Search

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]

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]

Abstract: Large area nitrogen (N)-doped graphene films were grown on copper foil by chemical vapor deposition. The as-grown films consisted of a single atomic layer that was continuous across the copper surface steps and grain boundaries, and could be easily transferred to a variety of substrates. N-doping was confirmed by X-ray photoelectron spectroscopy, Raman spectroscopy, and elemental mapping. N atoms were suggested to mainly form a “pyrrolic” nitrogen structure, and the doping level of N reached up to 3.4at.%. The N-doped graphene exhibited an n-type behavior, and nitrogen doping would open a band gap in the graphene. This study presents use of a new liquid precursor to obtain large area, continuous and mostly single atom layer N-doped graphene films. [Copyright &y& Elsevier]