Single-layer metal dichalcogenides are two-dimensional semiconductors that present strong potential for electronic and sensing applications complementary to that of graphene.

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Electronics and optoelectronics of two-dimensional transition metal dichalcogenides.

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

Ultrathin two-dimensional nanosheets of layered transition metal dichalcogenides (TMDs) are fundamentally and technologically intriguing. In contrast to the graphene sheet, they are chemically versatile. Mono- or few-layered TMDs - obtained either through exfoliation of bulk materials or bottom-up syntheses - are direct-gap semiconductors whose bandgap energy, as well as carrier type (n- or p-type), varies between compounds depending on their composition, structure and dimensionality. In this Review, we describe how the tunable electronic structure of TMDs makes them attractive for a variety of applications. They have been investigated as chemically active electrocatalysts for hydrogen evolution and hydrosulfurization, as well as electrically active materials in opto-electronics. Their morphologies and properties are also useful for energy storage applications such as electrodes for Li-ion batteries and supercapacitors.

http://nanotubes.rutgers.edu/PDFs/nchem_TMDs_2013.pdf

The chemistry of two-dimensional layered transition metal dichalcogenide nanosheets

The surface science of titanium dioxide

TiO2 photocatalysis and related surface phenomena

Single-layer MoS2 is an attractive semiconducting analogue of graphene that combines high mechanical flexibility with a large direct bandgap of 1.8 eV. On the other hand, bulk MoS2 is an indirect bandgap semiconductor similar to silicon, with a gap of 1.2 eV, and therefore deterministic preparation of single MoS2 layers is a crucial step toward exploiting the large direct bandgap of monolayer MoS2 in electronic, optoelectronic, and photovoltaic applications. Although mechanical and chemical exfoliation methods can be used to obtain high quality MoS2 single layers, the lack of control in the thickness, shape, size, and position of the flakes limits their usefulness. Here we present a technique for controllably thinning multilayered MoS2 down to a single-layer two-dimensional crystal using a laser. We generate single layers in arbitrary shapes and patterns with feature sizes down to 200 nm and show that the resulting two-dimensional crystals have optical and electronic properties comparable to that of prist...

Laser-Thinning of MoS2: On Demand Generation of a Single-Layer Semiconductor

Efficient carrier multiplication has been reported for several semiconductor nanocrystals: PbSe, PbS, PbTe, CdSe, InAs, and Si. Some of these reports have been challenged by studies claiming that carrier multiplication does not occur in CdSe, CdTe, and InAs nanocrystals, thus raising legitimate doubts concerning the occurrence of carrier multiplication in the remaining materials. Here, conclusive evidence is given for its occurrence in PbSe nanocrystals using femtosecond transient photobleaching. In addition, it is shown that a correct determination of carrier-multiplication efficiency requires spectral integration over the photobleach feature. The carrier multiplication efficiency we obtain is significantly lower than what has been reported previously, and it remains an open question whether it is higher in nanocrystals than it is in bulk semiconductors.

In spite of recent doubts carrier multiplication does occur in PbSe nanocrystals.

Visible light sensitisation of titanium dioxide using a phenylene vinylene polymer

Recently, much attention has been focused on the use of nanostructured metal oxide semiconductors for various applications, such as electrochromic windows, photocatalytic devices, lithium-ion batteries, dielectrics in integrated circuits, and dye-sensitized TiO{sub 2} solar cells. Smooth nanometer-scale films of anatase TiO{sub 2} on indium-tin oxide substrates (ITO) are obtained by electron-beam evaporation of reduced TiO{sub 2} powder. Mott-Schottky analysis shows an abrupt change in slope when the depletion layer reaches the TiO{sub 2}/ITO interface. An electrostatic model is derived, which gives a quantitative description of the observed change in slope. From the potential at which the slope changes, the dielectric constant of anatase could be accurately determined. A value of 55 is found, which is significantly lower than those reported for anatase TiO{sub 2}.

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Mott-Schottky analysis of nanometer-scale thin-film anatase TiO2

Current research on lithium-ion intercalation materials focuses on the development of cheap and efficient lithium-ion batteries. Nanostructured anatase TiO{sub 2} is an interesting candidate as electrode material in rocking-chair type lithium batteries. In addition to its ability to store charge in the form of lithium ions, it also exhibits electrochromic properties, and has attracted widespread attention with regard to its use in dye-sensitized solar cells. Electrochemical lithium intercalation in thin films of porous nanostructured TiO{sub 2} and dense electron-beam evaporated TiO{sub 2} (anatase) is investigated with in situ X-ray diffraction (XRD). A complete and reversible phase transformation from tetragonal anatase TiO{sub 2} to orthorhombic anatase Li{sub 0.5}TiO{sub 2} is observed. The maximum amount of lithium that can be dissolved in anatase TiO{sub 2} before the phase transformation occurs is estimated to be 0.05 Li/Ti. For nanostructured samples, the XRD spectra before and after insertion were fitted with some of the lattice parameters of the two phases as fit variables. For the Li{sub 0.5}TiO{sub 2} phase, values of 3.85, 4.06, and 8.95 {angstrom} are found for the a, b, and c, axes, respectively, in good agreement with data reported for chemically lithiated anatase TiO{sub 2} powder. Implications of the phase transitionmore » for the analysis of optical and electrochemical measurements on TiO{sub 2} films are briefly discussed.« less

Albert Goossens

Papers

Laser-Thinning of MoS2: On Demand Generation of a Single-Layer Semiconductor

In spite of recent doubts carrier multiplication does occur in PbSe nanocrystals.

Visible light sensitisation of titanium dioxide using a phenylene vinylene polymer

Mott-Schottky analysis of nanometer-scale thin-film anatase TiO2

In Situ X‐Ray Diffraction of Lithium Intercalation in Nanostructured and Thin Film Anatase TiO2