Two-dimensional materials are attractive for use in next-generation nanoelectronic devices because, compared to one-dimensional materials, it is relatively easy to fabricate complex structures from them. The most widely studied two-dimensional material is graphene, both because of its rich physics and its high mobility. However, pristine graphene does not have a bandgap, a property that is essential for many applications, including transistors. Engineering a graphene bandgap increases fabrication complexity and either reduces mobilities to the level of strained silicon films or requires high voltages. Although single layers of MoS(2) have a large intrinsic bandgap of 1.8 eV (ref. 16), previously reported mobilities in the 0.5-3 cm(2) V(-1) s(-1) range are too low for practical devices. Here, we use a halfnium oxide gate dielectric to demonstrate a room-temperature single-layer MoS(2) mobility of at least 200 cm(2) V(-1) s(-1), similar to that of graphene nanoribbons, and demonstrate transistors with room-temperature current on/off ratios of 1 × 10(8) and ultralow standby power dissipation. Because monolayer MoS(2) has a direct bandgap, it can be used to construct interband tunnel FETs, which offer lower power consumption than classical transistors. Monolayer MoS(2) could also complement graphene in applications that require thin transparent semiconductors, such as optoelectronics and energy harvesting.

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Single-layer MoS2 transistors

Novel physical phenomena can emerge in low-dimensional nanomaterials. Bulk MoS2, a prototypical metal dichalcogenide, is an indirect bandgap semiconductor with negligible photoluminescence. When the MoS2 crystal is thinned to monolayer, however, a strong photoluminescence emerges, indicating an indirect to direct bandgap transition in this d-electron system. This observation shows that quantum confinement in layered d-electron materials like MoS2 provides new opportunities for engineering the electronic structure of matter at the nanoscale.

Emerging Photoluminescence in Monolayer MoS2

Graphene-Like Two-Dimensional Materials

Molybdenum disulfi de (MoS 2 ) is systematically studied using Raman spectroscopy with ultraviolet and visible laser lines. It is shown that only the Raman frequencies of E 1 and A1g peaks vary monotonously with the layer number of ultrathin MoS 2 fl akes, while intensities or widths of the peaks vary arbitrarily. The coupling between electronic transitions and phonons are found to become weaker when the layer number of MoS 2 decreases, attributed to the increased electronic transition energies or elongated intralayer atomic bonds in ultrathin MoS 2 . The asymmetric Raman peak at 454 cm − 1 , which has been regarded as the overtone of longitudinal optical M phonons in bulk MoS 2 , is actually a combinational band involving a longitudinal acoustic mode (LA(M)) and an optical mode ( A2u ). Our fi ndings suggest a clear evolution of the coupling between electronic transition and phonon when MoS 2 is scaled down from three- to two-dimensional geometry.

From bulk to monolayer MoS2: evolution of Raman scattering

Large-area MoS(2) atomic layers are synthesized on SiO(2) substrates by chemical vapor deposition using MoO(3) and S powders as the reactants. Optical, microscopic and electrical measurements suggest that the synthetic process leads to the growth of MoS(2) monolayer. The TEM images verify that the synthesized MoS(2) sheets are highly crystalline.

Synthesis of Large‐Area MoS2 Atomic Layers with Chemical Vapor Deposition

We report on the synthesis, structure, and self-assembly of single-wall subnanometer-diameter molybdenum disulfide tubes. The nanotubes are up to hundreds of micrometers long and display diverse self-assembly properties on different length scales, ranging from twisted bundles to regularly shaped "furry" forms. The bundles, which contain interstitial iodine, can be readily disassembled into individual molybdenum disulfide nanotubes. The synthesis was performed using a novel type of catalyzed transport reaction including C(60) as a growth promoter.

/pdf/self-assembly-of-subnanometer-diameter-single-wall-mos2-2b8yfxp3k3.pdf

Self-assembly of subnanometer-diameter single-wall MoS2 nanotubes.

We report on the properties of a new air-stable nanowire material with the chemical formula Mo6S3I6 .T he distinguishing features of the material are rapid one-step synthesis, easy isolation and controllable dispersion into small-diameter wire bundles. Elemental analysis, x-ray diffraction, thermogravimetry, differential thermal analysis, Raman scattering and electron microscopy were used to characterize the material.

https://iopscience.iop.org/article/10.1088/0957-4484/15/5/039/pdf

Air-stable monodispersed Mo 6 S 3 I 6 nanowires

Hydrotreatment of liquefied lignocellulosic biomass was investigated at 300 °C under the total pressure of 8 MPa in a slurry reactor over unsupported molybdenum (disulphide, dioxide and carbide) and tungsten (disulphide) catalysts. Novel nanostructured urchin-like MoS2 and inorganic-fullerene MoS2 interconnected with carbon materials were synthetized and tested, while the influence of metal variation and the sulphide replacement with carbide or oxide was also investigated by using commercially available MoS2, Mo2C, MoO2 and WS2. Catalysts were structurally characterised by field-emission scanning (SEM) and high-resolution transmission (HRTEM) electron microscopies, energy-dispersive X-ray (EDX) and Raman spectroscopies, as well as X-ray diffraction (XRD). The hydrodeoxygenation (HDO), decarbonylation, decarboxylation and hydrocracking kinetics of depolymerised cellulose, hemicellulose and lignin were determined according to the transformation of their functional groups in liquid phase, and the corresponding gaseous products by an innovative lumped kinetic model based on Fourier transform infrared spectroscopy. Unsupported MoS2 catalysts showed high hydrogenolysis selectivity, the morphology clearly affecting its rate. A high HDO activity reflected in the mass balance and phase distribution of the upgraded liquid product by reducing tar residue and increasing the yield of oil phase with the gross calorific value of 38 MJ kg−1 and oxygen content below 8.5 wt%.

Hydrodeoxygenation of solvolysed lignocellulosic biomass by unsupported MoS2, MoO2, Mo2C and WS2 catalysts

Raman scattering of the MoS2 and WS2 single nanotubes

Reference EPFL-ARTICLE-150098doi:10.1002/adma.200304549View record in Web of Science Record created on 2010-07-21, modified on 2016-08-08

Adolf Jesih

Papers

Self-assembly of subnanometer-diameter single-wall MoS2 nanotubes.

Air-stable monodispersed Mo 6 S 3 I 6 nanowires

Hydrodeoxygenation of solvolysed lignocellulosic biomass by unsupported MoS2, MoO2, Mo2C and WS2 catalysts

Raman scattering of the MoS2 and WS2 single nanotubes

Shear and Young's Moduli of MoS2 Nanotube Ropes