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.

/pdf/single-layer-mos2-transistors-6go64w4t3p.pdf

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 ...

/pdf/dye-sensitized-solar-cells-50b0w2bhsr.pdf

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

Photoelectronic properties of the p-type layered trichalcogenophosphates FePS3 and FePSe3

Raman scattering in quasi-one-dimensional ZrTe5

Structural analysis of 2H–WS2 thin films by X-ray and TEM investigation

Titanium chromium oxide thin films were deposited by a DC reactive magnetron sputtering from separate Ti and Cr metallic targets in a reactive atmosphere. A constant current density J Ti =150 A m −2 was used to sputter the titanium target, whereas the current density on the chromium target was systematically changed from J Cr =0–200 A m −2 . X-Ray diffraction, electron probe microanalysis and atomic force microscopy were used to investigate the effect of an increasing current density of the chromium target on the structural, compositional and morphological parameters of the coatings. A continuous evolution of the Ti x Cr 1 −x O y composition was observed ( x =1–0.34 and y =2–1.7), whereas an amorphisation of the material and a maximum of the surface roughness was obtained for J Cr =50–100 A m −2 . In the same way, energy distribution of the neutral and ionic species impinging on the surface of the growing film were determined by energy-resolved mass spectrometry. Mean energies and the relative fluxes of positive and negative ions were determined from their energy distributions. The behaviour of these species was also affected by the chromium current density especially between J Cr =50 and 100 A m −2 . Similarities in the changes of the thin films properties and the characteristics of ionic species are discussed, so as to establish some relationships between the plasma parameters and the deposited films.

Intrinsic low energy bombardment of titanium chromium oxide thin films prepared by reactive sputtering

The behaviour of oxygen impurities during rapid thermal processing of Ti/Si diffusion couples has been studied between 480 and 800 degrees C. Samples were prepared by sputter deposition of 40 nm of titanium of (001) silicon wafers which were then annealed in ambient argon. The investigation techniques included depth profiling using Auger electron spectroscopy, transmission electron microscopy, and electrical sheet resistance measurements. The oxygen impurity effects are mainly controlled by kinetic parameters, i.e. the silicide reaction rate and the oxygen diffusivity in titanium. At low temperatures, the oxygen contamination originating from the annealing furnace is the cause of major impurity effects. Below 550 degrees C the oxygen that spreads into the metal film blocks the silicide reaction while above 650 degrees C, silicide formation dominates over oxygen diffusion and contamination-free silicide is produced. From 550 to 600 degrees C, the competition between silicide reaction and oxygen diffusion results in the formation of a silicon-deficient, oxygen-rich Ti-Si-O sublayer on top of the silicide. This layer appears to be composed of TiOx and TiSi2. In some cases, all Ti is reacted but oxygen remains in the layer and the morphology of the silicide is strongly affected. In any case, the only crystalline silicide phase that forms is TiSi2, and not TiSi or Ti5Si3, as confirmed by electron diffraction and high-resolution electron microscopy.

Francis Lévy

Papers

Photoelectronic properties of the p-type layered trichalcogenophosphates FePS3 and FePSe3

Raman scattering in quasi-one-dimensional ZrTe5

Structural analysis of 2H–WS2 thin films by X-ray and TEM investigation

Intrinsic low energy bombardment of titanium chromium oxide thin films prepared by reactive sputtering

Oxygen impurity effects on the formation of thin titanium silicide films by rapid thermal annealing