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Despite its importance in the large-scale synthesis of transition metal dichalcogenides (TMDC) molecular layers, the generic quantum effects on electrical transport across individual grain boundaries (GBs) in TMDC monolayers remain unclear. Here we demonstrate that strong carrier localization due to the increased density of defects determines both temperature dependence of electrical transport and low-frequency noise at the GBs of chemical vapor deposition (CVD)-grown MoS2 layers. Using field effect devices designed to explore transport across individual GBs, we show that the localization length of electrons in the GB region is -30-70% lower than that within the grain, even though the room temperature conductance across the GB, oriented perpendicular to the overall flow of current, may be lower or higher than the intragrain region. Remarkably, we find that the stronger localization is accompanied by nearly 5 orders of magnitude enhancement in the low-frequency noise at the GB region, which increases exponentially when the temperature is reduced. The microscopic framework of electrical transport and noise developed in this paper may be readily extended to other strongly localized two-dimensional systems, including other members of the TMDC family. [ABSTRACT FROM AUTHOR]

Wedemonstrate how substrate interfacial chemistry can be utilizedto tailor the physical properties of single-crystalline molybdenumdisulfide (MoS2) atomic-layers. Semiconducting, two-dimensionalMoS2possesses unique properties that are promising forfuture optical and electrical applications for which the ability totune its physical properties is essential. We use self-assembled monolayerswith a variety of end termination chemistries to functionalize substratesand systematically study their influence on the physical propertiesof MoS2. Using electrical transport measurements, temperature-dependentphotoluminescence spectroscopy, and empirical and first-principlescalculations, we explore the possible mechanisms involved. Our datashows that combined interface-related effects of charge transfer,built-in molecular polarities, varied densities of defects, and remoteinterfacial phonons strongly modify the electrical and optical propertiesof MoS2. These findings can be used to effectively enhanceor modulate the conductivity, field-effect mobility, and photoluminescencein MoS2monolayers, illustrating an approach for localand universal property modulations in two-dimensional atomic-layers. [ABSTRACT FROM AUTHOR]

Monolayermolybdenum disulfide (MoS2) with a directband gap of 1.8 eV is a promising two-dimensional material with apotential to surpass graphene in next generation nanoelectronic applications.In this Letter, we synthesize monolayer MoS2on Si/SiO2substrate via chemical vapor deposition (CVD) method andcomprehensively study the device performance based on dual-gated MoS2field-effect transistors. Over 100 devices are studied toobtain a statistical description of device performance in CVD MoS2. We examine and scale down the channel length of the transistorsto 100 nm and achieve record high drain current of 62.5 mA/mm in CVDmonolayer MoS2film ever reported. We further extract theintrinsic contact resistance of low work function metal Ti on monolayerCVD MoS2with an expectation value of 175 Ω·mm,which can be significantly decreased to 10 Ω·mm by appropriategating. Finally, field-effect mobilities (μFE) ofthe carriers at various channel lengths are obtained. By taking theimpact of contact resistance into account, an average and maximumintrinsic μFEis estimated to be 13.0 and 21.6 cm2/(V s) in monolayer CVD MoS2films, respectively. [ABSTRACT FROM AUTHOR]

Monolayer molybdenum disulfide (MoS2) is a two-dimensionaldirect band gap semiconductor with unique mechanical, electronic,optical, and chemical properties that can be utilized for novel nanoelectronicsand optoelectronics devices. The performance of these devices stronglydepends on the quality and defect morphology of the MoS2layers. Here we provide a systematic study of intrinsic structuraldefects in chemical vapor phase grown monolayer MoS2, includingpoint defects, dislocations, grain boundaries, and edges, via directatomic resolution imaging, and explore their energy landscape andelectronic properties using first-principles calculations. A richvariety of point defects and dislocation cores, distinct from thosepresent in graphene, were observed in MoS2. We discoverthat one-dimensional metallic wires can be created via two differenttypes of 60° grain boundaries consisting of distinct 4-fold ringchains. A new type of edge reconstruction, representing a transitionstate during growth, was also identified, providing insights intothe material growth mechanism. The atomic scale study of structuraldefects presented here brings new opportunities to tailor the propertiesof MoS2via controlled synthesis and defect engineering. [ABSTRACT FROM AUTHOR]