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Novel near-infrared emission from crystal defects in MoS₂ multilayer flakes.

ABSTRACT: The structural defects in two-dimensional transition metal dichalcogenides, including point defects, dislocations and grain boundaries, are scarcely considered regarding their potential to manipulate the electrical and optical properties of this class of materials, notwithstanding the significant advances already made. Indeed, impurities and vacancies may influence the exciton population, create disorder-induced localization, as well as modify the electrical behaviour of the material. Here we report on the experimental evidence, confirmed by ab initio calculations, that sulfur vacancies give rise to a novel near-infrared emission peak around 0.75?eV in exfoliated MoS₂ flakes. In addition, we demonstrate an excess of sulfur vacancies at the flake's edges by means of cathodoluminescence mapping, aberration-corrected transmission electron microscopy imaging and electron energy loss analyses. Moreover, we show that ripplocations, extended line defects peculiar to this material, broaden and redshift the MoS₂ indirect bandgap emission.

SUBMITTER: Fabbri F

PROVIDER: S-EPMC5059461 | biostudies-literature | 2016 Oct

REPOSITORIES: biostudies-literature

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Novel near-infrared emission from crystal defects in MoS<sub>2</sub> multilayer flakes.

Fabbri F F Rotunno E E Cinquanta E E Campi D D Bonnini E E Kaplan D D Lazzarini L L Bernasconi M M Ferrari C C Longo M M Nicotra G G Molle A A Swaminathan V V Salviati G G

Nature communications 20161004

The structural defects in two-dimensional transition metal dichalcogenides, including point defects, dislocations and grain boundaries, are scarcely considered regarding their potential to manipulate the electrical and optical properties of this class of materials, notwithstanding the significant advances already made. Indeed, impurities and vacancies may influence the exciton population, create disorder-induced localization, as well as modify the electrical behaviour of the material. Here we re ...[more]

PMID: 27698425

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Project description:Tribological studies of the 2D nanoadditives such as MoS2 and graphene are mostly performed in base oils such as SN500, SN150, or paraffin. We have focused on their effect in lubrication properties of industrial oils (e.g., axle, transmission, and compressor oils) along with SN500 oil employing a four-ball tester. Two types of graphene powders (GpowA with fewer defects than GpowC), MoS2 powder, and their physical mixtures are chosen as nanoadditives. The tribology performance for 0.05 wt% of additives in various industrial oils is evaluated by monitoring the coefficient of friction (COF) during rubbing and wear scar diameter (WSD) of the steel balls after rubbing. Elemental analysis and electron microscopy have been performed on the wear surfaces for evidence of any tribofilm formation. GpowA favors antifriction for axle and transmission oils with 40% reduction in axle oil, whereas it improved antiwear properties in most of the oils. GpowC shows a COF decrement by 12% only for compressor oil, but contribute to wear reduction in all oils. The observed COF reduction is attributed to the compatibility of nonfunctionalized GpowA with nonpolar axle oil and functionalized GpowC with polar compressor oil. MoS2 shows a decrease in the COF and WSD in most industrial oils; the best being 60% COF and 7% WSD reduction in axle oil. For additives in oils that favor antiwear, flakes or particles are observed on the wear surface supported by the higher elemental contribution of the constituents from the wear region. The mixtures of GpowA or C with MoS2, however, does not seem to favor improvement in the COF or WSD in industrial oils. With assistance from oleylamine surfactants, the lubrication properties of most additives are improved, particularly for the mixtures with 12-15% COF reduction and 4-7% WSD reduction in compressor oil. The study indicates that a large sheet size of high-quality graphene aids antifriction and addition of surfactant molecules facilitates a co-operative effect between MoS2 and graphene for improved tribology.

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Novel near-infrared emission from crystal defects in MoS₂ multilayer flakes.

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Novel near-infrared emission from crystal defects in MoS<sub>2</sub> multilayer flakes.

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Novel near-infrared emission from crystal defects in MoS2 multilayer flakes.

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Novel near-infrared emission from crystal defects in MoS<sub>2</sub> multilayer flakes.

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OmicsDI is part of the ELIXIR infrastructure

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Novel near-infrared emission from crystal defects in MoS₂ multilayer flakes.