• P D Patel

      Articles written in Bulletin of Materials Science

    • Optical constants of WSe2 single crystals

      M K Agarwal P D Patel O Vijayan

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      The optical constantsn andk for WSe2 single crystals have been determined from the reflectivity measurements on basal plane of the crystal at wavelengths 5460, 4360 and 4050 Å. From the variation ofk with frequency of radiation, the optical energy band gapEo of the crystal has been evaluated.

    • Optical constants of MoxW1−xSe2 single crystal solid solutions

      M K Agarwal P D Patel O Vijayan

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      Single crystal solid solutions in the series MoxW1−xSe2 (0≤x≤1) have been studied by reflectivity measurements at oblique angles of incidence. The optical constants at a few wavelengths have been determined.

    • Electron microscopy of layered single crystals grown by direct vapour transport method

      M K Agarwal P D Patel J V Patel J D Kshatriya

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      Besides interesting properties such as optical, transport, structure, etc. possessed by crystals of transition metal dichalcogenides, they have also been found to have a potential application in the fabrication ofpec solar cells. These crystals are normally grown by carrier gas transport technique but are always contaminated by carrier gases. A new method of direct vapour transport has been developed and successfully applied to grow these crystals including those of off-stoichiometric varieties.

      The crystals thus grown have been characterized structurally using the techniques of x-ray powder, rotation and Weissenberg photographs and electron diffraction. Perfection studies have been made by techniques like chemical etching and electron microscopy.

      This review describes the electron microscopic studies made on the single crystals of the layered compounds. High resolution technique of weak beam has been employed to study dislocation pattern. Dissociated dislocations have been used to estimate stacking fault energy. Such measurements have also been carried out at different temperatures and the variation of stacking fault energy with temperature has been worked out. Interesting information regarding phase transformation for TaS2 and W3Se4 in the temperature range 109 to 580 K has been derived from the electron diffraction studies and the implications have been discussed.

    • Transport properties of MoSex Te2−x (0 ≤x ≤ 2) single crystals

      M K Agarwal P D Patel R M Joshi

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      The layer type MoSexTe2−x (0 ≤x ≤ 2) have been grown in single crystalline form by chemical vapour transport technique using bromine as the transporting agent. The electrical resistivity and Hall mobility perpendicular to thec-axis of the crystals were measured at room temperature. The variation of the Seeback coefficient with temperature was also investigated.

    • Growth and properties of CuInS2 thin films

      M K Agarwal P D Patel Sunil H Chaki D Lakshminarayana

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      Single phase copper indium disulphide (CuInS2) thin films of thickness between 60 nm and 650 nm with the chalcopyrite structure are obtained on NaCl and glass substrates by flash evaporation. The films were found to ben-type semiconducting. The influence of the substrate temperature on the crystallinity, conductivity, activation energy and optical band gap was studied. An improvement in the film properties could be achieved up to a substrate temperature of 523 K at a molybdenum source temperature of 1873 K.

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