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

BiCaSrCuO-Semiconductor interface formation processes

Low temperature thermal conductivity of quasi-one dimensional compounds (NbSe4)3I and (TaSe4)2I

Ti–Ge–N single-layer and TiN/GeN-multilayer thin films were deposited by reactive magnetron sputtering on Si and WC–Co substrates at constant temperature T s  = 240 °C, from confocal Ti and Ge targets in a mixed Ar/N 2 atmosphere. The nitrogen partial pressure, the TiN deposition time t Ti and the power on the Ti and Ge targets were kept constant. In order to obtain various GeN layer thicknesses in the films, the deposition time ratio t Ge / t Ti was varied. TiN/GeN multilayer films with TiN thickness ∼ 5 nm and various GeN thicknesses between 0.5 and 5 nm were deposited. A nanocrystalline multilayer film is formed, where the suppression of crystal growth is controlled by the successive deposition of two phases. TEM investigations revealed important changes induced by GeN x thickness variation: the columnar single-layer morphology switches into a multilayer morphology. The critical GeN thickness for changing the type of morphology is controlled by the diffusion of Ge atoms at the TiN crystallite boundaries. The morphology modification from single-layer to multilayer type determines the film hardening. Electron probe microanalyses (EPMA), scanning tunneling microscopy (STM), transmission electron microscopy (TEM), nanoindentation and X-ray diffraction (XRD) techniques were employed to characterize single- and multilayer films. The properties of alternate-deposited films are compared to those of co-deposited ones and interpreted.

Structural and chemical properties of sputter-deposited Ti–Ge–N thin films

The study of optical phenomena on the subwavelength scale is becoming increasingly important in photonics, particularly in the fields of nanoemitters, photonic crystals and plasmonics. Subwavelength field patterns are evanescent and must thus be investigated with near-field techniques. The light powers emitted by nanoscale sources are extremely low, undermining the traditional approach of scattering a near field to a large (thus noisy) far-field detector. Nanoscale detectors, providing direct sensing in the near-field with small noise due to a small active area, are needed in high-sensitivity, high-resolution near-field imaging and in quantum nanophotonic circuits. Here we report the first nanoscale ~50x50nm2) detector displaying single-photon sensitivity and a nanosecond response. These nanodetectors can also be operated in multi-photon mode, where the detection threshold can be set at N=1, 2, 3 or 4 photons, thus allowing the mapping of photon number statistics on the nanoscale.

Nanoscale single- and multi-photon mapping of optical fields

We present a novel concept of photon number resolving detector based on 120-nm-wide superconducting stripes made of
4-nm-thick NbN film and connected in parallel (PNR-SSPD). The detector consisting of 5 strips demonstrate a capability
to resolve up to 4 photons absorbed simultaneously with the single-photon quantum efficiency of 2.5% and negligibly
low dark count rate.

Francis Lévy

Papers

BiCaSrCuO-Semiconductor interface formation processes

Low temperature thermal conductivity of quasi-one dimensional compounds (NbSe4)3I and (TaSe4)2I

Structural and chemical properties of sputter-deposited Ti–Ge–N thin films

Nanoscale single- and multi-photon mapping of optical fields

Superconducting photon number resolving counter for near infrared applications