Search query: Intrinsic structural defects in monolayer molybdenum disulfide

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abstract: Monolayer molybdenum disulfide (MoS2) is a two dimensional direct band gap semiconductor with unique mechanical, electronic, optical, and chemical properties that can be utilized for novel nanoelectronics and optoelectronics devices. The performance of these devices strongly depends on the quality and defect morphology of the MoS2 layers. Here we provide a systematic study of intrinsic structural defects in chemical vapor phase grown monolayer MoS2, including point defects, dislocations, grain boundaries, and edges, via direct atomic resolution imaging, and explore their energy landscape and electronic properties using first principles calculations. A rich variety of point defects and dislocation cores, distinct from those present in graphene, were observed in MoS2. We discover that one dimensional metallic wires can be created via two different types of 60deg grain boundaries consisting of distinct 4 fold ring chains. A new type of edge reconstruction, representing a transition state during growth, was also identified, providing insights into the material growth mechanism. The atomic scale study of structural defects presented here brings new opportunities to tailor the properties of MoS2 via controlled synthesis and defect engineering.
author_names: Wu Zhou

Xiaolong Zou

Sina Najmaei

Zheng Liu

Yumeng Shi

Jing Kong

Jun Lou

Pulickel M Ajayan

Boris I Yakobson

Juan Carlos Idrobo
title: Intrinsic structural defects in monolayer molybdenum disulfide.
venue: Nano letters
year: 2013

abstract: Molybdenum disulfide is considered as one of the most promising two dimensional semiconductors for electronic and optoelectronic device applications. So far, the charge transport in monolayer molybdenum disulfide is dominated by extrinsic factors such as charged impurities, structural defects and traps, leading to much lower mobility than the intrinsic limit. Here we develop a facile low temperature thiol chemistry route to repair the sulfur vacancies and improve the interface, resulting in significant reduction of the charged impurities and traps. High mobility >80 cm(2) V( 1) s( 1) is achieved in backgated monolayer molybdenum disulfide field effect transistors at room temperature. Furthermore, we develop a theoretical model to quantitatively extract the key microscopic quantities that control the transistor performances, including the density of charged impurities, short range defects and traps. Our combined experimental and theoretical study provides a clear path towards intrinsic charge transport in two dimensional dichalcogenides for future high performance device applications.
author_names: Zhihao Yu

Yiming Pan

Yuting Shen

Zilu Wang

Zhun-Yong Ong

Tao Xu

Run Xin

Lijia Pan

Baigeng Wang

Litao Sun

Jinlan Wang

Gang Zhang

Yan Zhang

Yi Shi

Xinran Wang
title: Towards intrinsic charge transport in monolayer molybdenum disulfide by defect and interface engineering.
venue: Nature communications
year: 2014

abstract: It is revealed by recent experimental and theoretical nanoindentation studies that the low concentration of monovacancy produces an abnormal noticeable stiffening effect on graphene sheets, which depending on the defect type. As for graphene like quasi two dimensional (2D) nanomaterials, the single layer molybdenum disulfide (SLMoS2) has intrinsic structural defects that are distinct to graphene. Therefore, it is intriguing to investigate if any kind of defects will lead to such unique effect on the mechanical properties of SLMoS2, including the elasticity and strength. Following our preliminary studies on the VMoS3 point defect, herein, we perform molecular dynamics simulations to look into the effect of the low concentration of single molybdenum vacancy defects on the mechanical properties of SLMoS2, under uniaxial tensile tests. The defect fractions of the single Mo vacancy varying from 0.1% to 1.0% are considered in our works, together with the random and regular vacancy distributions. Single molybdenum vacancy defects are found, as common intuition would suggest, to reduce the mechanical properties of SLMoS2, including the elastic modulus and tensile strength. The effect of chirality on the mechanical properties of the SLMoS2 is also discussed in the present work.
author_names: Minglin Li

Yaling Wan

Weidong Wang
title: Prediction of mechanical properties for defective monolayer MoS2 with single molybdenum vacancy defects using molecular dynamics simulations
venue: 2017 IEEE 17th International Conference on Nanotechnology (IEEE NANO)
year: 2017

abstract: Structural defects in the molybdenum disulfide (MoS2) monolayer are widely known for strongly altering its properties. Therefore, a deep understanding of these structural defects and how they affect MoS2 electronic properties is of fundamental importance. Here, we report on the incorporation of atomic hydrogen in monolayered MoS2 to tune its structural defects. We demonstrate that the electronic properties of single layer MoS2 can be tuned from the intrinsic electron (n) to hole (p) doping via controlled exposure to atomic hydrogen at room temperature. Moreover, this hydrogenation process represents a viable technique to completely saturate the sulfur vacancies present in the MoS2 flakes. The successful incorporation of hydrogen in MoS2 leads to the modification of the electronic properties as evidenced by high resolution X ray photoemission spectroscopy and density functional theory calculations. Micro Raman spectroscopy and angle resolved photoemission spectroscopy measurements show the high quality of the hydrogenated MoS2 confirming the efficiency of our hydrogenation process. These results demonstrate that the MoS2 hydrogenation could be a significant and efficient way to achieve tunable doping of transition metal dichalcogenides (TMD) materials with non TMD elements.
author_names: Debora Pierucci

Hugo Henck

Zeineb Ben Aziza

Carl H Naylor

Adrian Balan

Julien E Rault

Mathieu G Silly

Yannick J Dappe

Francois Bertran

Patrick Le Fevre

Fausto Sirotti

A T Charlie Johnson

Abdelkarim Ouerghi
title: Tunable Doping in Hydrogenated Single Layered Molybdenum Disulfide.
venue: ACS nano
year: 2017

abstract: Nanoscale molybdenum disulfide (MoS2) has attracted ever growing interest as one of the most promising nonprecious catalysts for hydrogen evolution reaction (HER) However, the active sites of pristine MoS2 are located at the edges, leaving a large area of basal planes useless. Here, we systematically evaluate the capabilities of 16 kinds of structural defects including point defects (PDs) and grain boundaries (GBs) to activate the basal plane of MoS2 monolayer. Our first principle calculations show that six types of defects (i.e. Vs, VMoS3, MoS2 PDs; 4|8a, S bridge, and Mo Mo bond GBs) can greatly improve the HER performance of the in plane domains of MoS2. More importantly, Vs and MoS2 PDs and S bridge and 4|8a GBs exhibit outstanding activity in both Heyrovsky and Tafel reactions as well. Moreover, the different HER activities of defects are well understood by an amendatory band center model, which is applicable to a broad class of systems with localized defect states. Our study provides a comprehensi.
author_names: Yixin Ouyang

Chongyi Ling

Qian Chen

Zilu Wang

Li Shi

Jinlan Wang
title: Activating Inert Basal Planes of MoS2 for Hydrogen Evolution Reaction through the Formation of Different Intrinsic Defects
year: 2016

abstract: Pristine monocrystalline molybdenum disulfide (MoS2) possesses high mechanical strength comparable to that of stainless steel. Large area chemical vapor deposited monolayer MoS2 tends to be polycrystalline with intrinsic grain boundaries (GBs) Topological defects and grain size skillfully alter its physical properties in a variety of materials; however, the polycrystallinity and its role played in the mechanical performance of the emerging single layer MoS2 remain largely unknown. Here, using large scale atomistic simulations, GB structures and mechanical characteristics of realistic single layered polycrystalline MoS2 of varying grain size prepared by confinement quenched method are investigated. Depending on misorientation angle, structural energetics of polar GBs in polycrystals favor diverse dislocation cores, consistent with experimental observations. Polycrystals exhibit grain size dependent thermally induced global out of plane deformation, although defective GBs in MoS2 show planar structures that are in contrast to the graphene. Tensile tests show that presence of cohesive GBs pronouncedly deteriorates the in plane mechanical properties of MoS2. Both stiffness and strength follow an inverse pseudo Hall Petch relation to grain size, which is shown to be governed by the weakest link mechanism. Under uniaxial tension, transgranular crack propagates with small deflection, whereas upon biaxial stretching, the crack grows in a kinked manner with large deflection. These findings shed new light in GB based engineering and control of mechanical properties of MoS2 crystals toward real world applications in flexible electronics and nanoelectromechanical systems.
author_names: Jianyang Wu

Pinqiang Cao

Zhisen Zhang

Fulong Ning

Songsheng Zheng

Jianying He

Zhiliang Zhang
title: Grain Size Controlled Mechanical Properties of Polycrystalline Monolayer MoS2.
venue: Nano letters
year: 2018

abstract: Monolayer molybdenum disulfide (MoS2) a two dimensional semiconductor, possesses extraordinary physical properties and holds great promise for electronics, optoelectronics, and optics. However, the synthetic MoS2 samples usually comprise substantial structural defects, which greatly affect the device performance. Herein we comprehensively explore the atomic structures, energetic stability, and electronic and magnetic properties of grain boundaries (GBs) in monolayer MoS2 as well as the GBs decorated by antisite defects by first principles calculations. Eighteen types of GBs each carrying five kinds of antisite defects (a total of 108 defective systems) are constructed. The stability and magnetic properties of these defective monolayers are closely related to the type and number of homoelemental bonds. The GBs dominated by one type of homoelemental bond are ferromagnetic and have intrinsic magnetic moments up to 1.10 mB/nm. The GBs with equal number of defect rings that involve Mo Mo and S S bonds can exh.
author_names: Nan Gao

Yu Guo

Si Zhou

Yizhen Bai

Jijun Zhao
title: Structures and Magnetic Properties of MoS2 Grain Boundaries with Antisite Defects
year: 2017

abstract: Structural defects in the molybdenum disulfide (MoS2) monolayer are widely reported and greatly degrade the transport and photoluminescence. However, how they influence the optical absorption properties remains unclear. In this work, by employing many body perturbation theory calculations, we investigate the influence of sulfur vacancies (SVs) the main type of intrinsic defects in the MoS2 monolayer, on the optical absorption and exciton effect. Our calculations reveal that the presence of SVs creates localized midgap states in the bandgap, which results in a dramatic red shift of the absorption peak and stronger absorbance in the visible light and near infrared region. Nevertheless, the SVs can be finely repaired by oxygen passivation and are beneficial to the formation of the stable localized excitons, which greatly enhance the optical absorption in the spectral range. The defect mediated/ engineered absorption mechanism is well understood, which offers insightful guides for improving the performance of two dimensional dichalcogenide based optoelectronic devices.
author_names: Huabing Shu

Yunhai Li

Xianghong Niu

Jinlan Wang
title: Greatly Enhanced Optical Absorption of a Defective MoS2 Monolayer through Oxygen Passivation.
venue: ACS applied materials interfaces
year: 2016

abstract: Abstract In this paper, the mechanical properties of single layer Molybdenum disulfide (SLMoS2) containing point defects, such as vacancies, or extra Sulfur (S) or Molybdenum (Mo) atoms are investigated by molecular dynamics (MD) simulations. It was found that the single S vacancy is most probable as the formation energy is the lowest among all point defects. Other antisite defects having a Mo atom replaced by two S atoms are the least possible ones. The structures of antisite defects are also unstable. The Young's modulus of planner SLMoS2 with defect is found to be within the scatter margin of pristine MoS2 sheet (without defects) The effect of temperature on each type of defect has been studied and it is found that strength is more affected by vacancies than it is by phase transition.
author_names: Avik Kumar Mahata

Jin-Wu Jiang

Debiprosad Roy Mahapatra

Timon Rabczuk
title: Effect of intrinsic structural defects on mechanical properties of single layer MoS2
venue: Nano Structures Nano Objects
year: 2019

abstract: Transition metal carbides (MXenes) with formula Mn+1CnTx (n 2 and 3) have been emerging as a new family of two dimensional (2D) materials that have great potential in electronic applications and CO2 conversion catalysts. It has been already found that the electronic and electrochemical properties of Ti3C2Tx MXenes can be tuned by replacing the two outer titanium layers with molybdenum layers. Similar to other 2D materials, intrinsic defects can be formed in the synthesized MXene flakes and the formation of defects can influence the performance of these materials. Herein, we systematically study the effect of the different types of structural defects on the structural stability, electronic behavior, and electrochemical properties of ordered Mo2TiC2Tx terminated with the specific surface functional groups of fluorine, oxygen, and hydroxide. The calculated defect formation energies imply that the formation of defects is dependent on the surface terminations, where the O terminated MXenes demand more energy than the F and OH terminated MXenes. We found that defect formation is more feasible in the outer molybdenum layers than in the inner titanium layer. Our results predicted that the CO2 molecule adsorbs on the defective surfaces through a spontaneous and exothermic process that is critical to its capture, while the perfect surface weakly attracts the molecule through a nonspontaneous and endothermic process. Thus, our study predicts that the electronic and electrochemical properties of Mo2TiC2Tx can be tuned by forming specific defects and these MXenes could be promising materials for CO2 adsorption and conversion.
author_names: Rasoul Khaledialidusti

Abhishek Kumar Mishra

Afrooz Barnoush
title: Atomic defects in monolayer ordered double transition metal carbide (Mo2TiC2Tx) MXene and CO2 adsorption
year: 2020