236 research outputs found

    Spectroscopic study of double sulphides of molybdenum (IV) and rhenium (IV)

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    Dichalcogenides of transition metals are especially interesting. Majority of chalcoginides are semiconductors and some of them show interesting properties in certain regions of optical spectrum. Such properties allow application of these compounds in optico-electronics, radio-photonics, laser physics etc. Direct synthesis one of simple chalcogenides - rhenium disulphide - has been carried out from source components: metallic rhenium and elemental sulfur. In this research we used high temperature annealing at 1000 0C and the pressure of 10-5 atm in 24 hours. The synthesis was carried out in a sealed quartz ampoule. Photoelectron spectra and IR absorption spectra of molybdenum disulfide (IV) and rhenium disulfide (IV) were measured during the research. We shows that rhenium disulfide (IV) crystallize in CdI2 structural type. S2p sulfur bond energy for molybdenum disulfide (IV) and rhenium disulfide (IV) are at almost identical values. IR spectrum analysis shows that rhenium disulfide (IV) structure compared with molybdenum disulfide (IV)

    Spectroscopic study of double sulphides of molybdenum (IV) and rhenium (IV)

    Get PDF
    Dichalcogenides of transition metals are especially interesting. Majority of chalcoginides are semiconductors and some of them show interesting properties in certain regions of optical spectrum. Such properties allow application of these compounds in optico-electronics, radio-photonics, laser physics etc. Direct synthesis one of simple chalcogenides - rhenium disulphide - has been carried out from source components: metallic rhenium and elemental sulfur. In this research we used high temperature annealing at 1000 0C and the pressure of 10-5 atm in 24 hours. The synthesis was carried out in a sealed quartz ampoule. Photoelectron spectra and IR absorption spectra of molybdenum disulfide (IV) and rhenium disulfide (IV) were measured during the research. We shows that rhenium disulfide (IV) crystallize in CdI2 structural type. S2p sulfur bond energy for molybdenum disulfide (IV) and rhenium disulfide (IV) are at almost identical values. IR spectrum analysis shows that rhenium disulfide (IV) structure compared with molybdenum disulfide (IV)

    Prevalence of oxygen defects in an in-plane anisotropic transition metal dichalcogenide

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    Atomic scale defects in semiconductors enable their technological applications and realization of novel quantum states. Using scanning tunneling microscopy and spectroscopy complemented by ab-initio calculations we determine the nature of defects in the anisotropic van der Waals layered semiconductor ReS2_2. We demonstrate the in-plane anisotropy of the lattice by directly visualizing chains of rhenium atoms forming diamond-shaped clusters. Using scanning tunneling spectroscopy we measure the semiconducting gap in the density of states. We reveal the presence of lattice defects and by comparison of their topographic and spectroscopic signatures with ab initio calculations we determine their origin as oxygen atoms absorbed at lattice point defect sites. These results provide an atomic-scale view into the semiconducting transition metal dichalcogenides, paving the way toward understanding and engineering their properties.Comment: 9 pages, 4 figures; Supp 5 pages, 4 figure

    Synthesis of ultrathin rhenium disulfide nanoribbons using nano test tubes

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    The synthesis of ultrathin rhenium disulfide (ReS2) nanoribbons within single-walled carbon nanotubes (SWNTs) has been established. Dirhenium decacarbonyl complex is encapsulated into the SWNTs to provide a source of confined rhenium atoms, which readily react with iodine to form discrete nm-sized clusters of rhenium iodide [Re6I14]2− embedded in the nanotubes. The final step of the synthesis is accomplished by admitting hydrogen sulfide gas into nano test tubes, yielding twisted nanoribbons of rhenium disulfide encapsulated in carbon nanotubes, ReS2@SWNTs. The width, structure, and composition of rhenium disulfide nanoribbons are strictly controlled by the extreme confinement of the host-SWNT. A holistic analytical approach combining complementary imaging and analysis methods is used at each synthetic step to elucidate the structure and composition of the guest material and reveal the role of the SWNT contributing towards the electronic interactions with encapsulated inorganic structures. As ReS2 nanoribbons are expected to retain the electronic properties of the bulk material, such as direct bandgap, the low dimensional form of this material can be of interest for use in nanoscale electronic devices

    Novel Growth Routes and Fundamental Understanding of Pseudo-One-Dimensional Materials

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    abstract: Recently, two-dimensional (2D) materials have emerged as a new class of materials with highly attractive electronic, optical, magnetic, and thermal properties. However, there exists a sub-category of 2D layers wherein constituent metal atoms are arranged in a way that they form weakly coupled chains confined in the 2D landscape. These weakly coupled chains extend along particular lattice directions and host highly attractive properties including high thermal conduction pathways, high-mobility carriers, and polarized excitons. In a sense, these materials offer a bridge between traditional one-dimensional (1D) materials (nanowires and nanotubes) and 2D layered systems. Therefore, they are often referred as pseudo-1D materials, and are anticipated to impact photonics and optoelectronics fields. This dissertation focuses on the novel growth routes and fundamental investigation of the physical properties of pseudo-1D materials. Example systems are based on transition metal chalcogenide such as rhenium disulfide (ReS2), titanium trisulfide (TiS3), tantalum trisulfide (TaS3), and titanium-niobium trisulfide (Nb(1-x)TixS3) ternary alloys. Advanced growth, spectroscopy, and microscopy techniques with density functional theory (DFT) calculations have offered the opportunity to understand the properties of these materials both experimentally and theoretically. The first controllable growth of ReS2 flakes with well-defined domain architectures has been established by a state-of-art chemical vapor deposition (CVD) method. High-resolution electron microscopy has offered the very first investigation into the structural pseudo-1D nature of these materials at an atomic level such as the chain-like features, grain boundaries, and local defects. Pressure-dependent Raman spectroscopy and DFT calculations have investigated the origin of the Raman vibrational modes in TiS3 and TaS3, and discovered the unusual pressure response and its effect on Raman anisotropy. Interestingly, the structural and vibrational anisotropy can be retained in the Nb(1-x)TixS3 alloy system with the presence of phase transition at a nominal Ti alloying limit. Results have offered valuable experimental and theoretical insights into the growth routes as well as the structural, optical, and vibrational properties of typical pseudo-1D layered systems. The overall findings hope to shield lights to the understanding of this entire class of materials and benefit the design of 2D electronics and optoelectronics.Dissertation/ThesisDoctoral Dissertation Materials Science and Engineering 201
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