Xingxing Zhang

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11 Nov 11:29

[ASAP] Chemiresistive Hydrogen Sensors: Fundamentals, Recent Advances, and Challenges

by Won-Tae Koo, Hee-Jin Cho, Dong-Ha Kim, Yoon Hwa Kim, Hamin Shin, Reginald M. Penner, and Il-Doo Kim

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ACS Nano
DOI: 10.1021/acsnano.0c05307
11 Nov 11:18

[ASAP] Exciton-Enabled Meta-Optics in Two-Dimensional Transition Metal Dichalcogenides

by Zeng Wang, Guanghui Yuan, Ming Yang, Jianwei Chai, Qing Yang Steve Wu, Tao Wang, Matej Sebek, Dan Wang||, Lei Wang||, Shijie Wang, Dongzhi Chi, Giorgio Adamo, Cesare Soci, Handong Sun□, Kun Huang, and Jinghua Teng

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Nano Letters
DOI: 10.1021/acs.nanolett.0c02712
02 Nov 01:54

Defect‐Rich Adhesive Molybdenum Disulfide/rGO Vertical Heterostructures with Enhanced Nanozyme Activity for Smart Bacterial Killing Application

by Longwei Wang, Fene Gao, Aizhu Wang, Xuanyu Chen, Hao Li, Xiao Zhang, Hong Zheng, Rui Ji, Bo Li, Xin Yu, Jing Liu, Zhanjun Gu, Fulin Chen, Chunying Chen
Defect‐Rich Adhesive Molybdenum Disulfide/rGO Vertical Heterostructures with Enhanced Nanozyme Activity for Smart Bacterial Killing Application

Molybdenum disulfide/rGO vertical heterostructures are demonstrated to possess triple enzyme‐like activities, which are further enhanced through light irradiation. Coupled with the rough surface that contributes excellent capacity for bacterial capture, preeminent antibacterial efficacy against drug‐resistant bacteria is exhibited both in vitro and in vivo by such a defect‐rich adhesive nanozyme, which will blaze a new path for the development of alternative antibiotics.


Abstract

Nanomaterials with intrinsic enzyme‐like activities, namely “nanozymes,” are showing increasing potential as a new type of broad‐spectrum antibiotics. However, their feasibility is still far from satisfactory, due to their low catalytic activity, poor bacterial capturing capacity, and complicated material design. Herein, a facile synthesis of a defect‐rich adhesive molybdenum disulfide (MoS2)/rGO vertical heterostructure (VHS) through a one‐step microwave‐assisted hydrothermal method is reported. This simple, convenient but effective method for rapid material synthesis enables extremely uniform and well‐dispersed MoS2/rGO VHS with abundant S and Mo vacancies and rough surface, for a performance approaching the requirements of practical application. It is demonstrated experimentally and theoretically that the as‐prepared MoS2/rGO VHS possesses defect and irradiation dual‐enhanced triple enzyme‐like activities (oxidase, peroxidase, and catalase) for promoting free‐radical generation, owing to much more active edge sites exposure. Meanwhile, the VHS‐achieved rough surface exhibits excellent capacity for bacterial capture, with elevated reactive oxygen species (ROS) destruction through local topological interactions. As a result, optimized efficacy against drug‐resistant Gram‐negative and Gram‐positive bacteria can be explored by such defect‐rich adhesive nanozymes, demonstrating a simple but powerful way to engineered nanozymes for alternative antibiotics.

02 Nov 01:53

Controllable Magnetic Proximity Effect and Charge Transfer in 2D Semiconductor and Double‐Layered Perovskite Manganese Oxide van der Waals Heterostructure

by Yan Zhang, Keisuke Shinokita, Kenji Watanabe, Takashi Taniguchi, Masato Goto, Daisuke Kan, Yuichi Shimakawa, Yutaka Moritomo, Taishi Nishihara, Yuhei Miyauchi, Kazunari Matsuda
Controllable Magnetic Proximity Effect and Charge Transfer in 2D Semiconductor and Double‐Layered Perovskite Manganese Oxide van der Waals Heterostructure

A novel van der Waals heterostructure consisting of monolayer MoSe2, Mn oxide, and a buffer layer (h‐BN) demonstrates magnetic proximity and charge transfer effect for the excitonic states due to phase transition of Mn oxide from ferromagnetic metal to paramagnetic insulator. The controllable thickness of h‐BN reveals a characteristic length scale of several nanometers in magnetic proximity and charge transfer.


Abstract

Optically generated excitonic states (excitons and trions) in transition metal dichalcogenides are highly sensitive to the electronic and magnetic properties of the materials underneath. Modulation and control of the excitonic states in a novel van der Waals (vdW) heterostructure of monolayer MoSe2 on double‐layered perovskite Mn oxide ((La0.8Nd0.2)1.2Sr1.8Mn2O7) is demonstrated, wherein the Mn oxide transforms from a paramagnetic insulator to a ferromagnetic metal. A discontinuous change in the exciton photoluminescence intensity via dielectric screening is observed. Further, a relatively high trion intensity is discovered due to the charge transfer from metallic Mn oxide under the Curie temperature. Moreover, the vdW heterostructures with an ultrathin h‐BN spacer layer demonstrate enhanced valley splitting and polarization of excitonic states due to the proximity effect of the ferromagnetic spins of Mn oxide. The controllable h‐BN thickness in vdW heterostructures reveals a several‐nanometer‐long scale of charge transfer as well as a magnetic proximity effect. The vdW heterostructure allows modulation and control of the excitonic states via dielectric screening, charge carriers, and magnetic spins.

02 Nov 01:53

Promoted Photocharge Separation in 2D Lateral Epitaxial Heterostructure for Visible‐Light‐Driven CO2 Photoreduction

by Li Wang, Xue Zhao, Dongdong Lv, Chuangwei Liu, Weihong Lai, Chunyi Sun, Zhongmin Su, Xun Xu, Weichang Hao, Shi Xue Dou, Yi Du
Promoted Photocharge Separation in 2D Lateral Epitaxial Heterostructure for Visible‐Light‐Driven CO2 Photoreduction

A 2D lateral heterostructure is in situ fabricated. Benefiting from the strong chemical bonding at the heterointerface, a strong internal electric field is generated between two components of the heterostructure, which facilitates photoexcited charge separation and transfer kinetics, and results in improved solar‐energy conversion efficiency.


Abstract

Photocarrier recombination remains a big barrier for the improvement of solar energy conversion efficiency. For 2D materials, construction of heterostructures represents an efficient strategy to promote photoexcited carrier separation via an internal electric field at the heterointerface. However, due to the difficulty in seeking two components with suitable crystal lattice mismatch, most of the current 2D heterostructures are vertical heterostructures and the exploration of 2D lateral heterostructures is scarce and limited. Here, lateral epitaxial heterostructures of BiOCl @ Bi2O3 at the atomic level are fabricated via sonicating‐assisted etching of Cl in BiOCl. This unique lateral heterostructure expedites photoexcited charge separation and transportation through the internal electric field induced by chemical bonding at the lateral interface. As a result, the lateral BiOCl @ Bi2O3 heterostructure demonstrates superior CO2 photoreduction properties with a CO yield rate of about 30 µmol g−1 h−1 under visible light illumination. The strategy to fabricate lateral epitaxial heterostructures in this work is expected to provide inspiration for preparing other 2D lateral heterostructures used in optoelectronic devices, energy conversion, and storage fields.

12 Oct 14:42

Record‐Low Subthreshold‐Swing Negative‐Capacitance 2D Field‐Effect Transistors

by Yang Wang, Xiaoyuan Bai, Junwei Chu, Hongbo Wang, Gaofeng Rao, Xinqiang Pan, Xinchuan Du, Kai Hu, Xuepeng Wang, Chuanhui Gong, Chujun Yin, Chao Yang, Chaoyi Yan, Chunyang Wu, Yao Shuai, Xianfu Wang, Min Liao, Jie Xiong
Record‐Low Subthreshold‐Swing Negative‐Capacitance 2D Field‐Effect Transistors

A 2D MoS2 negative‐capacitance field‐effect transistor based on a ferroelectric LiNbO3 platform performs a record‐low subthreshold swing of 4.97 mV dec−1 and quasi‐free hysteresis at room temperature, which can be attributed to the excellent capacitance matching under modulation of V ds, V g, and channel length.


Abstract

Power consumption is one of the most challenging bottlenecks for complementary metal‐oxide–semiconductor integration. Negative‐capacitance field‐effect transistors (NC‐FETs) offer a promising platform to break the thermionic limit defined by the Boltzmann tyranny and architect energy‐efficient devices. However, it is a great challenge to achieving ultralow‐subthreshold‐swing (SS) (10 mV dec−1) and small‐hysteresis NC‐FETs simultaneously at room temperature, which has only been reported using the hafnium zirconium oxide system. Here, based on a ferroelectric LiNbO3 thin film with great spontaneous polarization, an ultralow‐SS NC‐FET with small hysteresis is designed. The LiNbO3 NC‐FET platform exhibits a record‐low SS of 4.97 mV dec−1 with great repeatability due to the superior capacitance matching characteristic as evidenced by the negative differential resistance phenomenon. By modulating the structure and operating parameters (such as channel length (L ch), drain–sourse bias (V ds), and gate bias (V g)) of devices, an optimized SS from ≈40 to ≈10 mV dec−1 and hysteresis from ≈900 to ≈60 mV are achieved simultaneously. The results provide a new potential method for future highly integrated electronic and optical integrated energy‐efficient devices.

09 Oct 02:24

[ASAP] Neutral Exciton Diffusion in Monolayer MoS2

by Shiekh Zia Uddin, Hyungjin Kim, Monica Lorenzon, Matthew Yeh, Der-Hsien Lien, Edward S. Barnard, Han Htoon, Alexander Weber-Bargioni, and Ali Javey

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ACS Nano
DOI: 10.1021/acsnano.0c05305
09 Oct 02:22

[ASAP] Oxide-Free Three-Dimensional Germanium/Silicon Core–Shell Metalattice Made by High-Pressure Confined Chemical Vapor Deposition

by Pratibha Mahale, Parivash Moradifar, Hiu Yan Cheng, Nabila Nabi Nova, Alex J. Grede, Byeongdu Lee, Luis R. De Jesús, Maxwell Wetherington, Noel C. Giebink, John V. Badding, Nasim Alem, and Thomas E. Mallouk

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ACS Nano
DOI: 10.1021/acsnano.0c03559
09 Oct 02:20

[ASAP] Uncovering the Effects of Metal Contacts on Monolayer MoS2

by Kirstin Schauble, Dante Zakhidov, Eilam Yalon, Sanchit Deshmukh, Ryan W. Grady, Kayla A. Cooley, Connor J. McClellan, Sam Vaziri, Donata Passarello, Suzanne E. Mohney, Michael F. Toney, A. K. Sood, Alberto Salleo, and Eric Pop□

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ACS Nano
DOI: 10.1021/acsnano.0c03515
09 Oct 02:20

[ASAP] van der Waals Epitaxy of Soft Twisted Bilayers: Lattice Relaxation and Mass Density Waves

by Cong Jin, Brian C. Olsen, Erik J. Luber, and Jillian M. Buriak

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ACS Nano
DOI: 10.1021/acsnano.0c05310
09 Oct 02:18

[ASAP] Integrated Wafer Scale Growth of Single Crystal Metal Films and High Quality Graphene

by Oliver J. Burton, Fabien C-P. Massabuau, Vlad-Petru Veigang-Radulescu, Barry Brennan, Andrew J. Pollard, and Stephan Hofmann

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ACS Nano
DOI: 10.1021/acsnano.0c05685
09 Oct 02:18

[ASAP] Trion-Mediated Förster Resonance Energy Transfer and Optical Gating Effect in WS2/hBN/MoSe2 Heterojunction

by Zehua Hu, Pedro Ludwig Hernández-Martínez, Xue Liu, Mohamed-Raouf Amara, Weijie Zhao, Kenji Watanabe, Takashi Taniguchi+, Hilmi Volkan Demir, and Qihua Xiong

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ACS Nano
DOI: 10.1021/acsnano.0c05447
09 Oct 02:17

[ASAP] Fast Organic Vapor Phase Deposition of Thin Films in Light-Emitting Diodes

by Boning Qu, Kan Ding, Kai Sun, Shaocong Hou, Steven Morris, Max Shtein, and Stephen R. Forrest

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ACS Nano
DOI: 10.1021/acsnano.0c07017
09 Oct 02:13

[ASAP] Photocurrent Imaging of Multi-Memristive Charge Density Wave Switching in Two-Dimensional 1T-TaS2

by Tarun Patel, Junichi Okamoto, Tina Dekker, Bowen Yang, Jingjing Gao, Xuan Luo, Wenjian Lu, Yuping Sun, and Adam W. Tsen

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Nano Letters
DOI: 10.1021/acs.nanolett.0c02537
09 Oct 02:12

[ASAP] Manipulation of the van der Waals Magnet Cr2Ge2Te6 by Spin–Orbit Torques

by Vishakha Gupta, Thow Min Cham, Gregory M. Stiehl, Arnab Bose, Joseph A. Mittelstaedt, Kaifei Kang, Shengwei Jiang, Kin Fai Mak, Jie Shan, Robert A. Buhrman, and Daniel C. Ralph

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Nano Letters
DOI: 10.1021/acs.nanolett.0c02965
09 Oct 02:11

[ASAP] Heteromoiré Engineering on Magnetic Bloch Transport in Twisted Graphene Superlattices

by Fanrong Lin, Jiabin Qiao, Junye Huang, Jiawei Liu, Deyi Fu, Alexander S. Mayorov, Hao Chen, Paromita Mukherjee, Tingyu Qu, Chorng-Haur Sow, Kenji Watanabe, Takashi Taniguchi, and Barbaros Özyilmaz

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Nano Letters
DOI: 10.1021/acs.nanolett.0c03062
09 Oct 02:11

[ASAP] Pnictogens Allotropy and Phase Transformation during van der Waals Growth

by Matthieu Fortin-Deschênes, Hannes Zschiesche, Tevfik O. Menteş, Andrea Locatelli, Robert M. Jacobberger, Francesca Genuzio, Maureen J. Lagos, Deepnarayan Biswas, Chris Jozwiak, Jill A. Miwa, Sren Ulstrup, Aaron Bostwick, Eli Rotenberg, Michael S. Arnold, Gianluigi A. Botton, and Oussama Moutanabbir

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Nano Letters
DOI: 10.1021/acs.nanolett.0c03372
09 Oct 02:10

[ASAP] Thermomechanical Nanostraining of Two-Dimensional Materials

by Xia Liu, Amit Kumar Sachan, Samuel Tobias Howell, Ana Conde-Rubio, Armin W. Knoll, Giovanni Boero, Renato Zenobi, and Jürgen Brugger

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Nano Letters
DOI: 10.1021/acs.nanolett.0c03358
09 Oct 02:02

Diode‐Like Selective Enhancement of Carrier Transport through Metal–Semiconductor Interface Decorated by Monolayer Boron Nitride

by Hemendra Nath Jaiswal, Maomao Liu, Simran Shahi, Sichen Wei, Jihea Lee, Anindita Chakravarty, Yutong Guo, Ruiqiang Wang, Jung Mu Lee, Chaoran Chang, Yu Fu, Ripudaman Dixit, Xiaochi Liu, Cheng Yang, Fei Yao, Huamin Li
Diode‐Like Selective Enhancement of Carrier Transport through Metal–Semiconductor Interface Decorated by Monolayer Boron Nitride

A novel diode‐like selective enhancement of the carrier transport through a metal–insulator–semiconductor (MIS) contact is revealed through comparison with a conventional metal–semiconductor contact on a single monolayer MoS2 triangular domain. The MIS contact exploits monolayer hexagonal boron nitride as an ultrathin decorating layer added between MoS2 and the metal contact.


Abstract

2D semiconductors such as monolayer molybdenum disulfide (MoS2) are promising material candidates for next‐generation nanoelectronics. However, there are fundamental challenges related to their metal–semiconductor (MS) contacts, which limit the performance potential for practical device applications. In this work, 2D monolayer hexagonal boron nitride (h‐BN) is exploited as an ultrathin decorating layer to form a metal–insulator–semiconductor (MIS) contact, and an innovative device architecture is designed as a platform to reveal a novel diode‐like selective enhancement of the carrier transport through the MIS contact. The contact resistance is significantly reduced when the electrons are transported from the semiconductor to the metal, but is barely affected when the electrons are transported oppositely. A concept of carrier collection barrier is proposed to interpret this intriguing phenomenon as well as a negative Schottky barrier height obtained from temperature‐dependent measurements, and the critical role of the collection barrier at the drain end is shown for the overall transistor performance.

09 Oct 02:00

Multioperation‐Mode Light‐Emitting Field‐Effect Transistors Based on van der Waals Heterostructure

by Junyoung Kwon, June‐Chul Shin, Huije Ryu, Jae Yoon Lee, Dongjea Seo, Kenji Watanabe, Takashi Taniguchi, Young Duck Kim, James Hone, Chul‐Ho Lee, Gwan‐Hyoung Lee
Multioperation‐Mode Light‐Emitting Field‐Effect Transistors Based on van der Waals Heterostructure

A light emitting transistor based on van der Waals heterostructure is demonstrated. Utilizing tunable graphene contacts, holes and electrons are separately injected into the ambipolar WSe2 monolayer. By balanced recombination of electrons and holes, the external quantum efficiency reaches ≈6% at room temperature. Multimode operation of this device powered by combination of electrical and optical states would be beneficial for optical circuitry.


Abstract

2D semiconductors have shown great potential for application to electrically tunable optoelectronics. Despite the strong excitonic photoluminescence (PL) of monolayer transition metal dichalcogenides (TMDs), their efficient electroluminescence (EL) has not been achieved due to the low efficiency of charge injection and electron–hole recombination. Here, multioperation‐mode light‐emitting field‐effect transistors (LEFETs) consisting of a monolayer WSe2 channel and graphene contacts coupled with two top gates for selective and balanced injection of charge carriers are demonstrated. Visibly observable EL is achieved with the high external quantum efficiency of ≈6% at room temperature due to efficient recombination of injected electrons and holes in a confined 2D channel. Further, electrical tunability of both the channel and contacts enables multioperation modes, such as antiambipolar, depletion,and unipolar regions, which can be utilized for polarity‐tunable field‐effect transistors and photodetectors. The work exhibits great potential for use in 2D semiconductor LEFETs for novel optoelectronics capable of high efficiency, multifunctions, and heterointegration.

09 Oct 01:58

Strain‐Sensitive Magnetization Reversal of a van der Waals Magnet

by Yu Wang, Cong Wang, Shi‐Jun Liang, Zecheng Ma, Kang Xu, Xiaowei Liu, Lili Zhang, Alemayehu S. Admasu, Sang‐Wook Cheong, Lizheng Wang, Moyu Chen, Zenglin Liu, Bin Cheng, Wei Ji, Feng Miao
Strain‐Sensitive Magnetization Reversal of a van der Waals Magnet

An ultrasensitive magnetization reversal in the van der Waals magnet Fe3GeTe2 is realized by strain. Remarkably increased coercive field, Curie temperature, and transition temperature between single‐ and labyrinthine‐domain states under tensile strain are also observed. The strain‐tunable magnetism could result from the sensitive change of magnetic anisotropy energy with the theoretical results.


Abstract

By virtue of the layered structure, van der Waals (vdW) magnets are sensitive to the lattice deformation controlled by the external strain, providing an ideal platform to explore the one‐step magnetization reversal that is still conceptual in conventional magnets due to the limited strain‐tuning range of the coercive field. In this study, a uniaxial tensile strain is applied to thin flakes of the vdW magnet Fe3GeTe2 (FGT), and a dramatic increase of the coercive field (H c) by more than 150% with an applied strain of 0.32% is observed. Moreover, the change of the transition temperatures between the different magnetic phases under strain is investigated, and the phase diagram of FGT in the strain–temperature plane is obtained. Comparing the phase diagram with theoretical results, the strain‐tunable magnetism is attributed to the sensitive change of magnetic anisotropy energy. Remarkably, strain allows an ultrasensitive magnetization reversal to be achieved, which may promote the development of novel straintronic device applications.

09 Oct 01:57

Spin‐Orbit Torque Magnetization Switching in MoTe2/Permalloy Heterostructures

by Shiheng Liang, Shuyuan Shi, Chuang‐Han Hsu, Kaiming Cai, Yi Wang, Pan He, Yang Wu, Vitor M. Pereira, Hyunsoo Yang
Spin‐Orbit Torque Magnetization Switching in MoTe2/Permalloy Heterostructures

Realizing efficient spin‐orbit‐based switching requires the harnessing of both new materials and physics to obtain high charge‐to‐spin conversion efficiencies. The observation of spin‐orbit torque switching in bilayers consisting of a semimetallic film of 1T′‐MoTe2 adjacent to permalloy is reported. Deterministic switching is achieved without external magnetic fields at room temperature with currents one order of magnitude smaller than those using heavy metals.


Abstract

The ability to switch magnetic elements by spin‐orbit‐induced torques has recently attracted much attention for a path toward high‐performance, nonvolatile memories with low power consumption. Realizing efficient spin‐orbit‐based switching requires the harnessing of both new materials and novel physics to obtain high charge‐to‐spin conversion efficiencies, thus making the choice of spin source crucial. Here, the observation of spin‐orbit torque switching in bilayers consisting of a semimetallic film of 1T′‐MoTe2 adjacent to permalloy is reported. Deterministic switching is achieved without external magnetic fields at room temperature, and the switching occurs with currents one order of magnitude smaller than those typical in devices using the best‐performing heavy metals. The thickness‐dependence can be understood if the interfacial spin‐orbit contribution is considered in addition to the bulk spin Hall effect. Further threefold reduction in the switching current is demonstrated with resort to dumbbell‐shaped magnetic elements. These findings foretell exciting prospects of using MoTe2 for low‐power semimetal‐material‐based spin devices.

09 Oct 01:53

High‐Throughput Growth of Wafer‐Scale Monolayer Transition Metal Dichalcogenide via Vertical Ostwald Ripening

by Minsu Seol, Min‐Hyun Lee, Haeryong Kim, Keun Wook Shin, Yeonchoo Cho, Insu Jeon, Myoungho Jeong, Hyung‐Ik Lee, Jiwoong Park, Hyeon‐Jin Shin
High‐Throughput Growth of Wafer‐Scale Monolayer Transition Metal Dichalcogenide via Vertical Ostwald Ripening

High‐throughput growth of monolayer transition metal dichalcogenides (TMDs) is developed on 6‐inch wafer scale. Periodically interrupting the precursor supply drives lateral growth via the surface diffusion of adatoms on the pre‐synthesized TMDs (vertical Ostwald ripening). The as‐grown TMD possesses high crystallinity with well‐stitched grains, and uniform electrical properties even after transfer by an etching‐free de‐bonding and bonding process.


Abstract

For practical device applications, monolayer transition metal dichalcogenide (TMD) films must meet key industry needs for batch processing, including the high‐throughput, large‐scale production of high‐quality, spatially uniform materials, and reliable integration into devices. Here, high‐throughput growth, completed in 12 min, of 6‐inch wafer‐scale monolayer MoS2 and WS2 is reported, which is directly compatible with scalable batch processing and device integration. Specifically, a pulsed metal–organic chemical vapor deposition process is developed, where periodic interruption of the precursor supply drives vertical Ostwald ripening, which prevents secondary nucleation despite high precursor concentrations. The as‐grown TMD films show excellent spatial homogeneity and well‐stitched grain boundaries, enabling facile transfer to various target substrates without degradation. Using these films, batch fabrication of high‐performance field‐effect transistor (FET) arrays in wafer‐scale is demonstrated, and the FETs show remarkable uniformity. The high‐throughput production and wafer‐scale automatable transfer will facilitate the integration of TMDs into Si‐complementary metal‐oxide‐semiconductor platforms.

09 Oct 01:48

Evaporated SexTe1‐x Thin Films with Tunable Bandgaps for Short‐Wave Infrared Photodetectors

by Chaoliang Tan, Matin Amani, Chunsong Zhao, Mark Hettick, Xiaohui Song, Der‐Hsien Lien, Hao Li, Matthew Yeh, Vivek Raj Shrestha, Kenneth B. Crozier, Mary C. Scott, Ali Javey
Evaporated SexTe1‐x Thin Films with Tunable Bandgaps for Short‐Wave Infrared Photodetectors

Thermally evaporated Se x Te1‐ x alloy thin films with tunable bandgaps (from 0.31 eV to 1.87 eV) are prepared for the fabrication of high‐performance short‐wave infrared photodetectors. The Se0.32Te0.68‐film‐based photoconductor fabricated on an optical cavity substrate exhibits a cut‐off wavelength at ≈1.7 μm and gives a responsivity of 1.5 AW−1 and implied detectivity of 6.5 × 1010 cm Hz1/2 W−1 at 1.55 μm at room temperature.


Abstract

Semiconducting absorbers in high‐performance short‐wave infrared (SWIR) photodetectors and imaging sensor arrays are dominated by single‐crystalline germanium and III–V semiconductors. However, these materials require complex growth and device fabrication procedures. Here, thermally evaporated Se x Te1‐ x alloy thin films with tunable bandgaps for the fabrication of high‐performance SWIR photodetectors are reported. From absorption measurements, it is shown that the bandgaps of Se x Te1‐ x films can be tuned continuously from 0.31 eV (Te) to 1.87 eV (Se). Owing to their tunable bandgaps, the peak responsivity position and photoresponse edge of Se x Te1‐ x film‐based photoconductors can be tuned in the SWIR regime. By using an optical cavity substrate consisting of Au/Al2O3 to enhance its absorption near the bandgap edge, the Se0.32Te0.68 film (an optical bandgap of ≈0.8 eV)‐based photoconductor exhibits a cut‐off wavelength at ≈1.7 μm and gives a responsivity of 1.5 AW−1 and implied detectivity of 6.5 × 1010 cm Hz1/2 W−1 at 1.55 μm at room temperature. Importantly, the nature of the thermal evaporation process enables the fabrication of Se0.32Te0.68‐based 42 × 42 focal plane arrays with good pixel uniformity, demonstrating the potential of this unique material system used for infrared imaging sensor systems.

09 Oct 01:43

Liquid‐Metal Synthesized Ultrathin SnS Layers for High‐Performance Broadband Photodetectors

by Vaishnavi Krishnamurthi, Hareem Khan, Taimur Ahmed, Ali Zavabeti, Sherif Abdulkader Tawfik, Shubhendra Kumar Jain, Michelle J. S. Spencer, Sivacarendran Balendhran, Kenneth B Crozier, Ziyuan Li, Lan Fu, Md Mohiuddin, Mei Xian Low, Babar Shabbir, Andreas Boes, Arnan Mitchell, Christopher F. McConville, Yongxiang Li, Kourosh Kalantar‐Zadeh, Nasir Mahmood, Sumeet Walia
Liquid‐Metal Synthesized Ultrathin SnS Layers for High‐Performance Broadband Photodetectors

Miniaturized photodetectors are key for the next generation of sensing, communication, and imaging technologies. Single‐atom‐thick SnS layers are printed on a millimeter scale to showcase application in high‐performance photodetectors. These SnS‐based ultrafast photodetectors show a broadband spectral response ranging from deep ultraviolet to near infrared wavelengths (i.e., 280 to 850 nm) with excellent figures of merit.


Abstract

Atomically thin materials face an ongoing challenge of scalability, hampering practical deployment despite their fascinating properties. Tin monosulfide (SnS), a low‐cost, naturally abundant layered material with a tunable bandgap, displays properties of superior carrier mobility and large absorption coefficient at atomic thicknesses, making it attractive for electronics and optoelectronics. However, the lack of successful synthesis techniques to prepare large‐area and stoichiometric atomically thin SnS layers (mainly due to the strong interlayer interactions) has prevented exploration of these properties for versatile applications. Here, SnS layers are printed with thicknesses varying from a single unit cell (0.8 nm) to multiple stacked unit cells (≈1.8 nm) synthesized from metallic liquid tin, with lateral dimensions on the millimeter scale. It is reveal that these large‐area SnS layers exhibit a broadband spectral response ranging from deep‐ultraviolet (UV) to near‐infrared (NIR) wavelengths (i.e., 280–850 nm) with fast photodetection capabilities. For single‐unit‐cell‐thick layered SnS, the photodetectors show upto three orders of magnitude higher responsivity (927 A W−1) than commercial photodetectors at a room‐temperature operating wavelength of 660 nm. This study opens a new pathway to synthesize reproduceable nanosheets of large lateral sizes for broadband, high‐performance photodetectors. It also provides important technological implications for scalable applications in integrated optoelectronic circuits, sensing, and biomedical imaging.

09 Oct 01:40

Air‐Stable Low‐Symmetry Narrow‐Bandgap 2D Sulfide Niobium for Polarization Photodetection

by Yang Wang, Peisong Wu, Zhen Wang, Man Luo, Fang Zhong, Xun Ge, Kun Zhang, Meng Peng, Yan Ye, Qing Li, Haonan Ge, Jiafu Ye, Ting He, Yunfeng Chen, Tengfei Xu, Chenhui Yu, Yueming Wang, Zhigao Hu, Xiaohao Zhou, Chongxin Shan, Mingsheng Long, Peng Wang, Peng Zhou, Weida Hu
Air‐Stable Low‐Symmetry Narrow‐Bandgap 2D Sulfide Niobium for Polarization Photodetection

Novel 2D anisotropic sulfide niobium (NbS3) is introduced into the material family by demonstrating its in‐plane structure, phonon vibrations, and electrical and optical anisotropies. Meaningfully, NbS3 Schottky photodetectors exhibit broadband detection sensitivity (400–10 600 nm), excellent response time (as fast as 11 µs), photoelectrical dichroic ratio (1.84), and high‐quality polarization imaging.


Abstract

Low‐symmetry 2D materials with unique anisotropic optical and optoelectronic characteristics have attracted a lot of interest in fundamental research and manufacturing of novel optoelectronic devices. Exploring new and low‐symmetry narrow‐bandgap 2D materials will be rewarding for the development of nanoelectronics and nano‐optoelectronics. Herein, sulfide niobium (NbS3), a novel transition metal trichalcogenide semiconductor with low‐symmetry structure, is introduced into a narrowband 2D material with strong anisotropic physical properties both experimentally and theoretically. The indirect bandgap of NbS3 with highly anisotropic band structures slowly decreases from 0.42 eV (monolayer) to 0.26 eV (bulk). Moreover, NbS3 Schottky photodetectors have excellent photoelectric performance, which enables fast photoresponse (11.6 µs), low specific noise current (4.6 × 10−25 A2 Hz−1), photoelectrical dichroic ratio (1.84) and high‐quality reflective polarization imaging (637 nm and 830 nm). A room‐temperature specific detectivity exceeding 107 Jones can be obtained at the wavelength of 3 µm. These excellent unique characteristics will make low‐symmetry narrow‐bandgap 2D materials become highly competitive candidates for future anisotropic optical investigations and mid‐infrared optoelectronic applications.

09 Oct 01:39

Supramolecular Two‐Dimensional Systems and Their Biological Applications

by Taeyeon Kim, Jung Yeon Park, Jiwon Hwang, Gunhee Seo, Yongju Kim
Supramolecular Two‐Dimensional Systems and Their Biological Applications

Cell membranes are 2D structures in biological systems and have various characteristics such as large surface area, flexibility, and molecule recognition ability. Supramolecular 2D materials inspired from biological systems can serve as the next generation of biofunctional materials. The current advances in 2D material development by the molecular assembly of aromatic amphiphiles and its biological applications are discussed.


Abstract

Various biological systems rely on the supramolecular assembly of biomolecules through noncovalent bonds for performing sophisticated functions. In particular, cell membranes, which are 2D structures in biological systems, have various characteristics such as a large surface, flexibility, and molecule‐recognition ability. Supramolecular 2D materials based on biological systems provide a novel perspective for the development of functional 2D materials. The physical and chemical properties of 2D structures, attributed to their large surface area, can enhance the sensitivity of the detection of target molecules, molecular loading, and bioconjugation efficiency, suggesting the potential utility of functional 2D materials as candidates for biological systems. Although several types of studies on supramolecular 2D materials have been reported, supramolecular biofunctional 2D materials have not been reviewed previously. In this regard, the current advances in 2D material development using molecular assembly are discussed with respect to the rational design of self‐assembling aromatic amphiphiles, the formation of 2D structures, and the biological applications of functional 2D materials.

09 Oct 01:38

Visualizing the Anomalous Charge Density Wave States in Graphene/NbSe2 Heterostructures

by Yu Chen, Lishu Wu, Hai Xu, Chunxiao Cong, Si Li, Shun Feng, Hongbo Zhang, Chenji Zou, Jingzhi Shang, Shengyuan A. Yang, Kian Ping Loh, Wei Huang, Ting Yu
Visualizing the Anomalous Charge Density Wave States in Graphene/NbSe2 Heterostructures

Prominent suppression of the charge density wave (CDW) orders in graphene/NbSe2 heterostructures is observed by Raman spectroscopy and scanning tunneling microscopy/spectroscopy. The findings propose a new criterion to determine the T CDW through monitoring the line shape of the A1g mode. First‐principles calculations imply that interfacial electron doping suppresses the CDW states by impeding the lattice distortion of 2H‐NbSe2.


Abstract

Metallic layered transition metal dichalcogenides (TMDs) host collective many‐body interactions, including the competing superconducting and charge density wave (CDW) states. Graphene is widely employed as a heteroepitaxial substrate for the growth of TMD layers and as an ohmic contact, where the graphene/TMD heterostructure is naturally formed. The presence of graphene can unpredictably influence the CDW order in 2D CDW conductors. This work reports the CDW transitions of 2H‐NbSe2 layers in graphene/NbSe2 heterostructures. The evolution of Raman spectra demonstrates that the CDW phase transition temperatures (T CDW) of NbSe2 are dramatically decreased when capped by graphene. The induced anomalous short‐range CDW state is confirmed by scanning tunneling microscopy measurements. The findings propose a new criterion to determine the T CDW through monitoring the line shape of the A1g mode. Meanwhile, the 2D band is also discovered as an indicator to observe the CDW transitions. First‐principles calculations imply that interfacial electron doping suppresses the CDW states by impeding the lattice distortion of 2H‐NbSe2. The extraordinary random CDW lattice suggests deep insight into the formation mechanism of many collective electronic states and possesses great potential in modulating multifunctional devices.

09 Oct 01:37

Tunable Ferromagnetism and Thermally Induced Spin Flip in Vanadium‐Doped Tungsten Diselenide Monolayers at Room Temperature

by Yen Thi Hai Pham, Mingzu Liu, Valery Ortiz Jimenez, Zhuohang Yu, Vijaysankar Kalappattil, Fu Zhang, Ke Wang, Teague Williams, Mauricio Terrones, Manh‐Huong Phan
Tunable Ferromagnetism and Thermally Induced Spin Flip in Vanadium‐Doped Tungsten Diselenide Monolayers at Room Temperature

Strong and tunable room‐temperature ferromagnetism is achieved in vanadium‐doped tungsten diselenide monolayers using a reproducible and atmospheric‐pressure film sulfidation growth method. As the vanadium concentration increases, the saturation magnetization increases, which is optimal at ≈4 at% vanadium—the highest doping level ever achieved for V‐doped WSe2 monolayers. A novel thermally induced spin flipping effect is also discovered in these monolayers.


Abstract

The outstanding optoelectronic and valleytronic properties of transition metal dichalcogenides (TMDs) have triggered intense research efforts by the scientific community. An alternative to induce long‐range ferromagnetism (FM) in TMDs is by introducing magnetic dopants to form a dilute magnetic semiconductor. Enhancing ferromagnetism in these semiconductors not only represents a key step toward modern TMD‐based spintronics, but also enables exploration of new and exciting dimensionality‐driven magnetic phenomena. To this end, tunable ferromagnetism at room temperature and a thermally induced spin flip (TISF) in monolayers of V‐doped WSe2 are shown. As vanadium concentration increases, the saturation magnetization increases, which is optimal at ≈4 at% vanadium; the highest doping level ever achieved for V‐doped WSe2 monolayers. The TISF occurs at ≈175 K and becomes more pronounced upon increasing the temperature toward room temperature. The TISF can be manipulated by changing the vanadium concentration. The TISF is attributed to the magnetic‐field‐ and temperature‐dependent flipping of the nearest W‐site magnetic moments that are antiferromagnetically coupled to the V magnetic moments in the ground state. This is fully supported by a recent spin‐polarized density functional theory study. The findings pave the way for the development of novel spintronic and valleytronic nanodevices and stimulate further research.

09 Oct 01:32

Chemical doping of organic semiconductors for thermoelectric applications

Chem. Soc. Rev., 2020, 49,7210-7228
DOI: 10.1039/D0CS00204F, Tutorial Review
Wenrui Zhao, Jiamin Ding, Ye Zou, Chong-an Di, Daoben Zhu
This review highlights thermoelectric-oriented chemical doping of organic semiconductors from molecular design, doping mechanisms, doping methods and insightful strategies.
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