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Volatile amines in breath act as biomarkers for kidney and liver diseases. Monitoring these amines, especially when present as a mixture, provides insights into the metabolic state of the body. This study focuses on differentiating volatile amines by systematically modulating the conductivity and sensitivity of WSe2/Multiwalled Carbon Nanotubes composite‐based sensors. The fabricated chemiresistive sensor array demonstrates high selectivity, sensitivity (7.67% ppm−1), fast response and recovery kinetics (32 s/137 s), and accurate discrimination among target amines, even in the presence of other VOCs (volatile organic compounds). The sensor array operates at room temperature and achieves a theoretical limit of detection (LOD) of 387 ppt, 206, 157, and 202 ppb for triethylamine (TEA), dimethylamine (DMA), methylamine (MA), and ammonia (NH3), respectively, demonstrating its suitability for breath sensing and diagnostics. Machine learning (ML) analysis is employed to differentiate between the volatile amines and mixtures with 94% accuracy. The ability to detect these amines at such low ppt and ppb levels underscores the potential of this e‐nose technology for high‐performance applications in early‐stage disease diagnostics. [ABSTRACT FROM AUTHOR]

This study presents a comprehensive simulation of a TiSe2‐based photodetector, an optoelectronic device adept at converting a spectrum of electromagnetic radiation spanning ultraviolet (UV), visible, and infrared wavelengths into electrical signals. The TiSe2 absorber material is characterized by a narrow direct bandgap of 1.2 eV, endowing the photodetector with superior optical and electronic attributes that enhance its photodetection capabilities. In‐depth analysis of the energy band diagram, the current‐voltage (J‐V) characteristics, and spectral responses is conducted. This article involves in methodical variations in the thickness, doping levels, and defect density across different layers to achieve optimal performance. The photodetector's current, JSC, and voltage, VOC are recorded at 37.30 mA cm−2 and 0.795 V, in turn. Additionally, the device achieves a peak responsivity, R of 0.67 A W−1 and a detectivity, D* of 12.9 × 1014 Jones at a wavelength of 920 nm. Notably, the spectral response is significantly enhanced between 760 and 1010 nm, indicating the photodetector's proficient detection of near‐infrared (NIR) light. The findings underscore the potential of TiSe2 as an effective material for photodetector applications, marking a significant advancement in the field and paving the way for future research endeavors in photodetector technology. [ABSTRACT FROM AUTHOR]

In this paper, the first‐principles method is used to calculate the electronic structure of the intrinsic WSe2 system and the Ca adsorbed WSe2 system under shear deformation, and the diffusion barrier of Ca on WSe2 is studied in depth. The results show that shear deformation can effectively reduce the band gap of WSe2 system, and shear deformation can easily lead to the transition from semiconductor properties to metal properties. The adsorption of Ca leads to the change of the band structure of WSe2. The contribution of Ca‐d electrons leads to an increase in the peak in the range of 3–6 eV. The shear deformation reduces the diffusion barrier of Ca on the WSe2 surface. This paper provides an improvement method for the application of WSe2 in the field of battery. [ABSTRACT FROM AUTHOR]

Semi‐floating gate field‐effect transistors (SFG‐FETs) based on 2D materials have received much attention due to their unique optoelectronic characteristics, potential applications in near‐memory computing and constructing sensing‐memory‐processing units. Here, the non‐volatile and gate‐controlled multistate photovoltaic response of a WSe2/h‐BN/graphene SFG‐FET is investigated both in experimental and theoretical aspects. Due to the ambipolar carrier transport of WSe2 channel, both electrons and holes can be stored in the graphene floating gate layer, which results in two evident memory windows on the round sweep transfer characteristic curve. Different charge‐stored states of the SFG layer enable the channel to form a lateral junction that can be adjusted by the gate voltage, which leads to the gate‐controlled multistate photovoltaic response. A theoretical model is implemented to explain the memory and the multistate photovoltaic response behaviors in a quasi‐quantitative level. The relationship between the charge‐stored states in the SFG and the photo‐response, as well as its dependence on the gate voltage are systematically analyzed. These research results provide a reliable way for realizing high‐performance multi‐functional photodetectors based on SFG‐FETs and for thorough understanding the complicated optoelectronic behaviors of SFG‐FETs. [ABSTRACT FROM AUTHOR]

Narrow bandgap 2D layered material platinum selenide (PtSe2) with good environmental stability, high carrier mobility, and high light absorption, has been widely investigated for uncooled midwave‐infrared (MWIR) photodetection. However, the phototransistor based on the PtSe2 operation at room temperature suffered from the high dark current and background noise. Here, a graphene (G)‐enhanced G‐WSe2/PtSe2 hetero‐diode placed on a metal electrode is reported. To enhance the photogain, a graphene layer placed on the WSe2/PtSe2 heterodiode as a local gating layer is designed. The device exhibits an ultra‐high light on/off ratio of up to 108 and ultra‐fast photoresponse speed with raising time τr = 0.9 µs and decay time of τd = 1.5 µs in the visible spectra range. Notably, ultrabroad band photoresponse from 405 to 3366 nm is demonstrated under the self‐power model. Notably, the device presented a competitive photovoltaic effect with a high energy conversion efficiency (PCE) of 3.45%. The results pave the way toward a new approach to tuning the performance of the atomic thin layered materials photodetector. [ABSTRACT FROM AUTHOR]

Chemical modification is a powerful strategy for tuning the electronic properties of 2D semiconductors. Here we report the electrophilic trifluoromethylation of 2D WSe2 and MoS2 under mild conditions using the reagent trifluoromethyl thianthrenium triflate (TTT). Chemical characterization and density functional theory calculations reveal that the trifluoromethyl groups bind covalently to surface chalcogen atoms as well as oxygen substitution sites. Trifluoromethylation induces p‐type doping in the underlying 2D material, enabling the modulation of charge transport and optical emission properties in WSe2. This work introduces a versatile and efficient method for tailoring the optical and electronic properties of 2D transition metal dichalcogenides. [ABSTRACT FROM AUTHOR]

Transition metal dichalcogenides (TMDCs) are a promising class of two‐dimensional (2D) materials for flexible electronic applications due to their low integration temperature, good electronic properties, and excellent mechanical flexibility. Moreover, TMDCs offer the possibility of co‐integrating both n‐ and p‐type transistors on the same substrate, enabling the realization of complementary metal‐oxide‐semiconductor (CMOS) circuits. In this study, n‐type MoS2 field‐effect transistors (FETs), and p‐type WSe2‐FETs integrated on a flexible foil substrate fabricated by standard thin‐film technology are presented. These devices exhibit high stability in their electronic operation under strain and repeated bending cycles. A CMOS inverter based on these transistors is also successfully demonstrated, which shows excellent switching behaviour with high gain (up to 100), high noise margin (0.87 · VDD), and low average static power consumption (40 pW). [ABSTRACT FROM AUTHOR]

Transition metal dichalcogenides (TMDCs) are a promising class of two‐dimensional (2D) materials for flexible electronic applications due to their low integration temperature, good electronic properties, and excellent mechanical flexibility. Moreover, TMDCs offer the possibility of co‐integrating both n‐ and p‐type transistors on the same substrate, enabling the realization of complementary metal‐oxide‐semiconductor (CMOS) circuits. In this study, n‐type MoS2 field‐effect transistors (FETs), and p‐type WSe2‐FETs integrated on a flexible foil substrate fabricated by standard thin‐film technology are presented. These devices exhibit high stability in their electronic operation under strain and repeated bending cycles. A CMOS inverter based on these transistors is also successfully demonstrated, which shows excellent switching behaviour with high gain (up to 100), high noise margin (0.87 · VDD), and low average static power consumption (40 pW). [ABSTRACT FROM AUTHOR]

It is impossible to imagine modern electronic circuitry without a p–n junction—an essential building block for transistors, rectifiers, amplifiers, photovoltaics, etc. Conventional fabrication processes (ion implantation or chemical diffusion) result in an immutable potential configuration depriving reconfigurability. In contrast, the superior electrostatic tunability, dangling bonds‐ and reconstruction‐free interfaces are some of the key features of 2D based heterostructures, making them promising candidates for cutting‐edge optoelectronic and memory applications. Herein, the intercoupled 2D ferroelectricity of 훼‐In2Se3 is utilized to introduce micron‐scale, non‐volatile electrostatic doping in ambipolar WSe2, enabling reconfigurable p–n junction. The actuation mechanism is based on the strong polarization field along the edge topology of In2Se3. The fabricated device presents stable p–n to n–p switching, a superior rectification ratio of ≈106, and a low leakage current of ≈10−12 A. Furthermore, the switchable short‐circuit current response is utilized to demonstrate a novel self‐powered, non‐volatile memory based on photovoltaic reading. The ferroelectric non‐volatility coupled with the ability to control the device operation using optical and electrical signals paves the way for ultrathin energy‐efficient, multi‐level optoelectronic and in‐memory logic devices. [ABSTRACT FROM AUTHOR]

Photodetectors that can achieve high‐speed photoresponse and high responsivity with broadband detection are essential for bio‐health monitoring, imaging, chemical sensing, and many other applications. Herein a high‐performance inorganic–organic hybrid photodetector based on a heterojunction of exfoliated 2D tungsten diselenide (WSe2) layers and solution‐processable poly(3‐hexylthiophene‐2,5‐diyl), P3HT is reported. The heterojunction shows enhanced exciton harvesting through long‐range energy transfer from P3HT to WSe2, which is confirmed using photoluminescence quenching and fluorescence decay measurements. The detector shows broadband light detection from visible to near‐infrared (NIR) (400−1100 nm), and air‐stable device performance. The device exhibits the highest responsivity of 17.6 AW−1 for low incident light intensity (<10−5 W cm−2) at 640 nm wavelength of light. Furthermore, a fast photoresponse speed with a rise/fall time of 9.5/5.1 µs, which retained its performance for more than four months under ambient conditions is demonstrated. The superior device performance presented here using an inorganic–organic hybrid heterojunction is the key to producing novel high‐performance and air‐stable photodetectors with broad spectral bandwidth. [ABSTRACT FROM AUTHOR]

Non-destructive and reversible modulations of polarity and carrier concentration in transistors are essential for complementary devices. The fabricated multi-gated WSe2 devices obtain dynamic electrostatic field induced electrically configurable functions and demonstrate as diode with high rectification ratio of 4.1 × 105, as well as n- and p-type inverter with voltage gain of 19.9 and 12.1, respectively. Benefiting from the continuous band alignment induced modulation of channel underneath the dual gates, the devices exhibit high-performance photodetection in wide spectral range. The devices yield high photo-responsivity (5.16 A W-1) and large 'light/'dark ratio (1 × 105). Besides, the local gate fields accelerate the separation of photo-induced carriers, leading to fast response without persistent current. This strategy takes the advantage of the simplified design and continues to deliver integrated circuits with high density. The superior electrical and photodetection characteristics exhibit great potency in the domain of future optoelectronics. [ABSTRACT FROM AUTHOR]

Machine vision systems that capture images for visual inspection and recognition tasks must be able to perceive, memorize, and compute any color scene. To achieve this, most of the current visual systems use circuits and algorithms which may reduce efficiency and increase complexity. Herein, a 2D semiconductor tungsten diselenide (WSe2)‐based phototransistor that successfully demonstrates an artificial vision system integrating the processing capability of visual information sensing memory, is reported. Furthermore, based on a 6 × 6 fabricated retinal perception array, artificial visual information sensing memory and processing system are proposed to perform image recognition tasks, which can avoid the time delay and energy consumption caused by data conversion and movement. On the other hand, highly linear symmetric synaptic plasticity can be achieved based on the modulation of carrier types in WSe2 transistors with different thicknesses, facilitating the high level of training and inference accuracy for artificial neural networks. Last, through training and inference simulations, the feasibility of the hybrid synapses for optical neural networks (ONN) is demonstrated. [ABSTRACT FROM AUTHOR]

2D transition metal dichalcogenides (TMDCs) are atomically‐thick semiconductors with great potential for next‐generation optoelectronic applications, such as transistors and sensors. Their large surface‐to‐volume ratio makes them energy‐efficient but also extremely sensitive to the physical‐chemical surroundings. The latter must be carefully considered when predicting the electronic behavior, such as their energy level alignment, which ultimately affects the charge carrier injection and transport in devices. Here, local doping is demonstrated and thus adjusting the opto‐electronic properties of monolayer TMDCs (WSe2 and MoS2) by chemically engineering the surface of the supporting substrate. This is achieved by decorating the substrate by microcontact printing with patterns of two different self‐assembled monolayers (SAMs). The SAMs posses distinct molecular dipoles and dielectric constants, significantly influencing the TMDCs electronic and optical properties. By analyzing (on various substrtates), it is confirmed that these effects arise solely from the interaction between SAMs and TMDCs. Understanding the diverse dielectric environments experienced by TMDCs allows for a correlation between electronic and optical behaviours. The changes primarily involve alteration in the electronic band gap width, which can be calculated using the Schottky‐Mott rule, incorporating the dielectric screening of the TMDCs surroundings. This knowledge enables accurate prediction of the (opto‐)electronic behavior of monolayer TMDCs for advanced device design. [ABSTRACT FROM AUTHOR]

High‐performing 2D electrical and optical devices can be realized by forming an ideal van der Waals (vdW) metal contact with weak interactions and stable interface states. However, the methods for applying metal contacts while avoiding damage from metal deposition present challenges in realizing a uniform, stable vdW interface. To overcome this problem, this study develops a method for forming vdW contacts using a sacrificial Se buffer layer. This study explores this method by investigating the difference in the Schottky barrier height between the vdW metal contact deposited using a buffer layer, a transferred metal contact, and a conventional directly deposited metal contact using rectification and photovoltaic characteristics of a Schottky diode structure with graphite. Evidently, the Se buffer layer method forms the most stable and ideal vdW contact while preventing Fermi‐level pinning. A tungsten diselenide Schottky diode fabricated using these vdW contacts with Au and graphite as the top and bottom electrodes, respectively, exhibits excellent operation with an ideality factor of ≈1, an on/off ratio of > 107, and coherent properties. Additionally, when using only the vdW Au contact, the electrical and optical properties of the device can be minutely modulated by changing the structure of the Schottky diode. [ABSTRACT FROM AUTHOR]

Few‐layer transition metal dichalcogenides (TMDs) and their combination as van der Waals heterostructures provide a promising platform for high‐performance optoelectronic devices. However, the ultrathin thickness of TMD flakes limits efficient light trapping and absorption, which triggers the hybrid construction with optical resonant cavities for enhanced light absorption. The optical structure enriched photodetectors can also be wavelength‐ and polarization‐sensitive but require complicated fabrication. Herein, a new‐type TMD‐based photodetector embedded with nanoslits is proposed to enhance light trapping. Taking ReS2 as an example, strong anisotropic Mie‐type optical responses arising from the intrinsic in‐plane anisotropy and nanoslit‐enhanced anisotropy are discovered. Owing to the nanoslit‐enhanced optical resonances and band engineering, excellent photodetection performances are demonstrated with high responsivity of 27 A W−1 and short rise/decay times of 3.7/3.7 ms. More importantly, through controlling the angle between the nanoslit orientation and the polarization direction to excite different resonant modes, polarization‐sensitive photodetectors with anisotropy ratios from 5.9 to 12.6 can be achieved, representing one of the most polarization‐sensitive TMD‐based photodetectors. The depth and orientation of nanoslits are demonstrated crucial for optimizing the anisotropy ratio. The findings bring an effective scheme to construct high‐performance and polarization‐sensitive photodetectors. [ABSTRACT FROM AUTHOR]

This article presents an enormously effective Cu2ZnSnS4 (CZTS)‐based n‐ZnS/p‐CZTS/p+‐WSe2 thin film solar cell. The device has been studied by varying the thickness, doping concentration and defect density of each layer utilizing SCAPS‐1D simulation software. The power conversion efficiency (PCE) for n‐ZnS/p‐CZTS single heterojunction is 14.06% with the JSC = 20.26 mA cm−2, VOC = 0.88 V and FF = 78.59%, respectively. This PCE is elevated to 27.31% with the JSC = 33.72 mA cm−2, VOC = 0.97 V and FF = 83.75%, respectively due to insertion of WSe2 back surface field (BSF) layer in the same structure. The significant improvement of PCE mainly depends on short circuit current which is resulted due to WSe2 layer that absorbs sub‐band gap photons through tail‐states‐assisted (TSA) photon upconversion method. These entire results demonstrate the potential of WSe2 as BSF layer in CZTS‐based thin film solar cells. [ABSTRACT FROM AUTHOR]

BACKGROUND: The construction of a heterojunction is an effective strategy to enhance the activity of a photocatalyst. RESULTS: WSe2/In2S3 photocatalysts with favorable photostability and reusability were prepared via a hydrothermal method. The structural and morphological features of WSe2/In2S3 were investigated using scanning electron microscopy and transmission electron microscopy. Photocatalytic performance of WSe2/In2S3 was tested by the degradation of methylene blue (MB) under visible light. The optimal degradation rate of MB by WSe2/In2S3 reached 92% within 120 min. After eight regeneration cycles, the degradation of WSe2/In2S3 still reached 70% and exhibited good photocatalytic stability. CONCLUSION: The enhanced photocatalytic activity is attributed to the formation of heterostructure of WSe2/In2S3, which could effectively separate the photogenerated e−–h+ pairs. Meanwhile, the photocatalytic degradation intermediates of MB by WSe2/In2S3 heterostructure was investigated by liquid chromatography–mass spectrometry. The results show that the obtained WSe2/In2S3 photocatalyst has a promising practical application. © 2022 Society of Chemical Industry (SCI). [ABSTRACT FROM AUTHOR]

Defects usually play an important role in the modification of the properties of materials. In this investigation, atom vacancy and atomic reorganization defects in various heterostructures obtained using different pristine (or defect‐free) and defective transition metal dichalcogenides (TMDCs) with pristine and defective graphene have been studied using density functional theory (DFT) calculation. Results reveal that: (i) the contact of pristine and defective graphene with various pristine and defective TMDCs is energetically stable, (ii) the stability of these heterostructures driven by dispersion interaction, (iii) the presence of defect significantly influences the work function of the resulting heterostructure, (iv) the pristine graphene/pristine TMDCs heterostructures are metallic in nature with large Schottky barrier (ΦSBH), (v) the heterostructures involving defective graphene are direct band gap semiconductors, (vi) the heterostructures involving defective WS2 are also direct band gap semiconductors, and (vii) the SW defective graphene with pristine WS2/WSe2 forms type‐II heterojunction. [ABSTRACT FROM AUTHOR]

Tin (Sn)‐based perovskites with favorable optoelectronic properties and ideal bandgaps have emerged as promising alternatives to toxic lead (Pb)‐based perovskites for photovoltaic applications. However, it is challenging to obtain high‐quality Sn‐based perovskite films by solution process. Here, liquid‐exfoliated 2D transition‐metal dichalcogenides (i.e., MoS2, WS2, and WSe2) with smooth and defect‐free surfaces are applied as growth templates for spin‐coated FASnI3 perovskite films, leading to van der Waals epitaxial growth of perovskite grains with a growth orientation along (100). The authors find that WSe2 has better energy alignment with FASnI3 than MoS2 and WS2 and results in a cascade band structure in resultant perovskite solar cells (PSCs), which can facilitate hole extraction and suppress interfacial charge recombination in the devices. The WSe2‐modified PSCs show a power conversion efficiency up to 10.47%, which is among the highest efficiency of FASnI3‐based PSCs. The appealing solution phase epitaxial growth of FASnI3 perovskite on 2D WSe2 flakes is expected to find broad applications in optoelectronic devices. [ABSTRACT FROM AUTHOR]

Benefiting from the superior electron mobility and good air‐stability, the emerging layered bismuth oxyselenide (Bi2O2Se) nanosheet has received considerable attention with the promising prospects for electronics and optoelectronics applications. However, the high charge carrier concentration and bolometric effect of Bi2O2Se give rise to the high dark current and relatively slow photoresponse, which severely impede further improvement of the performance of Bi2O2Se based photodetectors. Here, a WSe2/Bi2O2Se Van der Waals p‐n heterostructure is reported with a pronounced rectification ratio of 105 and a low reverse dark current of 10−11 A, as well as an enhanced light on/off ratio up to 618 under 532 nm light illumination. The device also exhibits a fast response speed of 2.6 µs and a broadband detection capability from 365 to 2000 nm due to the efficient charge separation and strong interlayer coupling at the interface of the two flakes. Importantly, the built‐in potential in the WSe2/Bi2O2Se heterostructure offers a competitive self‐powered photodetector with the light on/off ratio above 105 and a photovoltaic responsivity of 284 mA W−1. The WSe2/Bi2O2Se heterostructure shows promising potentials for high‐performance self‐driven photodetector applications. [ABSTRACT FROM AUTHOR]

Van der Waals (vdW) layered materials are promising channel materials for next‐generation field‐effect transistors (FETs). However, in vdW layered‐material FETs, the Schottky barrier and tunnel barrier at the vdW interfaces significantly reduce the electron injection efficiencies at electrical contacts, thereby limiting the development of high‐speed and low‐power FETs. This study demonstrates that intercalated lithium (Li) ions at vdW interfaces lower the Schottky and tunnel barriers at the electrical contacts of multilayer tungsten diselenide FETs owing to the low potential energy of Li and the mild electron doping from intercalation, thus decreasing the resistance at the vdW interfaces and enhancing the current flow and field‐effect mobility. Compared with before‐Li intercalation, the multilayer WSe2 planar FET demonstrates ≈1000 times higher current (IDS = 17.8 μA) at VGS = 50 V, ≈110 times higher maximum field‐effect mobility (μFE = 97.67 cm2 V−1 s−1), and ≈1000 times higher on/off current ratio (on/off ratio = ≈107). Furthermore, in multilayer WSe2 vertical FETs with vdW heterostructures having a structural strength of approximately the same as the current density, the intercalated Li ions at the graphene/WSe2 vdW interfaces additionally improves the current density and the vertical mobility by ≈20 times (1.00 A cm−2) and 10 times (2.52 × 10−4 cm2 V−1 s−1), respectively. This study establishes a method to reduce the resistance at vdW interfaces for developing high‐speed and low‐power multilayer vdW material FETs. [ABSTRACT FROM AUTHOR]

Summary: The behaviour of palladium and nickel deposited on mechanically exfoliated samples of 2D transition metal dichalcogenides (MoS2, WS2 and WSe2) via e‐beam evaporation was investigated. Sputtering of metals on the 2D flakes allowed for interaction of the metal and TMD to be investigated on the Å scale in an aberration‐corrected transmission electron microscope. Through low energy sputtering, metals can be deposited on 2D materials without causing damage to the thin flakes. The material's interaction is investigated on the atomic scale via high resolution scanning transmission electron microscopy in high angle annular dark‐field imaging. Initially, the effect of thermal annealing on the stability of the Pd–2D interaction was investigated, revealing the remarkable difference in particle stability between the 2D materials. Nickel deposition however only resulted in oxidised amorphous particles. The oxide particles' cross‐sectional area and circularity were independent of the TMD substrate thickness, type, or deposition rate. Lay Description: Understanding the interaction between metals and 2D materials is imperative for future device functionalisation. Palladium and nickel were deposited on samples of 2D transition metal dichalcogenides (MoS2, WS2 and WSe2) via e‐beam evaporation. Low energy introduced metal to the 2D materials without causing damage to the thin flakes. The metal–2D interaction was investigated on the Å scale via high resolution scanning transmission electron microscopy in high angle annular dark‐field imaging. The interaction between the Pd and the 2Ds was investigated to see whether Pd is a viable contact solution for TMD materials and to study the metal–2D interaction at the atomic level. Effect of annealing and heat on the stability of the Pd–2D interaction was investigated, showing Pd–WSe2 to have high particle stability up to 200 °C. In contrast, the Pd–MoS2 and Pd–WS2 had lower particle stability when heated, revealing particle agglomeration and changes. Nickel was found to oxidise into amorphous oxide particles quickly after deposition. The oxide particles' characteristics were independent of the TMD substrate thickness andtype, and independent of the rate at which metal was deposited. [ABSTRACT FROM AUTHOR]

It is generally accepted that perpendicular magnetic anisotropy (PMA) magnets are preferred over in‐plane magnetic anisotropy (IMA) magnets in data storage applications owing to their large thermal stability even at ultra‐scaled dimensions. To efficiently and deterministically switch a PMA, out‐of‐plan spin current is required. However, conventional giant spin Hall effect (GSHE) materials only produce spin currents with in‐plane polarization. Our work, on the other hand, demonstrated for the first time that out‐of‐plane spin currents can indeed be generated by applying electric filed to monolayer WSe2 at room temperature and the spin information was detected by a graphene channel. Supported by theoretical calculations, we found that the interfacial polarization between graphene and WSe2 to be ~38% assuming the ferromagnetic detector's polarization efficiency to be ~4%. Moreover, the spin polarization is determined by the polarity of the applied electric field. [ABSTRACT FROM AUTHOR]

Abstract: Benefiting from the technique of vertically stacking 2D layered materials (2DLMs), an advanced novel device architecture based on a top‐gated MoS2/WSe2 van der Waals (vdWs) heterostructure is designed. By adopting a self‐aligned metal screening layer (Pd) to the WSe2 channel, a fixed p‐doped state of the WSe2 as well as an independent doping control of the MoS2 channel can be achieved, thus guaranteeing an effective energy‐band offset modulation and large through current. In such a device, under specific top‐gate voltages, a sharp PN junction forms at the edge of the Pd layer and can be effectively manipulated. By varying top‐gate voltages, the device can be operated under both quasi‐Esaki diode and unipolar‐Zener diode modes with tunable current modulations. A maximum gate‐coupling efficiency as high as ≈90% and a subthreshold swing smaller than 60 mV dec−1 can be achieved under the band‐to‐band tunneling regime. The superiority of the proposed device architecture is also confirmed by comparison with a traditional heterostructure device. This work demonstrates the feasibility of a new device structure based on vdWs heterostructures and its potential in future low‐power electronic and optoelectronic device applications. [ABSTRACT FROM AUTHOR]

Highly linearly symmetric synaptic plasticity can be achieved based on the modulation of carrier types in WSe SB 2 sb with different thicknesses, facilitating a high level of training accuracy for optical neural networks. Keywords: artificial vision system; in-sensor computing; memory; optical neural networks; WSe2 EN artificial vision system in-sensor computing memory optical neural networks WSe2 1 1 1 10/12/23 20231009 NES 231009 B Bioinspired Artificial Visual System b In article number 2303539, Ye Zhou, Su-Ting Han, and co-workers report a 2D WSe SB 2 sb -based retinal perception array that demonstrates an artificial vision system integrating sense and memory visual information. Artificial vision system, in-sensor computing, memory, optical neural networks, WSe2. [Extracted from the article]

This report presents a simple and efficient method of layer thinning and p-type doping of WSe2 with vapor XeF2. With this approach, the surface roughness of thinned WSe2 can be controlled to below 0.7 nm at an etched depth of 100 nm. By selecting appropriate vapor XeF2 exposure times, 23-layer and 109-layer WSe2 can be thinned down to monolayer and bilayer, respectively. In addition, the etching rate of WSe2 exhibits a significant dependence on vapor XeF2 exposure pressure and thus can be tuned easily for thinning or patterning applications. From Raman, photoluminescence, X-ray photoelectron spectroscopy (XPS), and electrical characterization, a p-doping effect of WSe2 induced by vapor XeF2 treatment is evident. Based on the surface composition analysis with XPS, the causes of the p-doping effect can be attributed to the presence of substoichiometric WO x ( x < 3) overlayer, trapped reaction product of WF6, and nonstoichiometric WSe x ( x > 2). Furthermore, the p-doping level can be controlled by varying XeF2 exposure time. The thinning and p-doping of WSe2 with vapor XeF2 have the advantages of easy scale-up, high etching selectivity, excellent controllability, and compatibility with conventional complementary metal-oxide-semiconductor fabrication processes, which is promising for applications of building WSe2 devices with versatile functionalities. [ABSTRACT FROM AUTHOR]

This report presents a simple and efficient method of layer thinning and p-type doping of WSe2 with vapor XeF2. With this approach, the surface roughness of thinned WSe2 can be controlled to below 0.7 nm at an etched depth of 100 nm. By selecting appropriate vapor XeF2 exposure times, 23-layer and 109-layer WSe2 can be thinned down to monolayer and bilayer, respectively. In addition, the etching rate of WSe2 exhibits a significant dependence on vapor XeF2 exposure pressure and thus can be tuned easily for thinning or patterning applications. From Raman, photoluminescence, X-ray photoelectron spectroscopy (XPS), and electrical characterization, a p-doping effect of WSe2 induced by vapor XeF2 treatment is evident. Based on the surface composition analysis with XPS, the causes of the p-doping effect can be attributed to the presence of substoichiometric WO x ( x < 3) overlayer, trapped reaction product of WF6, and nonstoichiometric WSe x ( x > 2). Furthermore, the p-doping level can be controlled by varying XeF2 exposure time. The thinning and p-doping of WSe2 with vapor XeF2 have the advantages of easy scale-up, high etching selectivity, excellent controllability, and compatibility with conventional complementary metal-oxide-semiconductor fabrication processes, which is promising for applications of building WSe2 devices with versatile functionalities. [ABSTRACT FROM AUTHOR]

High-energy ionizing radiation is widely used in medical diagnosis and cancer radiation therapy. However, high-energy radiation can also impose significant damages in healthy tissues during medical treatments via direct DNA damages and indirect damages from production of reactive oxygen species (ROS). Therefore, it is urgent to develop highly effective radioprotectants with low toxicities that can meet the increasing needs for alleviating the adverse effects from cancer radiation therapy and nuclear emergency. In this work, strongly catalytic ultrasmall (sub-5 nm) cysteine-protected WSe2 dots are employed to protect healthy tissues against radiation via diminishing radiation-induced free radicals. The WSe2 dots with high surface activities can recover radiation-induced DNA damages and eliminate the excessive ROS generated from radiation. In vivo experiments confirm that the survival rate of mice treated with WSe2 dots is significantly elevated with radiation damages postponed under exposure to high-dose ionizing radiation. Furthermore, the free radicals in major organs and hematological system can be appreciably omitted, suggesting their unique role as free radical scavengers. These WSe2 dots in ultrasmall size show rapid renal clearance of ≈74% injection dose via urine excretion in 24 h and do not cause any apparent toxicity in vivo for up to 30 d. [ABSTRACT FROM AUTHOR]

We have investigated the electronic properties of WSe2 surfaces covered by fluorinated cobalt phthalocyanine (F16CoPc) using photoemission spectroscopy. We show that a charge transfer occurs at this interface, which results in the creation of holes in the WSe2 surface while the Co center of the phthalocyanine is reduced to Co(I). We observe a potential change in WSe2 approaching the surface as a consequence of the induced positive charges near the surface. In addition, our data allow for a rough estimation of the induced charge density and suggest that the holes might be localized. [ABSTRACT FROM AUTHOR]

P-type transistors based on high work function transition metal dichalcogenide (TMD) monolayers such as MoS2 are to date difficult to produce, owing to the strong Fermi level pinning at the semiconductor/contact metal interfaces. In this work, the potential of halogenated graphenes is demonstrated as a new class of efficient hole injection layers to TMDs such as MoS2 and WSe2 by taking fluorographene (or GF) as a model buffer layer. Using first-principles computations, two commonly obtained GF stoichiometries, C2F and CF, have been studied as buffer layers between MoS2 and Pt. In particular, for high work function TMDs such as MoS2, it has been shown that C2F forms an ohmic contact, while CF leads to a significant p-SBH value. On the other hand, for low work function TMDs such as WSe2, both C2F and CF lead to p-type ohmic contacts. This analysis shows that the ability of these buffer layers to form p-type contacts depends crucially on the charge redistribution at the GF/metal interface, which is dictated by their chemical interaction and equilibrium geometry. The fundamental electronic structures between the different semiconductor/insulator/metal interfaces which are part of this study have also been investigated. [ABSTRACT FROM AUTHOR]

Optical dipole moment is the key parameter of optical transitions, as it directly determines the strength of light-matter interaction such as intrinsic radiative lifetime. However, experimental determination of these fundamental properties of excitons in monolayer WSe2 is largely limited, because the commonly used measurement, such as (time-resolved) photoluminescence, is inherently difficult to probe the intrinsic properties. For example, dark states below bright exciton can change the photoluminescence emission rate by orders of magnitude and gives an 'effective' radiative lifetime distinctive from the intrinsic one. On the other hand, such 'effective' radiative lifetime becomes important itself because it describes how dark states affect exciton dynamics. Unfortunately, the 'effective' radiative lifetime in monolayer WSe2 is also not determined as it requires photoluminescence measurement with resonant excitation, which is technically difficult. These difficulties are overcome here to obtain both the 'intrinsic' and 'effective' radiative lifetime experimentally. A framework is developed to determine the dipole moment and 'intrinsic' radiative lifetime of delocalized excitons in monolayer WSe2 from the absorption measurements. In addition, the 'effective' radiative lifetime in WSe2 is obtained through time-resolved photoluminescence and absolute quantum-yield measurement at resonant excitation. These results provide helpful information for fundamental understanding of exciton light-matter interaction in WSe2. [ABSTRACT FROM AUTHOR]

Optical dipole moment is the key parameter of optical transitions, as it directly determines the strength of light-matter interaction such as intrinsic radiative lifetime. However, experimental determination of these fundamental properties of excitons in monolayer WSe2 is largely limited, because the commonly used measurement, such as (time-resolved) photoluminescence, is inherently difficult to probe the intrinsic properties. For example, dark states below bright exciton can change the photoluminescence emission rate by orders of magnitude and gives an 'effective' radiative lifetime distinctive from the intrinsic one. On the other hand, such 'effective' radiative lifetime becomes important itself because it describes how dark states affect exciton dynamics. Unfortunately, the 'effective' radiative lifetime in monolayer WSe2 is also not determined as it requires photoluminescence measurement with resonant excitation, which is technically difficult. These difficulties are overcome here to obtain both the 'intrinsic' and 'effective' radiative lifetime experimentally. A framework is developed to determine the dipole moment and 'intrinsic' radiative lifetime of delocalized excitons in monolayer WSe2 from the absorption measurements. In addition, the 'effective' radiative lifetime in WSe2 is obtained through time-resolved photoluminescence and absolute quantum-yield measurement at resonant excitation. These results provide helpful information for fundamental understanding of exciton light-matter interaction in WSe2. [ABSTRACT FROM AUTHOR]

This paper demonstrates the fabrication and operation of a vertically integrated phototransistor based on single‐layer MoS2/multilayer WSe2 van der Waals heterojunction. Under the gate modulation effects, the device which combines advantages of their constituents displays a novel feature in the transfer characteristics where a current peak appears at small gate voltage bias and exhibits excellent optical broadband photodetecting properties. Upon visible light illumination (660 nm), the photodetection capabilities reach the optimal values simultaneously with the photoresponsivity of 17.8 A W−1, photosensivity of 140, and the response speed of <80 ms. The device also shows good photoresponse under near‐infrared light illumination (850 nm) and the obvious dependence on the gate voltage which plays a switching role for near infrared light photodetection. This 2D heterostructured broadband photodetector may provide an available device structure for an essential sensing component in the future wearable electronics applications. [ABSTRACT FROM AUTHOR]

The cross-plane thermal conductivity of WSe2 is investigated using reverse nonequilibrium molecular dynamics (RNEMD) and a recently developed Stillinger-Weber potential. It is found that the cross-plane thermal conductivity of WSe2 is strongly size dependent and saturates around 80 layers. Moreover, it is shown that even at 1000 K, ordered crystalline WSe2 does not reach the phonon glass-like limit in the cross-plane direction. [ABSTRACT FROM AUTHOR]

We studied an evaluation method of photoluminescence (PL) quantum yield of monolayer transition metal chalcogenides (TMDs) on a transparent substrate using a reference dye. A 3-borylbithiophene derivative (C58H49BN2S4) reference dye shows a high PL quantum yield of 36% even in the solid form and the high quantum yield is kept in a Poly(methyl methacrylate) (PMMA) matrix. Moreover, the photon energy of PL is similar to those of monolayer TMDs. These PL characteristics of the reference dye are useful for a evaluation of PL quantum yield in monolayer TMDs. The PL quantum yield of 0.18 ± 0.03% was evaluated for mechanically exfoliated monolayer WSe2 on glass substrate at room temperature. [ABSTRACT FROM AUTHOR]

Two types of transition metal dichalcogenide (TMD) transistors are applied to demonstrate their possibility as switching/driving elements for the pixel of organic light-emitting diode (OLED) display. Such TMD materials are 6 nm thin WSe2 and MoS2 as a p-type and n-type channel, respectively, and the pixel is thus composed of external green OLED and nanoscale thin channel field effect transistors (FETs) for switching and driving. The maximum mobility of WSe2-FETs either as switch or as driver is ≈30 cm2 V−1 s−1, in linear regime of the gate voltage sweep range. Digital (ON/OFF-switching) and gray-scale analogue operations of OLED pixel are nicely demonstrated. MoS2 nanosheet FET-based pixel is also demonstrated, although limited to alternating gray scale operation of OLED. Device stability issue is still remaining for future study but TMD channel FETs are very promising and novel for their applications to OLED pixel because of their high mobility and ID ON/OFF ratio. [ABSTRACT FROM AUTHOR]

The emergence of semiconducting transition metal dichalcogenide (TMD) atomic layers has opened up unprecedented opportunities in atomically thin electronics. Yet the scalable growth of TMD layers with large grain sizes and uniformity has remained very challenging. Here is reported a simple, scalable chemical vapor deposition approach for the growth of MoSe2 layers is reported, in which the nucleation density can be reduced from 105 to 25 nuclei cm−2, leading to millimeter-scale MoSe2 single crystals as well as continuous macrocrystalline films with millimeter size grains. The selective growth of monolayers and multilayered MoSe2 films with well-defined stacking orientation can also be controlled via tuning the growth temperature. In addition, periodic defects, such as nanoscale triangular holes, can be engineered into these layers by controlling the growth conditions. The low density of grain boundaries in the films results in high average mobilities, around ≈42 cm2 V−1 s−1, for back-gated MoSe2 transistors. This generic synthesis approach is also demonstrated for other TMD layers such as millimeter-scale WSe2 single crystals. [ABSTRACT FROM AUTHOR]

Highly (001)-textured tungsten diselenide WSe2 thin films have been prepared by a two-step process on quartz glass and TiN metallic back contacts, respectively. At first, X-ray amorphous, selenium-rich WSe2+ x films were deposited by reactive magnetron sputtering at room temperature onto a thin metal promoter film (Ni or Pd) and afterwards annealed in an H2Se/Ar atmosphere. X-ray diffraction and scanning electron microscopy show that highly (001)-oriented WSe2 films can be grown, which is caused by the formation of liquid promoter-metal selenide droplets which dissolve tungsten or tungsten selenide at temperatures, higher than the eutectic temperature in the promoter metal-selenium system, followed by oversaturation and eventually crystallization of WSe2 platelets. Time-resolved microwave conductivity measurements show that the films are photoactive. The sum of the carrier mobilities of the best films µe + µh is in the range of 1-7 cm2 V−1 s−1. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) layered materials are drawing considerable attention across multiple scientific and engineering disciplines owing to their exquisite electronic, optoelectronic, mechanical and chemical properties. In this article, a short review of our recent work on 2D-electronics will be presented. [ABSTRACT FROM AUTHOR]

Manipulating the bandgap structure and carrier distribution of multilayer transition metal dichalcogenides (TMDs) is crucial for improving their fluorescence efficiency and extending their optoelectronic applications. Herein, the evolution of the conduction band minimum of multilayer WSe2 as a function of the temperature and thickness is experimentally demonstrated and an ≈70‐fold fluorescence enhancement of the K–K direct emission is observed at 560 K in multilayer WSe2 flakes (≈170 nm) by heat engineering. This abnormal enhancement is attributed to thermally driven carrier redistribution achieved via intervalley transfer, which is confirmed by the theoretical calculations and temperature‐dependent time‐resolved photoluminescence. In addition, a threshold temperature of the intervalley transfer is proposed to describe the on‐state of the carrier redistribution model. The corresponding threshold temperature is determined to be ≈580 K, which is consistent with the temperature at which the maximum photoluminescence enhancement is observed. The study provides a useful strategy to optimize the optical and electric performances of multilayer WSe2 and other TMDs materials. [ABSTRACT FROM AUTHOR]

Transition metal oxides (TMOs) with high work function (WF) show promising properties as unipolar p‐type contacts for transition metal dichalcogenides. Here, ambipolar field‐effect transistors (FETs) enabled by bilayer WSe2 with self‐assembled TMOs (WO2.57) as contacts are reported. Systematic material characterizations demonstrate the formation of WO2.57/WSe2 heterojunctions around nanoflake edges with Se atoms substituted by O atoms after air‐exposure, while pristine properties of WSe2 almost sustain in inner domains. As‐fabricated FETs exhibit both polarities, implying WO2.57 with lowered WF at edges can serve as both the p‐type and n‐type contact for inner WSe2. Noteworthy, greatly reduced contact resistance and enhanced channel current are achieved, compared to the devices without WO2.57 contacts. Linear drain–source current relationship from 77 to 300 K indicates the ohmic contact between edge WO2.57 and inner WSe2. Density functional theory calculations further reveal that the WO2.57/WSe2 heterojunction forms a barrier‐less charge distribution. These nm‐scale FETs possess remarkable electrical conductivity up to ≈2600 S m−1, ultra‐low leakage current down to ≈10−12 A, robustness for high voltage operation, and air stability, which even outperform pristine WSe2 FETs. Theoretical calculations reveal that the high conductivity is exclusively attributed to the air‐induced WO2.57 and its further carrier injection to WSe2. [ABSTRACT FROM AUTHOR]

Various functions are introduced from a unique field‐effect device structure which combines or merges transition metal dichalcogenide (TMD) and InGaZnO (IGZO) channels together on one common gate: multivalue field effect transistors (FETs), photodetecting devices, and signal frequency doublers. Judging by the individual transfer characteristics of two FET devices, the n‐IGZO FET always shows higher drain current and more positive‐side turn‐on voltage than those of n‐TMD channel FETs. As a result, a combined transfer characteristic presents two‐step drain current levels, so that their load‐resistance inverter might demonstrate three value output voltage signals. Those ternary value inverter devices with n‐IGZO/n‐ReSe2 or n‐IGZO/n‐WSe2 combination also operate as a photodetector, responding to visible/near infrared (IR) photons with a fast photodynamics of 30 ms rising/falling time. The most interesting is the ambipolar device achieved from n‐IGZO FET/p‐MoTe2 FET combination circuit. The ambipolar device circuit operates as an alternating current (AC) signal frequency doubler and demonstrates twofold organic light emitting diode blinking in one AC period. This unprecedented technique for the multifunctional field effect TMD devices incorporating n‐IGZO FETs will open a new path toward future electronics. [ABSTRACT FROM AUTHOR]

Multi‐valued logic (MVL) computing, which uses more than three logical states, is a promising future technology for handling huge amounts of data in the forthcoming "big data" era. The feasibility of MVL computing depends on the development of new concept devices/circuits beyond the complementary metal oxide semiconductor (CMOS) technology. This is because many CMOS devices are required to implement basic MVL functions, such as multilevel NOT, AND, and OR. In this study, a novel MVL device is reported with a complementarily controllable potential well, featuring the negative differential transconductance (NDT) phenomenon. This NDT device implemented on the WS2–graphene–WSe2 van der Waals heterostructure is evolved to a double‐NDT device operating on the basis of two consecutive NDT phenomena via structural engineering and parallel device configuration. This double‐NDT device is intensively analyzed via atomic force microscopy, kelvin probe force microscopy, Raman spectroscopy, and temperature‐dependent electrical measurement to gain a detailed understanding of its operating mechanism. Finally, the operation of a quaternary inverter configured with the double‐peak NDT device and a p‐channel transistor through Cadence circuit simulation is theoretically demonstrated. [ABSTRACT FROM AUTHOR]

One of the most attractive features of 2D WSe2 is a tunability in its electronic and optoelectronic properties depending on the layer number. To harness such unique characteristics for device applications, high quality and easily processable heterojunctions are required and relevant layer‐number‐dependent properties must be understood. Herein, a study is reported on hybrid heterojunctions between 2D WSe2 and organic molecules from one‐step solution chemistry and their layer‐number‐dependent properties. Eosin Y (EY) dye is selected as a p‐dopant and uniformly stacked on mechanically exfoliated WSe2 flakes via van der Waals interaction, forming a hybrid heterojunction with a type II alignment. The EY‐WSe2 heterojunction shows significantly enhanced currents compared to pristine WSe2 with a lower barrier height and a longer effective screening length. The work function of the heterostructure is also lower than that of pristine WSe2. The efficient exciton dissociation and doping effect by EY are confirmed by photocurrent and photoluminescence measurements, where WSe2 emission is markedly quenched by EY and exciton contribution decreases with layer number. These findings shed critical insights into layer‐number‐dependent electronic and optoelectronic properties of organic‐WSe2 layers and also provide simple yet effective means to construct transition metal dichalcogenide‐based heterostructures, which should be valuable for developing layered 2D devices. [ABSTRACT FROM AUTHOR]

Semiconductor p–n junctions are building blocks for optoelectronic devices. Recently, p–n junction devices based on 2D transition metal dichalcogenides (TMDCs) have been demonstrated in optoelectronic applications due to their thin thickness, flexibility, high carrier mobility, and high light‐absorption properties. To fabricate 2D semiconductor p–n junction devices, various methods are demonstrated, such as heterojunction structures, chemical doping, and electrostatic doping. In this work, lateral both p–n and n–p junctions in WSe2 devices, electrically controlled by using only a single‐gate electrode, are first reported. It is demonstrated that the single‐gated WSe2 p–n and n–p diodes form an internal built‐in electrical field, showing strong diode‐like current rectifying behavior and photovoltaic effect under the illumination. The resultant device exhibits a high current rectification ratio up to ≈106 and a power conversion efficiency of 0.1% under AM 1.5 illumination. A logical inverter based on the lateral and in‐plane contacted WSe2 device with a hexagonal boron nitride (h‐BN) gate dielectric is also presented. The electrode architecture engineering based on a single TMDC will be useful for applications that are more complicated such as p–n junction optoelectronic devices and inverters. [ABSTRACT FROM AUTHOR]

The control of electrical and optical characteristics of 2D transition‐metal dichalcogenides (TMDCs) through charge doping is essential to optimize the performances of optoelectronic devices based on TMDCs. In this study, a few‐layer tungsten diselenide (WSe2) is hybridized with organic gold(III)‐tetraphenylporphyrin (Au‐TPP) using a simple drop‐casting method. Nanoscale optical characteristics, measured by laser confocal microscopy, reveal that the photoluminescence intensity and exciton lifetime of Au‐TPP decrease after the hybridization with WSe2, which suggests the charge transfer from Au‐TPP to WSe2. For optoelectronic applications, photoresponsive field‐effect transistors (FETs) based on pristine WSe2 and WSe2/Au‐TPP hybrids are fabricated and compared. After the hybridization with Au‐TPP, the charge transport characteristics of the WSe2‐based FETs change to severe n‐type characteristics including a negative shift of the threshold voltage and increase in electron mobility. Significantly enhanced photoresponsivities (up to 310 times) are observed for the WSe2/Au‐TPP‐based FETs owing to their efficient light absorption and charge transfer from Au‐TPP to WSe2. Field‐effect transistors using WSe2/gold(III)‐tetraphenylporphyrin (Au‐TPP) hybrids demonstrate a change in electrical behavior from weak ambipolar to strong n‐type and a tremendous increase in photoresponsivity, which depends on the concentration of Au‐TPP. The photoluminescence quenching and the decrease of exciton lifetime of Au‐TPP after hybridization with WSe2 indicate charge transfer from Au‐TPP to WSe2. [ABSTRACT FROM AUTHOR]

The residue of common photo‐ and electron‐beam resists, such as poly(methyl methacrylate) (PMMA), is often present on the surface of 2D crystals after device fabrication. The residue degrades device properties by decreasing carrier mobility and creating unwanted doping. Here, MoS2 and WSe2 field effect transistors (FETs) with residue are cleaned by contact mode atomic force microscopy (AFM) and the impact of the residue on: 1) the intrinsic electrical properties, and 2) the effectiveness of electric double layer (EDL) gating are measured. After cleaning, AFM measurements confirm that the surface roughness decreases to its intrinsic state (i.e., ≈0.23 nm for exfoliated MoS2 and WSe2) and Raman spectroscopy shows that the characteristic peak intensities (E2g and A1g) increase. PMMA residue causes p‐type doping corresponding to a charge density of ≈7 × 1011 cm−2 on back‐gated MoS2 and WSe2 FETs. For FETs gated with polyethylene oxide (PEO)76:CsClO4, removing the residue increases the charge density by 4.5 × 1012 cm−2, and the maximum drain current by 247% (statistically significant, p < 0.05). Removing the residue likely allows the ions to be positioned closer to the channel surface, which is essential for achieving the best possible electrostatic gate control in ion‐gated devices. The impact of post‐lithography polymer residue on MoS2 and WSe2 is investigated on back‐gated and ionic‐gated field effect transistors. The removal of the residue is achieved by contact‐mode AFM without degrading the electronic properties, which increases charge density for back‐gated devices and enhances the gate coupling in ionic‐gated devices by increasing the proximity of ions to the 2D surface. [ABSTRACT FROM AUTHOR]

van der Waals (vdW) heterojunctions enable arbitrary combinations of different layered semiconductors with unique band structures, offering distinctive band engineering for photonic and optoelectronic devices with new functionalities and superior performance. Here, an interlayer photoresponse of a few‐layer MoSe2/WSe2 vdW heterojunction is reported. With proper electrical gating and bias, the heterojunction exhibits high‐sensitivity photodetection with the operation wavelength extended up to the telecommunication band (i.e. 1550 nm). The photoresponsivity and normalized photocurrent‐to‐dark current ratio reach up to 127 mA W−1 and 1.9 × 104 mW−1, respectively. The results not only provide a promising solution to realize high‐performance vdW telecommunication band photodetectors, but also pave the way for using sub‐bandgap engineering of two‐dimensional layered materials for photonic and optoelectronic applications. van der Waals heterostructures are demonstrated as building blocks for photonics and optoelectronics. Herein, a sub‐bandgap photodetection at λ = 1550 nm based on a MoSe2/WSe2 heterojunction is demonstrated. The high responsivity as well as high normalized photocurrent‐to‐dark current ratio indicate that the heterojunction device has promising applications in future optoelectronic. [ABSTRACT FROM AUTHOR]

Due to the development of 2D material transistors research and preparation process, many fundamental logic units, like inverter and NAND gate, have been achieved to promote large‐scale integration. However, there are critical challenges like voltage loss and large dynamic power consumption for integrated circuits based on 2D semiconductors. Here high‐performance logic devices via different MoS2‐WSe2 configurations, a MoS2‐WSe2 complementary logic transmission gate with the ability to transport electrical level without any voltage loss and a MoS2‐WSe2 complementary logic inverter with small dynamic power consumption and maximum voltage gain of 18 are demonstrated. Furthermore, an essential logic unit like Schmidt flip‐flop is put forward by combining MoS2‐WSe2 inverter and graphene floating gate. The realization of various logics achieved by different MoS2‐WSe2 configurations makes it much easier to fabricate multifunctional system on a chip, which has a significant meaning for the development of high density integrated circuits. Different complementary logic via configurable MoS2/WSe2 gate is demonstrated here, a MoS2‐WSe2 transmission gate with the ability to transport electrical level without any voltage loss and a MoS2‐WSe2 inverter with small dynamic power consumption. And on this basis, a new logic unit like the Schmidt flip‐flop is put forward, which can be applied to waveform transformation and pulse shaping. [ABSTRACT FROM AUTHOR]

Pulsed laser deposition (PLD) which is thickness‐adjustable deposition technique enables the fabrication of highly uniform monolayer and few‐layer WSe2 thin film on a large‐scale substrate, and these advances practical applicability of 2D material in the various field such as field effect transistor (FET) devices. More details can be found in article number 1800524 by Sehun Seo, Hojoong Choi, Sanghan Lee, and co‐workers. [ABSTRACT FROM AUTHOR]