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[NanoScience and Technology] Silicene (Prediction, Synthesis, Application) || Germanene: Silicene’s Twin Sister
摘要： Soon after the discovery of graphene, the first two-dimensional material, many other two-dimensional materials have been developed. Due to their s2 p2 type of electronic structure the elements of the ‘carbon’ column of the periodic system i.e. silicon, germanium and tin have received a lot of attention as potential two-dimensional materials. The silicon, germanium and tin analogues of graphene are coined silicene, germanene and tinene or stanene, respectively, and share many properties with graphene. There are, however, also a few distinct differences with graphene. Here we will give a brief update on the current status of germanene. We briefly review the various routes to synthesize germanene and elaborate on its structural and electronic properties as well as its potential for application in future electronic devices.
关键词： silicene,two-dimensional materials,electronic properties,synthesis,germanene
更新于2025-09-23 15:21:01
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Complementary doping of van der Waals materials through controlled intercalation for monolithically integrated electronics
摘要： Doping control has been a key challenge for electronic applications of van der Waals materials. Here, we demonstrate complementary doping of black phosphorus using controlled ionic intercalation to achieve monolithic building elements. We characterize the anisotropic electrical transport as a function of ion concentrations and report a widely tunable resistivity up to three orders of magnitude with characteristic concentration dependence corresponding to phase transitions during intercalation. As a further step, we develop both p-type and n-type field effect transistors as well as electrical diodes with high device stability and performance. In addition, enhanced charge mobility from 380 to 820 cm2/(V·s) with the intercalation process is observed and explained as the suppressed neutral impurity scattering based on our ab initio calculations. Our study provides a unique approach to atomically control the electrical properties of van der Waals materials, and may open up new opportunities in developing advanced electronics and physics platforms.
关键词： nanoelectronics,two-dimensional (2D) materials and heterostructures,tunable properties,diode,black phosphorus,FET
更新于2025-09-23 15:19:57
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Structural Evolutions of Vertically-Aligned Two-Dimensional MoS <sub/>2</sub> Layers Revealed by <i>In Situ</i> Heating Transmission Electron Microscopy
摘要： Benefited from a large density of layer edges exposed on the surface, vertically-aligned two-dimensional (2D) molybdenum disulfide (MoS2) layers have recently harvested excellent performances in the field of electrochemical catalysis and chemical sensing. With their increasing versatility for high-temperature demanding applications, it is vital to identify their thermally-driven structural and chemical stability as well as clarify its underlying principle. Despite various ex situ and in situ characterizations on horizontally-aligned 2D MoS2 layers, the direct in situ heating of vertically-aligned 2D MoS2 layers and the real-time observation of their near-atomic scale dynamics have never been approached, leaving their thermal stability poorly understood. Moreover, the geometrical advantage of the surface-exposed vertically-aligned 2D MoS2 layers is anticipated to unveil the structural dynamics of interlayer van der Waals (vdW) gaps and its correlation with thermal energy, unattainable with 2D MoS2 layers in any other geometry. Herein, we report a comprehensive in situ heating TEM study on cleanly transferred vertically-aligned 2D MoS2 layers up to 1000 °C. Several striking phenomena were newly observed in the course of heating: (1) formation and propagation of voids between the domains of vertical 2D MoS2 layers with distinct grain orientations starting at ~875 °C, (2) subsequent decompositions of the 2D MoS2 layers accompanying a formation of Mo nanoparticles at ~950 °C, much lower than the melting temperature of their bulk counterpart, and (3) initiation of decomposition from the surface-exposed 2D layer vertical edge sites, congruently supported by molecular dynamics (MD) simulation. These new findings will offer critical insights into better understanding the thermodynamic principle that governs the structural stability of general vdW 2D crystals as well as providing useful technological guidance for materials design and optimization in their potential high-temperature applications.
关键词： van der Waals gaps,in situ heating,structural evolution,MoS2,two-dimensional,vertically-aligned,transmission electron microscopy,thermal stability,molecular dynamics simulation
更新于2025-09-23 15:19:57
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Light-Enhanced Ion Migration in Two-Dimensional Perovskite Single Crystals Revealed in Carbon Nanotubes/Two-Dimensional Perovskite Heterostructure and Its Photomemory Application
摘要： Two-dimensional (2D) hybrid perovskite sandwiched between two long-chain organic layers is an emerging class of low-cost semiconductor materials with unique optical properties and improved moisture stability. Unlike conventional semiconductors, ion migration in perovskite is a unique phenomenon possibly responsible for long carrier lifetime, current?voltage hysteresis, and low-frequency giant dielectric response. While there are many studies of ion migration in bulk hybrid perovskite, not much is known for its 2D counterparts, especially for ion migration induced by light excitation. Here, we construct an exfoliated 2D perovskite/carbon nanotube (CNT) heterostructure field effect transistor (FET), not only to demonstrate its potential in photomemory applications, but also to study the light induced ion migration mechanisms. We show that the FET I?V characteristic curve can be regulated by light and shows two opposite trends under different CNT oxygen doping conditions. Our temperature-dependent study indicates that the change in the I?V curve is probably caused by ion redistribution in the 2D hybrid perovskite. The first principle calculation shows the reduction of the migration barrier of I vacancy under light excitation. The device simulation shows that the increase of 2D hybrid perovskite dielectric constant (enabled by the increased ion migration) can change the I?V curve in the trends observed experimentally. Finally, the so synthesized FET shows the multilevel photomemory function. Our work shows that not only we could understand the unique ion migration behavior in 2D hybrid perovskite, it might also be used for many future memory function related applications not realizable in traditional semiconductors.
关键词： photomemory,carbon nanotube,ion migration,Two-dimensional perovskite,heterostructure
更新于2025-09-23 15:19:57
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One-step H2S reactive sputtering for 2D MoS2/Si heterojunction photodetector
摘要： A technique for directly growing two-dimensional (2D) materials onto conventional semiconductor substrates, enabling high-throughput and large-area capability, is required to realise competitive 2D transition metal dichalcogenide devices. A reactive sputtering method based on H2S gas molecules and sequential in-situ post-annealing treatment in the same chamber was proposed to compensate for the relatively deficient sulfur atoms in the sputtering of MoS2 and then applied to a 2D MoS2/p-Si heterojunction photodevice. X-ray photoelectron, Raman, and UV-visible spectroscopy analysis of the as-deposited Ar/H2S MoS2 film were performed, indicating that the stoichiometry and quality of the as-deposited MoS2 can be further improved compared with the Ar-only MoS2 sputtering method. For example, Ar/H2S MoS2 photodiode has lower defect densities than that of Ar MoS2. We also determined that the factors affecting photodetector performance can be optimised in the 8–12 nm deposited thickness range.
关键词： H2S gas,two-dimensional layered MoS2,reactive sputtering,heterojunction photodiode
更新于2025-09-23 15:19:57
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Discovery of Novel Two-Dimensional Photovoltaic Materials Accelerated by Machine Learning
摘要： Searching for novel, high-performance, two-dimensional photovoltaic (2DPV) materials is an important pursuit for solar cell applications. In this work, an efficient method based on the machine learning algorithm combined with high-throughput screening is developed. Twenty-six 2DPV candidates are successfully ruled out from 187093 experimentally identified inorganic crystal structures, whose conversion efficiencies are predicted by density functional theory calculations. Our results indicate that Sb2Se2Te, Sb2Te3, and Bi2Se3 exhibit conversion efficiencies that are much higher than those of others, which make them promising 2DPV candidates for further applications. The superior photovoltaic performance is then analyzed, and the hidden structure-related relationships with photovoltaic properties are established, thus providing important information for the further examination of 2DPV materials. Given the rapid development of the database of materials, this approach not only provides an efficient way of searching for novel 2DPV materials but also can be applied to exploration of a broad range of functional materials.
关键词： high-throughput screening,machine learning,solar cell applications,density functional theory,two-dimensional photovoltaic materials
更新于2025-09-23 15:19:57
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First-principle study of g-AlxGa1-xN alloys: planar and buckled structures
摘要： The fundamental properties of g-AlxGa1-xN alloys with planar and buckled structures are investigated based on the first-principles. The results show that the band gaps of g-AlxGa1-xN alloys can be tuned, making them promising candidate materials for future light-emitting applications. For two-dimensional planar single layer structures, the band gap of g-AlxGa1-xN alloy increase monotonically with the increase of Al concentration. In contrast, for the buckled structures, as Al concentration increases, the band gap of the alloy structure first increase and then decrease, for the Al0.5Ga0.5N alloy, maximum band gap values can be achieved. The ε peaks and absorption coefficients of planar structures blue-shift, but those of the buckled structures red-shift. The absorption coefficients of the two type structures show two distinct absorption peaks in the deep ultraviolet, therefore deep ultraviolet emission is considered to be a remarkable feature of g-AlxGa1-xN alloys, indicating the potential use of g-AlxGa1-xN alloys for future UV luminescence applications.
关键词： g-AlxGa1-xN alloys,Electronic structure,Optical properties,Two-dimensional material,The first principles
更新于2025-09-23 15:19:57
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Layer-dependent signatures for exciton dynamics in monolayer and multilayer WSe2 revealed by fluorescence lifetime imaging measurement
摘要： Two-dimensional (2D) transition-metal dichalcogenide (TMD) materials have aroused noticeable interest due to their distinguished electronic and optical properties. However, little is known about their complex exciton properties together with the exciton dynamics process which have been expected to influence the performance of optoelectronic devices. The process of fluorescence can well reveal the process of exciton transition after excitation. In this work, the room-temperature layer-dependent exciton dynamics properties in layered WSe2 are investigated by the fluorescence lifetime imaging microscopy (FLIM) for the first time. This paper focuses on two mainly kinds of excitons including the direct transition neutral excitons and trions. Compared with the lifetime of neutral excitons (< 0.3 ns within four-layer), trions possess a longer lifetime (~ 6.6 ns within four-layer) which increases with the number of layers. We attribute the longer-lived lifetime to the increasing number of trions as well as the varieties of trion configurations in thicker WSe2. Besides, the whole average lifetime increases over 10% when WSe2 flakes added up from monolayer to four-layer. This paper provides a novel tuneable layer-dependent method to control the exciton dynamics process and finds a relatively longer transition lifetime of trions at room temperature, enabling to investigate in the charge transport in TMD-based optoelectronics devices in the future.
关键词： two-dimensional (2D) WSe2,fluorescence lifetime,fluorescence lifetime imaging microscopy (FLIM),exciton dynamics,density functional theory (DFT)
更新于2025-09-23 15:19:57
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with Optimal Band Gap for Photovoltaics and Defect-Insensitive Blue Emission
摘要： Despite rapid progress in the power-conversion efficiency of Pb-based perovskite solar cells, both the long-term instability and Pb toxicity are still the main challenges for their commercial applications. Here, by first-principles GW calculations, we find three kinds of two-dimensional (2D) 111-type Pb-free In-based halide perovskites of the form Cs3In2X9 (X = Cl, Br, I) as promising alternatives to the star material CH3NH3PbI3 (MAPbI3) because of the following excellent electronic, optical, and transport properties: (i) The 2D In-based halide perovskites are environmentally friendly lead-free materials. (ii) Compared with MAPbX3, they have greater structural stability. (iii) As energetic photovoltaic materials, 2D Cs3In2I9 perovskites are direct-band-gap semiconductors with optimal band gaps from 1.25 eV (trilayer) to 1.47 eV (monolayer). (iv) The 2D Cs3In2X9 perovskites have ideal band structures for solid-state lighting with a wide direct-optical-band-gap range (approximately 0.94–3.54 eV), covering the whole visible-light region, and light electron (heavy hole) effective mass, which will directly enhance the defect-insensitive emission efficiency due to the localization of holes. Particularly, Cs3In2BrxCl9?x has a suitable direct optical band gap for highly desired blue emission. (v) The absorption coefficient of Cs3In2X9 is up to 7 × 104 cm?1, which is between that of GaAs (104 cm?1) and that of MAPbI3 (105 cm?1). (vi) The estimated power-conversion efficiency in Cs3In2I9 reaches 28%, which is close to that of MAPbI3 (30%). These findings pave a way for designing nontoxic, stable, and high-performance photovoltaic and light-emitting devices.
关键词： light-emitting devices,photovoltaics,halide perovskites,lead-free,two-dimensional,first-principles calculations
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