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Atomistic mechanisms of seeding promoter-controlled growth of molybdenum disulphide
摘要： Seeding promoters facilitate the nucleation and growth of transition metal dichalcogenides in chemical vapor deposition (CVD). However, sophisticated roles of seeding promoter remain unclear. Here, adopting triangular-shaped crystal violet (CV) consisting of nonpolar and polar parts as the seeding promoter, we study the role of seeding promoter for the growth of molybdenum disulfide (MoS2). We systematically control the geometrical configuration of CV on SiO2/Si substrate by changing the solvent polarity and find that it strongly affects the growth of monolayer or multilayer MoS2 domains via CVD. Monolayer MoS2 domains were predominantly grown on randomly lying-down CV configurations on SiO2/Si substrate, whereas multilayer MoS2 domains are synthesized at concentrated polar parts in CV micelle on the substrate. Density functional theory calculations reveal that the initial nucleation step for the MoS2 growth is the adsorption of S on CV and the most favourable S adsorption site is the polar part in CV. Furthermore, it is found that the polar CV part mediates the CV adsorption to SiO2 and additionally strengthened in the lying-down CV configuration. Enhancing the thermal stability as well as hindering the re-aggregation of CV at high temperature, the lying down CV configuration allows the predominant growth of monolayer MoS2.
关键词： seeding promoter,molybdenum disulphide,chemical vapour deposition,transition metal dichalcogenides
更新于2025-09-23 15:19:57
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Giant Stark effect in coupled quantum wells: Analytical model
摘要： Coupled quantum wells have been proposed as candidates for highly polarizable structures due to their near-degenerate and dipole-coupled electronic states. Hence, many interesting applications in linear and nonlinear optics can be envisioned. We analyze this proposal considering a simple structure with a delta-function barrier separating the wells. While very substantial Stark shifts are certainly predicted for this geometry, perturbative estimates based on polarizabilities (and hyperpolarizabilities) fail beyond a critical ?eld strength that depends inversely on the barrier. Hence, a giant Stark effect due to near-degenerate states is invariably limited by a small critical ?eld. Our analytical (hyper) polarizability expressions are applied to ?nd quantitative Stark shifts for GaAs quantum wells and transition-metal dichalcogenide bilayers. The predicted Stark shifts and critical ?elds agree with the ?eld dependence observed in a range of available experiments.
关键词： Stark effect,hyperpolarizability,GaAs,transition-metal dichalcogenide bilayers,polarizability,coupled quantum wells
更新于2025-09-23 15:19:57
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In situ atomic level studies of thermally controlled interlayer stacking shifts in 2D transition metal dichalcogenide bilayers
摘要： We show interlayer stacking shifts occur in transition metal dichalcogenides (TMD) bilayers due to the strain introduced during sample heating, and attributed to rippling of one layer relative to the other. The atomic structure of the interlayer stacking is studied using annular dark field scanning transmission electron microscopy with an in situ heating holder. Before heating, bilayers show uniform interlayer stacking of AA9 and AB. When heated, contrast change is seen and associated with interlayer stacking changes at the atomic scale due to ripples. When cooled down to room temperature, these contrast features disappear, confirming it is a reversible process that is not related to defects or vacancies. Because the bottom layer is attached to the in situ heating chip made from Si3N4 and the top layer is in contact with the underlying TMD layer with weak van der Waals interaction, the two layers experience different forces during thermal expansion.
关键词： transition metal dichalcogenides,thermal expansion,scanning transmission electron microscopy,interlayer stacking,2D materials
更新于2025-09-23 15:19:57
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Intrinsic-strain-induced curling of free-standing two-dimensional Janus MoSSe quantum dots
摘要： Motivated by the fascinating properties of both two-dimensional transition metal dichalcogenide quantum dots (TMD QDs) and Janus TMD monolayers, we theoretically explore the equilibrium structures of free-standing Janus MoSSe QDs in which atomic asymmetry of chalcogen is introduced. Two distinct types of spontaneous curling are observed by molecular dynamics simulations, and the curling behavior depends on the size of QD. The bowl-like (tube-like) curling occurs in relatively small (large) MoSSe QDs with di?erent shapes (hexagon and triangle) and edge types (zigzag and armchair). The transition between these two curling types occurs at the sizes of around 10 nm and 13 nm for hexagonal and triangular shapes, respectively. By applying equivalent mis?t strains into two adjacent sublayers, ?nite element analysis reproduces similar curling behavior. This con?rms the relaxation of intrinsic strain in Janus structure acting as the predominant driving force of spontaneous curling. In addition, the curvatures of Janus TMD QDs increase from MoSSe to MoSeTe to MoSTe, indicating the positive correlation between the curling and mis?t.
关键词： Intrinsic strain,Janus transition metal dichalcogenides,Molecular dynamics,Quantum dot,Finite element method
更新于2025-09-23 15:19:57
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Overview of Synthetic Methods to Prepare Plasmonic Transition Metal Nitride Nanoparticles
摘要： The search for new plasmonic materials that are low-cost, chemically and thermally stable, and exhibit low optical losses has garnered significant attention among researchers. Recently, metal nitrides have emerged as promising alternatives to conventional, noble metal based plasmonic materials such as Ag and Au. Many of the initial studies on metal nitrides have focused on computational prediction of the material plasmonic properties. In recent years, several synthetic methods have been developed, enabling empirical analysis. This review highlights synthetic techniques for the preparation of plasmonic metal nitride nanoparticles which are predominantly free-standing using solid-state and solid-gas phase reactions, non-thermal and arc plasma methods, and laser ablation. The physical properties of the nanoparticles such as shape, size, crystallinity, and optical response obtained with such synthetic methods are also summarized.
关键词： Plasmonics,nanoparticles,next-generation materials,transition metal nitrides,metamaterials
更新于2025-09-23 15:19:57
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Electrically controlled dielectric band gap engineering in a two-dimensional semiconductor
摘要： The emergent class of atomically thin two-dimensional (2D) materials has opened up completely new opportunities for manipulating electronic quantum states at the nanoscale. Here we explore the concept of dielectric band gap engineering, i.e., the controlled manipulation of the band gap of a semiconductor via its dielectric environment. Using first-principles calculations based on the GW self-energy approximation we show that the band gap of a two-dimensional (2D) semiconductor, such as the transition metal dichalcogenides, can be tuned over several hundreds of meV by varying the doping concentration in a nearby graphene sheet. Importantly, these significant band gap renormalizations are achieved via nonlocal Coulomb interactions and do not affect the structural or electronic integrity of the 2D semiconductor. We investigate various heterostructure designs, and show that, depending on the size of the intrinsic dielectric function of the 2D semiconductor, the band gap can be tuned by up to 1 eV for graphene carrier concentrations reachable by electrostatic doping. Our work provides opportunities for electrically controllable band gap engineering in 2D semiconductors.
关键词： GW self-energy approximation,transition metal dichalcogenides,graphene,two-dimensional semiconductor,dielectric band gap engineering
更新于2025-09-23 15:19:57
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Nanoscale Interfaces of Janus Monolayers of Transition Metal Dichalcogenides for 2D Photovoltaic and Piezoelectric Applications
摘要： Using first-principles calculations, we demonstrate a combination of two emergent fields, type-II van der Waal heterostructures and Janus structures, for the purpose of optimizing the harvesting of solar and nanoelectromechanical energy. The most stable stacking order in these nanoscale heterobilayers comprising of Janus monolayers of transition metal dichalcogenides has been ascertained based on the interlayer binding energies. The binding energies in WSeTe/WSTe and MoSeTe/WSTe heterobilayers are found to be -27.93 and -25.67 meV/?2 at an equilibrium interlayer layer distance of 3.25 ? and 3.32 ? respectively, indicating the exothermicity in the process of heterobilayer formation and hence, its experimental feasibility. The mechanical and dynamical stabilities have also been confirmed for these heterobilayers using the Born Huang stability criteria and phonon dispersion calculations. Our results unveil the mechanism underlying the electronic, piezoelectric, photocatalytic properties and carrier mobility in these Janus heterobilayers. Power conversion efficiency in the 2D ultrathin excitonic solar cells constituted by some of the heterobilayers studied in this work, has been found to lie in the range of 15-20%. Moreover, a very high carrier mobility (>200 cm2/V.s) together with a large visible light absorption coefficient (α ~ 105 cm-1) has been observed in these hetero-bilayers. The piezoelectric coefficients in these ultrathin heterobilayers (d33 = 13.91 pm/V) is found to reach close to the values obtained in multilayer/bulk structures built from Janus monolayers of Mo-based dichalcogenides. Our findings highlight the promising applications of these heterobilayers in ultrathin excitonic solar cells, nanoelectronics and nanopiezotronics.
关键词： van der Waals heterostructures,transition metal dichalcogenides,photovoltaic applications,Janus monolayers,piezoelectricity,carrier mobility
更新于2025-09-23 15:19:57
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Monolithic Contact Engineering to Boost Optoelectronic Performances of 2D Semiconductor Photovoltaic Heterojunctions
摘要： In optoelectronic devices based on two-dimensional (2D) semiconductor heterojunctions, the efficient charge transport of photogenerated carriers across the interface is a critical factor to determine the device performances. Here, we report an unexplored approach to boost the optoelectronic device performances of the WSe2-MoS2 p-n heterojunctions via the monolithic-oxidation-induced doping and resultant modulation of the interface band alignment. In the proposed device, the atomically thin WOx layer, which is directly formed by layer-by-layer oxidation of WSe2, is used as a charge transport layer for promoting hole extraction. The use of the ultrathin oxide layer significantly enhanced the photoresponsivity of the WSe2-MoS2 p-n junction devices, and the power conversion efficiency increased from 0.7 to 5.0%, maintaining the response time. The enhanced characteristics can be understood by the formation of the low Schottky barrier and favorable interface band alignment, as confirmed by band alignment analyses and first-principle calculations. Our work suggests a new route to achieve interface contact engineering in the heterostructures toward realizing high-performance 2D optoelectronics.
关键词： Contact engineering,Transition metal dichalcogenides,Heterostructures,Photovoltaics,2D semiconductors,Optoelectronics
更新于2025-09-23 15:19:57
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Performance enhancement of CIGS thin-film solar cells with a functional-window NiO thin layer
摘要： Cu(In1-χGaχ)Se2 (CIGS) films have been considered as promising materials for solar cell applications owing to high absorption coefficient, bandgap grading, flexibility, and high conversion efficiency. In particular, the bandgap grading has been widely researched as a back surface field effect to reduce the carrier recombination. Recently, the front surface field has been researched by the application of a transition metal oxide (TMO) to increase the power conversion efficiency (PCE). Among them, NiO is an outstanding TMO layer because of its wide bandgap (~3.7 eV), stable cubic structure, the low electron affinity of 1.33~1.85 eV and p-type characteristics. Consequently, the application of the NiO layer has been researched on the CIGS solar cells as an effective electron blocking barrier, which is to suppress the carrier recombination. Even though much research has proceeded on the versatile properties of the NiO, there is rarely research to apply the NiO layer on the CIGS solar cells yet. In this study, we introduced the application of NiO layer deposition on the CIGS solar cell to improve the PCE. The NiO layer (20nm) was deposited on the CIGS solar cell using the E-beam evaporator system at room temperature. We investigated the effect of the application of the p-NiO layer on the CIGS solar cells, comparing the efficiencies and dark J-V curves. These results are in good agreement with time-resolved photoluminescence measurements on the carrier lifetime. The PCE of the device with the p-NiO layer was measured as 16.35 % and the PCE of the device without the p-NiO layer was measured as 15.81 %. After the application of the p-NiO layer, we gained the improvement with 0.54 % of the PCE.
关键词： CIGS,transition metal oxide,solar cell,NiO,thin film,functional layer
更新于2025-09-23 15:19:57
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Delayed Charge Recombination by Opena??Shell Organics: Its Application in Achieving Superb Photodetectors with Broadband (400a??1160 nm) Ultrahigh Sensitivity and Stability
摘要： Monolayer transition-metal dichalcogenides have inspired worldwide efforts in optoelectronic devices but real applications are hindered with their reduced optical absorption due to their atomically ultrathin signature. In this study, by utilizing their biradical nature such as excellent absorption coefficient, broad bandwidth from the ultraviolet to near-infrared region, and small triplet–singlet energy gap, a series of helicene 5,14-diaryldiindeno[2,1-f:1′,2′-j]picene (DDP) derivatives (1ab, 1ac, and 1bb) are integrated with monolayer MoS2 for extraordinary photodetector performance and outstanding stability. Via comprehensive time-resolved studies, the interfacial charge-transfer process from the DDPs to the MoS2 layer is evidenced by the stabilized exciton property of the organics (1ac)/MoS2 heterostructure. Significantly, the 1ac/MoS2 photodetector exhibits an ultrahigh photoresponsivity of 5 × 107 A W?1 and a fast response speed of 45 ms due to the highly efficient photoexcited carrier separation and the matched type-II energy band alignment. The biradical 1ac/MoS2 hybrid photodetector shows no sign of degradation after one-month operation. The results pave a new avenue for biradical based high-performance and super-broadband optoelectronic devices.
关键词： photodetectors,hybrid structures,MoS2,biradical organic molecules,transition metal dichalcogenides
更新于2025-09-23 15:19:57