Band alignment in multilayered semiconductor homojunctions supported on metals

Wang, Qian; Dou, Kunpeng; Shi, Xingqiang

doi:10.1039/c9tc04512k

Cited by 19 publications

(7 citation statements)

References 64 publications

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“…Owing to the absence of dangling bonds and trap states on the surface of 2D materials, abrupt heterojunctions with ideal band alignments can be designed as intended. [87,88] It is also possible to realize countless combinations of heterojunction-structures without lattice mismatch constraints, which are difficult to implement in conventional bulk materials. Notably, with the competitive abilities of 2D materials including their atomically thin bodies and electrostatic transparency, heterostructures built from wide range combinations of 2D materials can provide functionally diverse and high-performance devices such as the low-power FETs, [89][90][91] p-n diodes, [43,[92][93][94] and electrically tunable barristors.…”

Section: (11 Of 16)mentioning

confidence: 99%

Memristors Based on 2D Materials as an Artificial Synapse for Neuromorphic Electronics

2020

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of neurons and synapses is necessary. Moreover, the functions of biological synapses, particularly its capability to permit the transmission of time-dependent signals between neurons, are essential to demonstrate spiking neural networks (SNNs) for parallel operations. [4,5] In this regard, artificial synapses mimicking event-driven synaptic behaviors have been demonstrated using various architectures, including complementary metal-oxidesemiconductor transistors, [6] emerging transistors operated by ferroelectric or electrochemical gate coupling, [7-9] and memristors based on non-volatile memories. [10-12] Among these, memristors have been considered as one of the most promising candidates in neuromorphic computing applications owing to their intrinsic capability to remember the historical information of previously supplied electrical signals even with a single unit device. After Chua et al. theoretically proved the existence of a memristor in 1971, [13,14] tremendous efforts have been devoted to its implementation in an electrical device. After a few decades, in 2008, Williams et al. in Hewlett-Packard Laboratories first reported that memristive behavior can be experimentally achieved in an actual device using the Pt/TiO 2 /Pt structure. [15,16] Their memristive switching behaviors are attributed to the migration of oxygen vacancies in the TiO x layer, triggering the gradient change of the doping state. The active TiO x layer is separated into the undoped TiO 2 and doped TiO 2−x layers as bias above the critical limit is applied. Because TiO 2−x has a variable conductivity depending on its composition, the resistance of the device can be step-wisely changed through the applied bias, which induces the memristive phenomenon. Subsequently, there has been a remarkable progress in memristor-based neuromorphic devices. The capability of various material candidates to mimic essential synaptic functions, including short-term plasticity (STP), long-term plasticity (LTP), short-term depression (STD), long-term depression (LTD), paired pulse facilitation (PPF), and spike-time-dependentplasticity (STDP) learning, has been investigated. [17-19] Each function is an essential element for constructing SNNs. In detail, the STP, STD, LTP, and LTD are kinds of neuroplasticity related to short-term and long-term memory, which represents temporal or long-lasting enhancement/decaying of synaptic connections. PPF is a kind of the short-term plasticity, The memristor, a composite word of memory and resistor, has become one of the most important electronic components for brain-inspired neuromorphic computing in recent years. This device has the ability to control resistance with multiple states by memorizing the history of previous electrical inputs, enabling it to mimic a biological synapse in the neural network of the human brain. Among many candidates for memristive materials, including metal oxides, organic materials, and low-dimensional nanomaterials, 2D layered materials have been widely investigated owing to their outstanding phys...

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Section: (11 Of 16)mentioning

confidence: 99%

Memristors Based on 2D Materials as an Artificial Synapse for Neuromorphic Electronics

2020

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“…13,29,49,79,91 The interface formed between surface and bulk phases in AVP samples may therefore be causing a shift in the experimental UPS spectra, raising the apparent experimental Fermi level due to work function alignment at semicoherent interfaces, similar to a transistor junction. 92 The presence of this surface/interface phenomenon is further supported by the sub-band-gap optical transition components shown in the collected UV−vis−NIR reflectance spectra shown in Figure 3d. A clear linear edge present in these sub-band-gap transition regions points to a well-crystallized alkali-ion-deficient phase coexisting at the surface.…”

Section: ■ Discussionmentioning

confidence: 64%

“…Li-, Na-, and K-ion-deficient surface states are likely to present a narrow band gap and lower Fermi level compared to the fully Li-, Na-, and K-ion-intercalated materials. Previous DFT studies of intercalation ion dynamics for LVP and NVP demonstrate that Li- and Na-deficient surface states display a narrower band gap with a shift of the conduction band minimum to lower energies and Fermi levels closer to the conduction band. ,,,, The interface formed between surface and bulk phases in AVP samples may therefore be causing a shift in the experimental UPS spectra, raising the apparent experimental Fermi level due to work function alignment at semicoherent interfaces, similar to a transistor junction . The presence of this surface/interface phenomenon is further supported by the sub-band-gap optical transition components shown in the collected UV–vis–NIR reflectance spectra shown in Figure d.…”

Section: Discussionmentioning

confidence: 99%

Validating the Electronic Structure of Vanadium Phosphate Cathode Materials

Jenkins

Alarco

Cowie

2021

ACS Appl. Mater. Interfaces

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Investigation of the electronic structure of contending battery electrode materials is an essential step for developing a detailed mechanistic understanding of charge–discharge properties. Herein, we use synchrotron soft X-ray absorption spectroscopy (XAS) in combination with complementary experiments and density functional theory calculations to map the electronic structure, band positioning, and band gap of prototype vanadium(III) phosphate cathode materials, Na3V2(PO4)3, Li3V2(PO4)3, and K3V3(PO4)4·H2O, for alkali-ion rechargeable batteries. XAS fluorescence yield and electron yield measurements reveal substantial variation in surface-to-bulk atomic structure, vanadium oxidation states, and density of oxygen hole states across all samples. We attribute this variation to an intrinsic alkali metal surface depletion identified across these alkali metal vanadium(III) phosphates. We propose that an alkali-depleted surface provides a beneficial interface with the bulk structure(s) that raises the Fermi level and improves surface charge transfer kinetics. Furthermore, we discuss how this effect can play a significant role in reducing the electronic and ionic diffusion limitations of alkali vanadium phosphates in alkali-ion rechargeable batteries. These findings clarify the electronic structure and properties of alkali metal vanadium phosphates and offer guidance on future strategies to improve vanadium phosphate battery performance.

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“… 39 The SCAN+rVV10 method has offered a good performance for layered-materials compared with experimental results 40 and is especially appropriate for metal-semiconductor contacts. 41 The Mo 4s and 4p electrons are also taken as valence electrons so that each Mo atom contains 14 valence electrons in the PAW potential. In addition, the plane-wave energy cut-off is taken as 500 eV, and the Brillouin-zone integration of 5 × 5 × 1 Monkhorst–Pack mesh is utilized throughout the geometric relaxations and electronic structure calculations.…”

Section: Methodsmentioning

confidence: 99%

Interface contact and modulated electronic properties by in-plain strains in a graphene–MoS₂ heterostructure

et al. 2023

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Band alignment in multilayered semiconductor homojunctions supported on metals

Abstract: To solve the tough problem of momentum-mismatch in heterojunctions, we propose a universal approach to obtain type II band alignment in two-dimensional semiconductor homojunctions with wide range momentum-space-match by band-nesting effect.

Cited by 19 publications

References 64 publications

Memristors Based on 2D Materials as an Artificial Synapse for Neuromorphic Electronics

Memristors Based on 2D Materials as an Artificial Synapse for Neuromorphic Electronics

Validating the Electronic Structure of Vanadium Phosphate Cathode Materials

Interface contact and modulated electronic properties by in-plain strains in a graphene–MoS₂ heterostructure

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Band alignment in multilayered semiconductor homojunctions supported on metals

Abstract: To solve the tough problem of momentum-mismatch in heterojunctions, we propose a universal approach to obtain type II band alignment in two-dimensional semiconductor homojunctions with wide range momentum-space-match by band-nesting effect.

Cited by 19 publications

References 64 publications

Memristors Based on 2D Materials as an Artificial Synapse for Neuromorphic Electronics

Memristors Based on 2D Materials as an Artificial Synapse for Neuromorphic Electronics

Validating the Electronic Structure of Vanadium Phosphate Cathode Materials

Interface contact and modulated electronic properties by in-plain strains in a graphene–MoS2 heterostructure

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Interface contact and modulated electronic properties by in-plain strains in a graphene–MoS₂ heterostructure