Edward A. Meyers

Conversion of chemically deposited photosensitive CdS thin films to n‐type by air annealing and ion exchange reaction

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 modificati...

Enhancement of photosensitivity in chemically deposited CdSe thin films by air annealing

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 a...

Interfacial diffusion of metal atoms during air annealing of chemically deposited ZnS-CuS and PbS-CuS thin films

The authors report on the interfacial diffusion of metal ions occurring during air annealing of multilayer CuS films (0.15-0.6[mu]m) deposited on thin coating of ZnS or PbS ([approximately]0.06 [mu]m) on glass substrates. All the films are deposited from chemical baths at room temperature. The interfacial diffusion on the metal atoms during the air annealing is illustrate by X-ray photoelectron spectroscopy studies. A multilayer of 0.3 [mu]m thick CuS film deposited over a thin film of ZnS upon annealing at 150 C shows atomic ratios of Zn to Cu of [approximately]0.15 and [approximately]0.48 at the surface layers of the samples annealed for 12 and 24 h, respectively. In the case of CuS on PbS film, the corresponding Pb to Cu atomic ratios at the surface layers are 0.43 and 0.83. The optical transmittance spectra and sheet resistance of these multilayer films indicate thermal stabilities superior to that of the CuS-only coatings. Application of the interfacial diffusion process in the production of thermally stable solar control coatings, solar absorber coating, or p-type films for solar cell structures is discussed.

Chemical deposition of Bi2S3 thin films on glass substrates pretreated with organosilanes

Abstract The chemical deposition of Bi 2 S 3 thin films on glass substrates modified by treatment with solutions of 3-mercaptopropyltrimethoxysilane and 3-aminopropyltrimethoxysilane is described. Such treatment helps prevent the peeling of thin films, a problem which is otherwise encountered in the chemical deposition process. Uniform thin films having thicknesses up to 0.32 μm were obtained on the modified surfaces. X-ray photoelectron spectroscopy was employed to demonstrate that silanization takes place at the surfaces of the glass substrates. The relative atomic concentrations of nitrogen or sulfur on these surfaces increase with the time of immersion in the silanizing solutions. X-ray diffraction patterns of air-annealed Bi 2 S 3 thin films were obtained. Optical transmittance and photoconductivity were measured and compared with those of the thin films deposited on untreated glass substrates. It was found that the thin films deposited on the silanized substrates were stable at 200 °C and maintain their original physical characteristics.

XRD, XPS, optical and electrical studies on the conversion of SnS thin films to SnO2

Abstract Results on thermal decomposition of chemically deposited SnS thin films to sub-stoichiometric and near-stoichiometric SnO 2 thin films on glass substrates are presented. The SnS-to-SnO 2 conversion is illustrated using X-ray diffraction spectra, X-ray photoelectron spectroscopy (XPS), optical transmittance spectra and electrical characteristics. SnS thin films of approximately 0.7 microm thickness and appearing deep red in transmission could be converted to transparent SnO 2− x films at temperatures above 325 °C. It requires about 20 h at 350 °C, 2 h 45 min at 400 °C. 30 min at 450 °C or 10 min at 500 °C for the near-complete conversion, but a relatively thinner film (of 0.25 microm) requires only about 30 min for the conversion at 400 °C. At the threshold of the transformation, the films show sheet resistance of about 10 4 ohms/□, which increases upon prolonged annealing to about 10 9 ohms/□ for 18 h annealing at 500 °C. The ratio of dark sheet resistance to photo sheet resistance is about ten for SnS films under 600 W m −2 tungsten-halogen light and is about 10 3 for SnO 2 films.

Modification of chemically deposited ZnSe thin films by ion exchange reaction with copper ions in solution

Abstract The modification of chemically deposited ZnSe thin films of ∼ 0.3 μm thickness by ion exchange in dilute solutions 0.001 M–0.025 M of CuCl2 has been investigated. The ion exchange reaction, as studied by XPS depth profile analysis, shows Cu/Zn ratios of 0.32 and 90 for a 90 s ion exchange in 0.001 M CuCl2 and a 3 min ion exchange in 0.01 M CuCl2, respectively. Following ion exchange, the binding energies are measured as 952 eV for Cu 2p 1 2 , 932 eV for Cu 2p 3 2 and 54.5 eV for Se 3d 5 2 . The corresponding values for CuSe thin film deposited directly from a chemical bath are 952, 932.5 and 55 eV. Optical transmittance spectra and sheet resistance measurements of the ion-exchanged films compare favourably with directly deposited CuSe thin films, which indicates the formation of CuSe. These results demonstrate that thin films of semiconducting materials can be prepared in a simple manner by ion exchange.

The crystal structure of di-n-butylarsinic acid

Abstract The crystal structure of di-n-butylarsinic acid has been determined from 1257 independent photographically recorded intensities. For convenience, a non-conventional triclinic cell, B 1 was chosen, a = 8.38(2), b = 13.12(3), c = 10.39(2) A, α = 91.5(5), β = 89.8(5), γ = 98.5(5)°, z = 4/cell, d(calcd.) = 1.31, d(measured) = 1.32 g/cc, R = 0.096 with unit weights, anisotropic temperature factors and no contribution of H-atoms included. The acid molecules are present as non-planar, H-bonded dimers across the centers of symmetry in the cell. The configuration around As is nearly tetrahedral, the average distance As-C = 1.95(2) A, As-O(1) = 1.67(1), As-O(2) = 1.74(1) A, O(1)-O′(2) = 2.47(2) A, and the dihedral angle between O(1)-As-O(2) and O(1)-O(2)-O′(1)-O′(2) is 140.0(7)° with a chair configuration for the dimer ring. The average distance C-C = 1.55(5) A, angle C-C-C = 110(2)°. The intra-dimer C-C contracts are ≧ 4.5 A, while there are a number of inter-dimer distances close to 4 A.

Bis(3-chloro-2-pyridyl) ditelluride

The entire ditelluride molecule is planar with an average deviation of its non-H atoms of 0.016 A. It is located on a center of symmetry at (1/2,0,0) with Te-TeA distance 2.725 (1) A and angle C(1)-Te-TeA 85.8 (1) o . Each half of the molecule consists of a substituted pyridine ring with average C-N distance 1.334 (6) A, C-C distance 1.38 (1) A and angle C-N-C 117. 5 (4) o . The ring is substituted in the 2-position [Te-C(1) distance 2. 121 (3) A] and in the 3-position [Cl-C(2) distance 1.736 (4) A]. All of these values appear to be normal and there are no abnormally short intermolecular distances present in the structure

THE CRYSTAL STRUCTURES OF 9,10-DICHALCOGENAANTHRACENES, C12H8XY, (X, Y) = (S, Se), (S, Te), (Se, Te), and (O, Se)

Abstract C12H8SSe and C12H8STe are monoclinic, P21/c, Z = 4/cell, isomorphous with C12H8S2 and C12H8Se2. C12H8SSe and C12H8STe are both disordered with unequal occupancies of the two chalcogen sites. Similarly, C12H8SeTe is disordered, orthorhombic Pbca, Z = 8/cell, isomorphous with C12H8Te2 and has unequal occupancies of its chalcogen sites. Because of the disorder, only average values of the molecular dimensions could be found. Within this limitation, bond angles and bond distances appear to be normal, as do the angles of fold in these butterflyshaped molecules. The crystals of of C12H8OSe were of poor quality, frequently twinned. The structure determined from the x-ray data is isomorphous with those of C12H8OS and C12H8OTe. The crystals are orthorhombic P212121.

Isolation and crystal structure of an unusual ditelluride: bis(N,N-dimethylaminoformyl) ditelluride

Abstract Solutions of disodium ditelluride in N,N-dimethylformamide (DMF) react with the solvent to give small yields of the unsual ditelluride, [Me2NC(O)]2Te2. This molecule, which exhibits interesting photochemical behavior has been characterized and its crystal structure has been determined.