN band gap varied significantly when CO2 and other compounds were adsorbed on its surface thus proving the sensitivity of Ti-h-BN towards adsorbate systems. Obtained PDOS plots show significant hybridization peaks among the orbitals of CO2 molecules, adsorbate compounds and the Ti atom in deep valence bands; also keeping in view the adsorption energy range, it indicates the chemisorption behavior of adsorbates. Transition state search and activation energy barrier calculations were performed to explain the dissociation process of CO2 molecule. Through molecular dynamics calculations, obtained energy and temperature plots depicted smooth trend in their profile thus suggesting stabilized structures.
... Heterostructures based on 2D materials have recently been studied. Lin et al. 158 presented significant advancements in thin-film synthesis and processing methods that exhibit exceptional manipulation and dependability for substitutional doping of TMDCs thin film monolayers. WTe 2−x Se x− and V 1−x Mo x Se 2 159,160 structures are among the several 2D alloys that MBE can generate with exquisite controllability. ...
Two-dimensional transition metal dichalcogenides (2D-TMDCs) with various physical characteristics have attracted significant interest from the scientific and industrial worlds in the years following Moore's law. The p-n junction is one of the earliest electrical components to be utilized in electronics and optoelectronics, and modern research on 2D materials has renewed interest in it. In this regard, device preparation and application have evolved substantially in this decade. 2D TMDCs provide unprecedented flexibility in the construction of innovative p-n junction device designs, which is not achievable with traditional bulk semiconductors. It has been investigated using 2D TMDCs for various junctions, including homojunctions, heterojunctions, P-I-N junctions, and broken gap junctions. To achieve high-performance p-n junctions, several issues still need to be resolved, such as developing 2D TMDCs of superior quality, raising the rectification ratio and quantum efficiency, and successfully separating the photogenerated electron-hole pairs, among other things. This review comprehensively details the various 2D-based p-n junction geometries investigated with an emphasis on 2D junctions. We investigated the 2D p-n junctions utilized in current rectifiers and photodetectors. To make a comparison of various devices easier, important optoelectronic and electronic features are presented. We thoroughly assessed the review's prospects and challenges for this emerging field of study. This study will serve as a roadmap for more real-world photodetection technology applications.
... Thus, one possibility is that potassium has become doped within the layer. But theoretical calculations have suggested that substitutional doping by group 1 elements is energetically unfavorable at either the tungsten or sulfur sites 65,66 (although other work has suggested the opposite). 67 We also find no consistent evidence for additional bands in the Raman spectra that could be consistent with this, 41,64 with Raman also suggesting the flakes remain in the 2H phase. ...
Alkali-metal-based synthesis of transition metal dichalcogenide (TMD) monolayers is an established strategy for both ultralarge lateral growth and promoting the metastable 1T phase. However, whether this can also lead to modified optical properties is underexplored, with reported photoluminescence (PL) spectra from semiconducting systems showing little difference from more traditional syntheses. Here, we show that the growth of WS2 monolayers from a potassium-salt precursor can lead to a pronounced low-energy emission in the PL spectrum. This is seen 200–300 meV below the A exciton and can dominate the signal at room temperature. The emission is spatially heterogeneous, and its presence is attributed to defects in the layer due to sublinear intensity power dependence, a noticeable aging effect, and insensitivity to washing in water and acetone. Interestingly, statistical analysis links the band to an increase in the width of the A1g Raman band. The emission can be controlled by altering when hydrogen is introduced into the growth process. This work demonstrates intrinsic and intense defect-related emission at room temperature and establishes further opportunities for tuning TMD properties through alkali-metal precursors.
... Atomic-scale tailoring of materials is one of the most promising paths towards achieving new, both quantum and classical properties. Controllable defect engineering, i.e., introduction of vacancies or desired impurities, enables properties modifications and new functionalities in crystalline materials 1 . The opportunities for such controlled material engineering methods got a dramatic boost in the past two decades with the development of the methods for exfoliation of crystal into two-dimensional atomic layer 2 . ...
Two-dimensional materials offer a promising platform for the next generation of (opto-) electronic devices and other high technology applications. One of the most exciting characteristics of 2D crystals is the ability to tune their properties via controllable introduction of defects. However, the search space for such structures is enormous, and ab-initio computations prohibitively expensive. We propose a machine learning approach for rapid estimation of the properties of 2D material given the lattice structure and defect configuration. The method suggests a way to represent configuration of 2D materials with defects that allows a neural network to train quickly and accurately. We compare our methodology with the state-of-the-art approaches and demonstrate at least 3.7 times energy prediction error drop. Also, our approach is an order of magnitude more resource-efficient than its contenders both for the training and inference part.
... The most stable crystal phase is determined by the d-orbital electron numbers of the transition metal [35]. Most studies have investigated the impact of random doping in the 2H phase of trigonal prismatic TMDs [36]. Re-doped MoS2 nanosheets show a transformation from the 2H to 1T phase in both the Re and Mo coordinating structures, where the 1T ratios of both Mo and Re atoms were found to increase with the increasing Re-doping concentration, inducing the ferromagnetic ordering and stabilizing the metastable crystal phase [37]. ...
... The exploration of magnetically doped TMDs poses several challenges. First, the uniform and large-area TMD synthesis remains challenging due to the difficulty in controlling the flow of vaporized precursors and uncontrollable domain size [36]. Though room temperature ferromagnets were demonstrated, most of the magnetic TMDs show low Curie temperatures hampering the practical applications of these materials. ...
Transition metal dichalcogenides (TMDs) are two-dimensional (2D) materials with remarkable electrical, optical, and chemical properties. One promising strategy to tailor the properties of TMDs is to create alloys through a dopant-induced modification. Dopants can introduce additional states within the bandgap of TMDs, leading to changes in their optical, electronic, and magnetic properties. This paper overviews chemical vapor deposition (CVD) methods to introduce dopants into TMD monolayers, and discusses the advantages, limitations, and their impacts on the structural, electrical, optical, and magnetic properties of substitutionally doped TMDs. The dopants in TMDs modify the density and type of carriers in the material, thereby influencing the optical properties of the materials. The magnetic moment and circular dichroism in magnetic TMDs are also strongly affected by doping, which enhances the magnetic signal in the material. Finally, we highlight the different doping-induced magnetic properties of TMDs, including superexchange-induced ferromagnetism and valley Zeeman shift. Overall, this review paper provides a comprehensive summary of magnetic TMDs synthesized via CVD, which can guide future research on doped TMDs for various applications, such as spintronics, optoelectronics, and magnetic memory devices.
... To provide insightful guidance on the development of 2D-TMD-based devices, we present in Table 1 a list of promising 2D-TMD magnets and heterostructures. While most of the 2D-TMD DMSs are synthesized using chemical vapor deposition (CVD), some of their heterostructures are grown by molecular beam epitaxy (MBE) or a combination of both techniques [76]. CVD typically produces 2D films with uniformity, low porosity, high purity, and stability, but generates toxic gases during the reaction. ...
... CVD typically produces 2D films with uniformity, low porosity, high purity, and stability, but generates toxic gases during the reaction. MBE enables in-situ preparation of atomically clean substrates with specific surface reconstructions, facilitating the growth of highly epitaxial 2D films, but it can result in more defects during film growth [74][75][76]. It is essential to advance these techniques for growing defect-free or defect-controllable 2D-TMD DMSs and heterostructures. ...
The capacity to manipulate magnetization in two-dimensional dilute magnetic semiconductors (2D-DMSs) using light, specifically in magnetically doped transition metal dichalcogenide (TMD) monolayers (M-doped TX2, where M = V, Fe, Cr; T = W, Mo; X = S, Se, Te), may lead to innovative applications in spintronics, spin-caloritronics, valleytronics, and quantum computation. This Perspective paper explores the mediation of magnetization by light under ambient conditions in 2D-TMD DMSs and heterostructures. By combining magneto-LC resonance (MLCR) experiments with density functional theory (DFT) calculations, we show that the magnetization can be enhanced using light in V-doped TMD monolayers (e.g., V-WS2, V-WSe2, V-MoS2). This phenomenon is attributed to excess holes in the conduction and valence bands, as well as carriers trapped in magnetic doping states, which together mediate the magnetization of the semiconducting layer. In 2D-TMD heterostructures such as VSe2/WS2 and VSe2/MoS2, we demonstrate the significance of proximity, charge-transfer, and confinement effects in amplifying light-mediated magnetism. This effect is attributed to photon absorption at the TMD layer (e.g., WS2, MoS2) that generates electron-hole pairs mediating the magnetization of the heterostructure. These findings will encourage further research in the field of 2D magnetism and establish a novel direction for designing 2D-TMDs and heterostructures with optically tunable magnetic functionalities, paving the way for next-generation magneto-optic nanodevices.
... As an example, where only 6-8 eV per atom is required to desorb a chalcogen atom, 20-30 eV per atom is required to desorb a transition metal atom. 75 Therefore, doping during the growth is preferred for metal substitution, which works more efficiently when done in a metal-deficient or chalcogen-rich environment. 74 A. p-type doping MoS 2 , which is the most researched 2D material after graphene, shows n-type character in its pristine form due to the presence of sulfur vacancies, hydrogen interstitials, or H-S adatoms coming from the growth environment. ...
To support the ever-growing demand for faster, energy-efficient computation, more aggressive scaling of the transistor is required. Two-dimensional (2D) transition metal dichalcogenides (TMDs), with their ultra-thin body, excellent electrostatic gate control, and absence of surface dangling bonds, allow for extreme scaling of the channel region without compromising the mobility. New device geometries, such as stacked nanosheets with multiple parallel channels for carrier flow, can facilitate higher drive currents to enable ultra-fast switches, and TMDs are an ideal candidate for that type of next generation front-end-of-line field effect transistor (FET). TMDs are also promising for monolithic 3D (M3D) integrated back-end-of-line FETs due to their ability to be grown at low temperature and with less regard to lattice matching through van der Waals (vdW) epitaxy. To achieve TMD FETs with superior performance, two important challenges must be addressed: (1) complementary n- and p-type FETs with small and reliable threshold voltages are required for the reduction of dynamic and static power consumption per logic operation, and (2) contact resistance must be reduced significantly. We present here the underlying strengths and weaknesses of the wide variety of methods under investigation to provide scalable, stable, and controllable doping. It is our Perspective that of all the available doping methods, substitutional doping offers the ultimate solution for TMD-based transistors.
... Recently, Lin et. al. 20 reported excellent controllability for substitutional doping of the foreign atoms in 2D TMDs through low energy ion implantation techniques such as site-selective laser-assisted chemical vapor doping 21 . Furthermore, a very recent experimental work demonstrates a controlled doping strategy for TMDs based on a dislocation climb mechanism 22 . ...
The state-of-the-art defect engineering techniques have paved the way to realize novel quantum phases out of pristine materials. Here, through density-functional calculations and model studies, we show that the chain-doped monolayer transition metal dichalcogenides (TMDs), where M atoms on a single the zigzag chains are replaced by a higher-valence transition-metal element M$^\prime$ (MX$_2$/M$^\prime$), exhibit one-dimensional (1D) bands. These 1D bands, occurring in the fundamental gap of the pristine material, are dispersive along the doped chain but are strongly confined along the lateral direction. This confinement occurs as the bare potential of the dopant chain formed by the positively charged M$^\prime$ ions resembles the potential well of a uniformly charged wire. These bands could show novel 1D physics, including a new type of Tomonaga-Luttinger liquid behavior, multi-orbital Mott insulator physics, and an unusual optical absorption, due to the simultaneous presence of the spin-orbit coupling, strong correlation, multiple orbitals, Rashba spin splitting, and broken symmetry. For the half-filled 1D bands, we find, quite surprisingly, a broadening of the 1D bands due to correlation, as opposed to the expected band narrowing. This is interpreted to be due to multiple orbitals forming the single Hubbard band at different points of the Brillouin zone. Furthermore, due to the presence of an intrinsic electric field along the lateral direction, the 1D bands are Rashba spin-split and provide a new mechanism for tuning the valley dependent optical transitions.
