R. Kershaw

The electrical, optical and photoconducting properties of Fe2−xCrxO3 (0 ⩽ x ⩽ 0.47)

Abstract A study has been made of the electrical, optical and photoconducting properties of pure and reduced single crystals of composition Fe 2− x Cr x O 3 where 0 ⩽ x ⩽ 0.47. It has been found that pure α-Fe 2 O 3 is not a photoconductor. When defect-free crystals of α-Fe 2 O 3 are reduced a surface layer of Fe 3 O 4 is formed and the crystals exhibit photoconductivity. Removal of this layer resulted in the disappearance of photocurrents and an increase in the sample resistivity. A necessary condition for the observation of photocurrents in n -type Fe 2 O 3 is that some Fe 3 O 4 be present. In addition, it has been found that the substitution of chromium for iron in α-Fe 2 O 3 results in a monotonically decreasing optical band gap as the chromium concentration, x , increases.

Preparation of zinc sulfide thin films by ultrasonic spray pyrolsis from bis(diethyldithiocarbamato) zinc(II)

Abstract Thin films of zinc sulfide were prepared by ultrasonically spraying a toluene solution of bis(diethyldithiocarbamato)zinc(II) onto silicon, sapphire and gallium arsenide substrates at 460–520 °C. The films prepared on silicon or sapphire were found to have a highly oriented hexagonal structure, while those deposited onto cubic (100) gallium arsenide showed a highly oriented cubic structure. The films were characterized by X-ray diffraction analysis, ellipsometry, scanning electron microscopy, and IR spectroscopy.

Characterization of n‐Type Semiconducting Tungsten Disulfide Photoanodes in Aqueous and Nonaqueous Electrolyte Solutions Photo‐oxidation of Halides with High Efficiency

Synthetic, single crystal, n-type semiconducting WS/sub 2/ (bandgap /approximately equals/ 1.3 eV) has been characterized as a photoanode in aqueous and nonaqueous electrolyte media. The WS/sub 2/ was synthesized from the elements by bromine and chlorine transport to yield plates up to 3* 3 mm in dimension. Interface characterization includes (i) cyclic voltammetry in the presence of a large number of fast, one-electron redox couples in CH/sub 3/CN/0.1M(/eta/-Bu/sub 4/N)ClO/sub 4/ solutions; (ii) steady-state photocurrent-voltage properties in aqueous and nonaqueous solutions of X/sup -/ (X/sup -/.Cl/sup -/, Br/sup -/, I/sup -/); (iii) tests of durability; (iv) wavelength dependence of photocurrent and photovoltage; and (v) high resolution (approximately 5 /mu/m) laser mapping of the surface to reveal surface inhomogeneity with respect to output photovoltage. 27 refs.

Preparation and characterization of cubic ZrO2 stabilized by Fe(III) and Fe(II)

Abstract Samples of cubic ZrO2 containing 2.5–40 at% Fe(III) were prepared by codecomposition of the nitrates. X-ray powder diffraction analysis and magnetic measurements indicated that α-Fe2O3 and ZrO2 form a solid solution up to 25 at% Fe Zr in the product. At this point, the solubility limit of a-Fe2O3 in ZrO2 is exceeded. The reduction of cubic zirconia samples containing 2.5–20 at% Fe(III) leads to the stabilization of iron(II) in the zirconia lattice. Reduction to metallic iron occurs at much higher temperatures than the reduction of bulk a-Fe2O3.

Improvement of photocatalytic activity of titanium (IV) oxide by dispersion of Au on TiO2

Abstract TiO2 samples were prepared by two procedures and their catalytic activities were compared to samples of commercial TiO2 (P25). The addition of gold to all of these samples increased their photocatalytic activity.

Preparation and characterization of TiO2 films by a novel spray pyrolysis method

Abstract Films of anatase were prepared on silicon and silica supports by ultrasonic nebulization of an ethanol solution of titanium acetylacetonate followed by pyrolysis and annealing in oxygen at 380°C. The transformation to rutile occurred in the temperature range 800–950°C without degradation of the film quality. TiO 2 films could be slightly reduced to TiO 2−x at 500°C in an atmosphere of pure hydrogen and further reduction, giving increased conductivity, occurs at elevated temperature. These films were comparable in quality to those prepared by more elaborate techniques.

Preparation and characterization of the quaternary chalcogenides Cu2B(II)C(IV)X4 [B(II) = Zn, Cd; C(IV) = Si, Ge; X = S, Se]

Abstract A number of quaternary chalcogenides crystallizing with the wurtz-stannite structure have been prepared by chemical vapor transport and characterized. Cu 2 ZnGeS 4 and Cu 2 ZnSiSe 4 transmit in the infrared beyond 12 microns. Cu 2 ZnGeS 4 was stable in air up to 620°C and also was the hardest of all the materials studied.

Concerning the role of oxygen in photocatalytic decomposition of salicylic acid in water

Abstract The photocatalyzed oxidation of salicylic acid on pure TiO 2 and ZnO films as well as on TiO 2 films loaded with various amounts of ZnO in N 2 O-saturated aqueous solutions has been investigated. It was found that the photoassisted decomposition of salicylic acid did not take place on the irradiated surface of pure TiO 2 and took place on ZnO when N 2 O was bubbled through the solution. The deposition of a small amount of ZnO onto the TiO 2 surface was responsible for the appearance of marked photocatalytic activity of material. The information about the electron-scavenger ability of N 2 O in interaction with TiO 2 has been obtained by conductivity and photoconductivity measurements. The main conclusion is that the major role of oxygen in photocatalytic oxidation of organic compounds is to be a scavenger for continuous electron removal from photocatalysts.

Preparation and characterization of thin films of alumina by metal-organic chemical vapor deposition

Abstract A simple novel horizontal reactor was used to prepare 2000 A films of alumina on silicon substrates by the thermal decomposition of aluminum tri-isopropoxide at temperatures between 350° and 500°C. The films were annealed in oxygen to test stability towards shrinkage and were characterized as to porosity, the presence of OH absorption bands in the infrared transmittance spectra and breakdown voltage.

Photoelectronic properties of ReS2 and ReSe2 single crystals

Abstract Large single crystals of ReS2 and ReSe2 were grown by chemical vapor transport and several of their properties were investigated. Both were found to ben-type semiconductors with resistivities in the range of 1–10 ohm-cm. Photoelectrochemical measurements in aqueous solutions ofI−3/I−resulted in high photocurrent densities, with ReSe2 being the more efficient photoelectrode. Analysis of their optical absorption spectra resulted in lowest-energy indirect optical band gaps of 1.32(5) eV for ReS2 and 1.17(5) eV for ReSe2. Photoelectrochemical spectral response measurements resulted in a measured lowest-energy indirect optical band gap of 1.4 eV for ReS2, which is in close agreement with that measured from optical absorption.