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

Titanium Dioxide Nanomaterials: Synthesis, Properties, Modifications, and Applications

Dye-sensitized solar cells (DSCs) offer the possibilities to design solar cells with a large flexibility in shape, color, and transparency. DSC research groups have been established around the worl ...

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Dye-Sensitized Solar Cells

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

TiO2 photocatalysis and related surface phenomena

Infrared optical properties of single crystals in the system Ti1−xHfxSe2

New Crystal Structures of WS2: Microtubes, Ribbons, and Ropes.

Near-normal incidence reflectivity measurements on layered single crystals of Ti1-xVxS2 with O<or=x<or=0.3 are presented. The experimental reflectivity spectra are discussed in terms of a dielectric function containing contributions from the valence electrons, the phonon and the free carriers. The spectrum of TiS2 is characterised by a very high reflectivity value in the far-infrared with a broad phonon feature of Eu symmetry superimposed at 158 cm-1. For the most stoichiometric TiS2 sample the authors deduce a carrier concentration of 2.8*1020 cm-3, assuming mopt approximately me. For V concentrations x=0.05 and 0.1 a decrease of the density of free carriers has been observed, attributed to a localisation of electrons in connection with V2+ impurity centres. The optical results are discussed in relation to data from transport measurements and photoemission work.

https://iopscience.iop.org/article/10.1088/0022-3719/16/8/020/pdf

Francis Lévy

Papers

Infrared optical properties of single crystals in the system Ti1−xHfxSe2

New Crystal Structures of WS2: Microtubes, Ribbons, and Ropes.

The influence of V impurities on the electronic and vibrational properties of TiS2 single crystals. I. Optical studies

Structural and optical properties of Pd1−xInx thin films

Chemical vapour transport of transition-metal oxides (II) epitaxial growth of RuO2, IrO2 and (Ru1−x, Irx)O2 on TiO2