• M K Agarwal

      Articles written in Bulletin of Materials Science

    • Growth and characterisation of TaS2 single crystals

      M K Agarwal J V Patel H B Patel

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      Single crystals of tantalum disulphide have been grown by a sublimation or direct vapour transport method. Crystals as large as 15×10×0·05 mm3 grew in the form of platelets and needles above the charge which was kept well distributed within the ampoule. Characterisation of the as-grown crystals has been carried out at room temperature by x-ray diffraction. Electrical conductivity and magnetic susceptibility measurements have also been made.

    • Studies of defects in WSe2 single crystals

      M K Agarwal H B Patel T C Patel

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      A realistic estimation of growth and deformation fault probability has been made in the crystals of WSe2 grown by a direct vapour transport method. Electron microscopy of the specimens revealed the presence of two-fold ribbons from which theγ/μ ratio has been determined. Attempts to study polytypism have also been described.

    • 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.

    • Dislocation network patterns in tungstenite single crystals

      M K Agarwal K Nagi Reddy JV Patel N G Patel

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      TEM studies of tungstenite crystals grown by sublimation method have been investigated. Different types of dislocation network patterns were observed. The observed network patterns in bright field are compared with weak beam dark field pictures and the results are discussed.

    • 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.

    • Photoelectrochemical solar cell fabrication with tungsten diselenide single crystals

      M K Agarwal V V Rao V M Pathak

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      Recent reports on highly efficient photoelectrochemical solar cells withn-type WSe2 have prompted us to grown-type single crystals of WSe2 using a chemical vapour transport method. Different transporting agents have been used. It is seen that SeCl4 transporter leads to very large single crystals ofp-type WSe2, whereas the same transporting agent with excess amount of Se leads ton-type single crystals. PEC solar cells fabricated withp-type andn-type crystals thus grown have been reported and the results discussed.

    • Electrical properties of zirconium diselenide single crystals grown by iodine transport method

      S G Patel M K Agarwal N M Batra D Lakshminarayana

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      Single crystals of zirconium diselenide (ZrSe2) were grown by chemical vapour transport method using iodine as the transporting agent. The crystals were found to exhibit metallic behaviour in the temperature range 77–300 K and semiconducting nature in 300–443 K range. The measurements of thermoelectric power and conductivity enabled the determination of both carrier mobility and carrier concentration. The variation of carrier mobility and carrier concentration with temperature indicates the presence of deep trapping centres and their reduction with temperature in these crystals.

    • 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.

    • CVT growth of zirconium sulphoselenide single crystals

      S G Patel S K Arora M K Agarwal

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      Large single crystals of a few important members (x=0, 1, 2) of the series ZrSxSe2−x compounds have been obtained by chemical vapour (iodine) transport method. The crystals have been characterized for several properties. Their semiconducting nature is inferred from resistivity vs temperature measurements, their optical absorption data reveal indirect gap transitions, their thermoscans indicate their stability over a limited temperature range, and they essentially grow by the mechanism of two dimensional layer propagation.

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