A method is presented for the deposition of CdS thin films of 0.05–0.7 μm thickness from solutions at 50–70 °C containing citratocadmium(II) complex ions and thiourea. The films show an optical band gap Eg≳2.6 eV. Optical transmittance is about 80% for photon energy <Eg. The dark conductivity of the films is of the order of 10−8 Ω−1 cm−1. The photosensitivity of these films is high, 106–107 under illumination with tungsten halogen light of 1 kW m−2. Annealing in air at 400–500 °C for 1 h converts the films to n type. It is possible to obtain sheet resistances of about 150 Ω for a 0.2 μm film (i.e., conductivity of 300 Ω−1 cm−1) by this process. Conversion of the films to n type is possible also by immersing the film in a 0.01 M HgCl2 solution for 15 min followed by air annealing for 1 h at 200 °C. The films show n-type dark conductivity of ≂0.05 Ω−1 cm−1 and photoconductivity of ≂1 Ω−1 cm−1. X-ray diffraction and x-ray photoelectron spectroscopic depth profile studies on the films show that the modification of the electrical characteristics is brought about through changes in composition of the surface layers in the films.

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Formation of the ternary compound Cu3BiS3 during annealing of chemically deposited CuS (∼0.3 μm) films on Bi2S3 film (∼0.1 μm on glass substrate) is reported. The interfacial atomic diffusion leading to the formation of the compound during the annealing is indicated in x-ray photoelectron depth profile spectra of the films. The formation of Cu3BiS3 (Wittichenite, JCPDS 9-488) is confirmed by the x-ray diffraction (XRD) patterns. The films are optically absorbing in the entire visible region (absorption coefficient 4 × 104 cm−1 at 2.48 eV or 0.50 μm) and are p-type with electrical conductivity of 102−103 Ω−1 cm−1. Potential applications of these films as optical coatings in the control of solar energy transmittance through glazings and as a p-type absorber film in solar cell structures are indicated.

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Organic arsenic compounds (trialkylarsines) present in natural gas were extracted by 10cm3 of concentrated nitric acid from 1 dm3 of gas kept at ambient pressure and temperature. The flask containing the gas and the acid was shaken for 1 h on a platform shaker set at the highest speed. The resulting solution was mixed with concentrated sulfuric acid and heated to convert all arsenic compounds to arsenate. Total arsenic was determined in the mineralized solutions by hydride generation. The arsenic concentrations in natural gas samples from a number of wells in several gas fields were in the range 0.01-63 pg As dmP3. Replicate determinations of arsenic in a gas sample with an arsenic concentration of 5.9 pg dm-3 had a relative standard deviation of 1.7%. Because of the high blank values, the lowest arsenic concentration that could be reliably determined was 5ngAsdmP3 gas. Analysis of nonmineralized extracts by hydride generation identified trimethylarsine as the major arsenic compound in natural gas. Low-temperature gas chromatography-mass spectrometry showed more directly than the hydride generation technique, that trimethylarsine accounts for 55-80% of the total arsenic in several gas samples. Dimethylethylarsine, methyldiethylarsine, and triethylarsine were also identified, in concentrations decreasing with increasing molecular mass of the arsines.

Improvement in photosensitivity, (σphoto−σdark)/σdark, of chemically deposited CdSe thin films on annealing in air is discussed. The as-prepared films of ∼0.5 μm thickness show photosensitivities of <10 under 600 W m−2 illumination. Upon annealing the films in air for 1 h each at various temperatures their photosensitivity increases depending on the temperature of annealing: ∼10 (200 °C), ∼102 (300 °C), ∼103 (400 °C), and ∼107 (450 °C). Air annealing at temperatures beyond 450 °C was found to cause degradation in the photosensitivity. The high photosensitivity is also accompanied by growth in photocurrent while maintaining a fast decay of ∼6 decades in <1 s after shutting off the illumination. Such a short decay time is unusual with chemically deposited photoconductive thin films. The results are explained on the basis of improvement in crystallinity and increase in chemisorption of oxygen upon annealing the films in air. X-ray-diffraction data and x-ray photoelectron spectroscopy depth profiling of the annealed films are presented in support of this explanation.

Good quality thin films of bismuth selenide of thickness up to 0.28 µm were deposited from solutions containing bismuth nitrate, triethanolamine and N ,N -dimethylselenourea maintained at temperatures ranging from room temperature to 40 • C. X-ray diffraction patterns of the samples annealed at 200 • C in air match the standard pattern of hexagonal Bi 2 Se 3 (paraguanajuatite, JCPDS 33-0214). The films exhibit strong optical absorption corresponding to a bandgap of about 1.7-1.41 eV in the as-prepared films. These values decrease to about 1.57-1.06 eV upon annealing the films at 200 • C for 1 h in nitrogen. As-deposited, the films show high sheet resistance (∼10 12 −1 ) in the dark. Annealing the films in air or in nitrogen enhances the dark current by about seven orders of magnitude; the resulting dark conductivity is about 10 −1 cm −1 . This enhancement in conductivity results from improved crystallinity as well as from partial loss of selenium.