• S K Roy

      Articles written in Bulletin of Materials Science

    • Transistors made in laser recrystallized polysilicon on insulator films

      S Chandrasekhar P R Apte S K Roy

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      lpcvd polycrystalline silicon films were deposited on thermally oxidized silicon as well as onlpcvd silicon nitride deposited on silicon. Acw argon ion laser was used to recrystallize the polysilicon film into large grains (grain size from 5µm to 40µm). Boron was then implanted and standard N-channel silicon gate process and N-channel metal gate process were carried out to realisemosfets on this material. Channel mobilities upto 450 cm2/V-sec for electrons have been measured. This thin filmmosfet has a four-terminal structure with a top and a bottom gate and the influence of one gate on the drain current due to the other gate has been investigated. Comparison of theIDv-VD curves of the devices with physical models was found in good agreement.

    • Influence of non-stoichiometry of sulphides on adsorption isotherms of dyes

      D K Sengupta S K Roy S C Sircar

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      Depending on their non-stoichiometry, sulphides are classified as n-type or p-type semiconductors. Adsorption of dyes from aqueous and non-aqueous solutions has been made use of to study the surface characteristics of solid adsorbents. Their use in flotation as collectors or depressants is also reported. Adsorption of anionic tartrazine on CdS-doped Ag2S shows a lower value compared to undoped Ag2S. The dye adsorption characteristics on these sulphides has been explained on the basis of their defect-structures.

    • Laser chemical vapour deposition

      S K Roy

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      The special role of lasers in material processing is outlined in this article. In the background of the various chemical vapour deposition processes, the laser-induced chemical vapour deposition processes have been described. The unique aspects of pyrolytic and photolytic laser chemical vapour deposition have been stressed. Some of the recent experimental results on thin film deposition by laser have been reviewed. The problems and future of laser deposition processes have also been mentioned.

    • Properties of gallium arsenide and indium phosphide impatts at microwave and millimetre-wave frequencies

      S K Roy J P Banerjee

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      The static and high frequency properties of GaAs and InP impatts have been investigated for lower microwave and higher millimetre-wave frequencies using the computer simulation programmes developed by the authors. The profiles of negative resistance and reactance in the depletion layer of SDR and DDR devices based on GaAs and InP and their admittance properties have been investigated. The results indicate that InP impatts of the SDR and DDR varieties have higher drift zone voltage, higher negative resistance and higher negative conductance as compared to their GaAs counterparts, both in the microwave frequency and in the millimetre-wave frequency ranges. It is thus observed that higher radio-frequency power can be obtained from InP devices than from GaAs devices.

    • Self-propagating high-temperature synthesis of titanium borides

      S K Roy A Biswas S Banerjee

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      The application of self-propagating high-temperature synthesis (SHS) to prepare a few borides of titanium was investigated. Using the plane wave propagation mode, the synthesis of titanium borides in the cold-pressed cylindrical specimens of the component powder mixtures was effected and was studied as a function of boron content in the initial mix and the specimen size. SHS reaction in compacts having diam. of 6 mm or less and high bulk density could not be initiated and/or sustained and was considered to be a result of rapid heat dissipation.

    • Alumina ceramics by sol-gel technique

      S Ramanathan R Bhat D D Upadhyaya S K Roy

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      The processing of alumina ceramics using the sol-gel technique was investigated. Alumina sols were prepared by precipitation-peptization of aluminium hydroxide obtained from aluminium nitrate and aluminium oxyhydroxide obtained from aluminium isopropoxide. Sols cast on Teflon substrate were gelled by controlled dehydration at near-ambient temperature. Gels were converted to ceramics through processes of drying, calcination and sintering in the temperature range 773–1473 K. Ceramics derived from both the sols retained a porosity of 35–45% even after sintering at 1273 K. However, at 1473 K densification was drastically enhanced and bodies could be sintered to about 90–93% of theoretical density (TD) and was accompanied by theϑ-to-α transformation. The progress of the reactions occurring at various stages of the process was studied using pycnometry, TG-DSC, XRD, SEM, MIP and TEM techniques.

    • Studies on high temperature deformation behaviour of 3Y-TZP ceramics

      D D Upadhyaya S K Roy G K Dey S Banerjee

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      The present work reports the results on the deformation behaviour of ZrO2-3 mol% Y2O3 (3Y-TZP) ceramics which were prepared by pressureless sintering at 1400°C. Dense, cylindrical samples were subjected to uniaxial compression tests under a constant stress of 15 MPa in the temperature range of 1200–1400°C. The ceramics exhibit considerable ductility, attaining over 60% true strain without any edge cracking. Microstructural changes due to interaction of grain boundary viscous phase with the ultrafine and equiaxed grains were analyzed by transmission electron microscopy. Results show the grain boundary sliding accompanied by a diffusion accommodation process as the predominant deformation mechanism in these ceramics.

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