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"Chalcogenides"
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A large-energy-gap oxide topological insulator based on the superconductor BaBiO sub(3)
Topological insulators are a new class of quantum materials that are characterized by robust topological surface states (TSSs) inside the bulk insulating gap, which hold great potential for applications in quantum information and spintronics as well as thermoelectrics. One major obstacle is the relatively small size of the bulk bandgap, which is typically around 0.3eV for the known topological insulator materials (ref. and references therein). Here we demonstrate through ab initio calculations that a known superconductor BaBiO sub(3) (BBO) with a T sub(c) of nearly 30K (refs , ) emerges as a topological insulator in the electron-doped region. BBO exhibits a large topological energy gap of 0.7eV, inside which a Dirac type of TSSs exists. As the first oxide topological insulator, BBO is naturally stable against surface oxidization and degradation, distinct from chalcogenide topological insulators. An extra advantage of BBO lies in its ability to serve as an interface between TSSs and superconductors to realize Majorana fermions for future applications in quantum computation.
Journal Article
Composition and phase engineering of metal chalcogenides and phosphorous chalcogenides
Two-dimensional (2D) materials with multiphase, multielement crystals such as transition metal chalcogenides (TMCs) (based on V, Cr, Mn, Fe, Cd, Pt and Pd) and transition metal phosphorous chalcogenides (TMPCs) offer a unique platform to explore novel physical phenomena. However, the synthesis of a single-phase/single-composition crystal of these 2D materials via chemical vapour deposition is still challenging. Here we unravel a competitive-chemical-reaction-based growth mechanism to manipulate the nucleation and growth rate. Based on the growth mechanism, 67 types of TMCs and TMPCs with a defined phase, controllable structure and tunable component can be realized. The ferromagnetism and superconductivity in FeXy can be tuned by the y value, such as superconductivity observed in FeX and ferromagnetism in FeS2 monolayers, demonstrating the high quality of as-grown 2D materials. This work paves the way for the multidisciplinary exploration of 2D TMPCs and TMCs with unique properties.A competitive-chemical-reaction-based growth mechanism by controlling the kinetic parameters can easily realize the growth of transition metal chalcogenides and transition metal phosphorous chalcogenides with different compositions and phases.
Journal Article
EXPLORING THE TUNABILITY IN OPTICAL BANDGAP OF Ge15Se70Te10Sb5 CHALCOGENIDE GLASS
In this work, the optical bandgap variations of the chalcogenide glass Ge15Se70Te5Sb10 in bulk, thin film, and nanocolloid form were explored. The bulk glass was synthesized through a conventional melt quenching method, while the thin film was produced by thermal evaporation, and the nanocolloid was obtained through solution-processed techniques. Optical bandgap measurements for each form, performed via UV-VIS-NIR spectroscopy, revealed a notable blue shift in the bandgap when transitioning from bulk to film and then to nanocolloid. The shift in optical band gap with dimensionality of the material underscores the tunable nature of the bandgap in chalcogenide glasses, presenting potential applications in photonic devices.
Journal Article
Memristive Devices Based on Two-Dimensional Transition Metal Chalcogenides for Neuromorphic Computing
HighlightsBased on the benefits of two-dimensional (2D) transition metal chalcogenides (TMC) materials, the operating concepts and basics of memristors for neuromorphic computing are introduced.The prospects of 2D TMC materials and heterostructures are reviewed, as well as the state-of-the-art demonstration of 2D TMCs-based memristors for neuromorphic computing applications.The most recent advances, current challenges, and future prospects for the manufacture and characterization of memristive neuromorphic devices based on 2D TMCs are discussed.Two-dimensional (2D) transition metal chalcogenides (TMC) and their heterostructures are appealing as building blocks in a wide range of electronic and optoelectronic devices, particularly futuristic memristive and synaptic devices for brain-inspired neuromorphic computing systems. The distinct properties such as high durability, electrical and optical tunability, clean surface, flexibility, and LEGO-staking capability enable simple fabrication with high integration density, energy-efficient operation, and high scalability. This review provides a thorough examination of high-performance memristors based on 2D TMCs for neuromorphic computing applications, including the promise of 2D TMC materials and heterostructures, as well as the state-of-the-art demonstration of memristive devices. The challenges and future prospects for the development of these emerging materials and devices are also discussed. The purpose of this review is to provide an outlook on the fabrication and characterization of neuromorphic memristors based on 2D TMCs.
Journal Article
Electrical suppression of all nonradiative recombination pathways in monolayer semiconductors
Defects in conventional semiconductors substantially lower the photoluminescence (PL) quantum yield (QY), a key metric of optoelectronic performance that directly dictates the maximum device efficiency. Two-dimensional transition-metal dichalcogenides (TMDCs), such as monolayer MoS₂, often exhibit low PL QY for as-processed samples, which has typically been attributed to a large native defect density. We show that the PL QY of as-processed MoS₂ and WS₂ monolayers reaches near-unity when they are made intrinsic through electrostatic doping, without any chemical passivation. Surprisingly, neutral exciton recombination is entirely radiative even in the presence of a high native defect density. This finding enables TMDC monolayers for optoelectronic device applications as the stringent requirement of low defect density is eased.
Journal Article
Approaching the quantum limit in two-dimensional semiconductor contacts
The development of next-generation electronics requires scaling of channel material thickness down to the two-dimensional limit while maintaining ultralow contact resistance
1
,
2
. Transition-metal dichalcogenides can sustain transistor scaling to the end of roadmap, but despite a myriad of efforts, the device performance remains contact-limited
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–
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. In particular, the contact resistance has not surpassed that of covalently bonded metal–semiconductor junctions owing to the intrinsic van der Waals gap, and the best contact technologies are facing stability issues
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,
7
. Here we push the electrical contact of monolayer molybdenum disulfide close to the quantum limit by hybridization of energy bands with semi-metallic antimony (
01
1
̅
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) through strong van der Waals interactions. The contacts exhibit a low contact resistance of 42 ohm micrometres and excellent stability at 125 degrees Celsius. Owing to improved contacts, short-channel molybdenum disulfide transistors show current saturation under one-volt drain bias with an on-state current of 1.23 milliamperes per micrometre, an on/off ratio over 10
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and an intrinsic delay of 74 femtoseconds. These performances outperformed equivalent silicon complementary metal–oxide–semiconductor technologies and satisfied the 2028 roadmap target. We further fabricate large-area device arrays and demonstrate low variability in contact resistance
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threshold voltage, subthreshold swing, on/off ratio, on-state current and transconductance
13
. The excellent electrical performance, stability and variability make antimony (
01
1
̅
2
) a promising contact technology for transition-metal-dichalcogenide-based electronics beyond silicon.
The electrical contact of two-dimensional transistors is pushed close to the quantum limit by hybridization of the energy bands with antimony; the contacts have low contact resistance and excellent stability.
Journal Article
Semiconductor moiré materials
Moiré materials have emerged as a platform for exploring the physics of strong electronic correlations and non-trivial band topology. Here we review the recent progress in semiconductor moiré materials, with a particular focus on transition metal dichalcogenides. Following a brief overview of the general features in this class of materials, we discuss recent theoretical and experimental studies on Hubbard physics, Kane–Mele–Hubbard physics and equilibrium moiré excitons. We also comment on the future opportunities and challenges in the studies of transition metal dichalcogenide and other semiconductor moiré materials.This Review elaborates on the recent developments and the future opportunities and challenges of fundamental research on semiconductor moiré materials, with a particular focus on transition metal dichalcogenides.
Journal Article