Transparent conductors—A status review

A major area of application for nanowires and nanotubes is likely to be the sensing of important molecules, either for medical or environmental health purposes. The ultrahigh surface-to-volume ratios of these structures make their electrical properties extremely sensitive to surface-adsorbed species, as recent work has shown with carbon nanotubes,[1, 2] functionalized silicon nanowires and metal nanowires.[3, 4] Chemical nanosensors are interesting because of their potential for detecting very low concentrations of biomolecules or pollutants on platforms small enough to be used in vivo or on a microchip. Here we report the development of photochemical NO2 sensors that work at room temperature and are based on individual single-crystalline SnO2 nanoribbons. Tin dioxide is a wide-bandgap (3.6 eV) semiconductor. For n-type SnO2 single crystals, the intrinsic carrier concentration is primarily determined by deviations from stoichiometry in the form of equilibrium oxygen vacancies, which are predominantly atomic defects.[5] The electrical conductivity of nanocrystalline SnO2 depends strongly on surface states produced by molecular adsorption that results in space-charge layer changes and band modulation.[6] NO2, a combustion product that plays a key role in tropospheric ozone and smog formation, acts as an electron-trapping adsorbate on SnO2 crystal faces and can be sensed by monitoring the electrical conductance of the material. Because NO2 chemisorbs strongly on many metal oxides,[7] commercial sensors based on particulate or thin-film SnO2 operate at 300 ± 500 C to enhance the surface molecular desorption kinetics and continuously TMclean∫ the sensors.[8] The high-temperature operation of these oxide sensors is not favorable in many cases, particularly in an explosive environment. We have found that the strong photoconducting response of individual singlecrystalline SnO2 nanoribbons makes it possible to achieve equally favorable adsorption ± desorption behavior at room temperature by illuminating the devices with ultraviolet (UV) light of energy near the SnO2 bandgap. The active desorption process is thus photoinduced molecular desorption (Figure 1).[9] In conclusion, we have succeeded in the development of the ruthenium-based metathesis catalyst 4, which exhibits excellent metathesis activity, without any loss of stability in air. These findings once again demonstrate that seemingly small variations in ligand structure can result in significant improvements in catalysis.

Photochemical Sensing of NO2 with SnO2 Nanoribbon Nanosensors at Room Temperature

The prosperity of human society largely relies on safe energy supply, and fossil fuel has been serving as the most reliable energy source. However, as a non-renewable energy source, the exhaustion of fossil fuel is inevitable and imminent in this century. To address this problem, renewable energy especially solar energy has attracted much attention, because it directly converts solar energy into electrical power leaving no environment affect. In the past, various photovoltaic devices like organic, inorganic, and hybrid solar cells were fabricated in succession. In spite of high conversion rate of silicon based solar cells, the high module cost and complicated production process restricted their application solely to astronautic and aeronautic technology. For domestic and other commercial applications, research has been focused on organic solar cells for their inherent low module cost and easy fabrication. In addition, organic solar cells have their lightweight and flexibility advantage over conventional silicon-based crystalline solar cells. Among all the organic solar cells, dye-sensitized solar cells (DSSCs) are the most efficient and easily implemented technology. Here, this study examines the working principle, present development and future prospectus for this novel technology.

Review on dye-sensitized solar cells (DSSCs): Fundamental concepts and novel materials

Surface processes in the detection of reducing gases with SnO2-based devices

TiO2‐Coated Multilayered SnO2 Hollow Microspheres for Dye‐Sensitized Solar Cells

Single crystals of the wide bandgap semiconductor stannic oxide, SnO2, have been grown and studied electrically. A chemical vapor deposition technique using chlorine transport, no inert carrier gases, and low pressure has been used to grow stannic oxide crystals of higher purity and with almost an order‐of‐magnitude higher low‐temperature Hall mobility, 8800 cm2/V sec at 80°K, than have previously been available. Measurements of Hall mobility, carrier concentration, and resistivity have been made between 20 and 625°K on crystals with room‐temperature carrier concentrations between 8×1015 and 2×1018 cm−3. The effects of the crystal anisotropy on these measurements have been investigated and found to be small (all results reported are for the a direction). A donor level ∼35‐meV deep due to antimony and another level ascribed to oxygen vacancies at ∼140 meV have been observed. Polar optical mode scattering with a dominant characteristic temperature of 1080°C is the main carrier scattering mechanism above 250°K. Below 250°K acoustic deformation potential scattering dominates. Ionized impurity scattering is eventually important in all samples as the temperature is lowered. A polaron effective mass of 0.39 me has been found consistently in the analyses of the data. A technique of fabricating good Schottky barriers on SnO2 has also been developed and used to measure the net donor concentration in samples. The agreement found between these measurements and Nd from Hall measurements indicates that shallow trapping is not a problem in these crystals.

C. G. Fonstad

Papers

Electrical Properties of High‐Quality Stannic Oxide Crystals