• D N Bose

      Articles written in Bulletin of Materials Science

    • Measurement of magnetic properties of single crystal YIG by non-resonant method

      D N Bose S R Borgaonkar T S Vedavathy

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      A non-resonant microwave technique has been employed for the determination of saturation magnetisation (4πMs) andg-factor of pure and Gd-doped single crystal YIG spheres yielding accurate values. It was found that 4πMs=1720–1751 g for undoped and 1595 g for 10% Gd-doped YIG spheres whilegeff=2·00–2·0039. The advantages of this method are simplicity and complete absence of propagation corrections necessary in cavity resonance experiments.

    • Physics of silver halides and their applications

      D N Bose P A Govindacharyulu

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      Silver halides are notable for exhibiting both ionic and electronic conductivity which is responsible for their widespread use in photography. Due to differences in ionicity and bonding, their properties vary from the highly ionic silver fluoride to the more covalent silver iodide. These fundamental properties such as defect formation energies, carrier mobilities and band-structures, particularly of silver iodide, have only recently been determined. One interesting finding is the presence of high surface fields, caused by differences between interstitial and vacancy formation energies, which results in separation of photo-generated electron hole pairs. This throws new light on the photographic process and on the suitability of silver bromide as a photographic material.a-AgI is also the first fast ion conductor to be discovered. Structural instability, low defect formation energy and optimum cation size are responsible for this phenomenon but existing models fail to explain all the experimental results. Recent microwave conductivity and neutron scattering experiments which provide fresh insight are discussed.

    • Lithium solid electrolytes and their applications

      D N Bose D Majumdar

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      The preparation, characterisation and applications of two systems of lithium ion conductors, lithium zinc germanate (Lisicon) and lithium germanate vanadate are described. Ionic conductivity studies include ac conductivity, thermopower andnmr which provide complementary information. High pressure studies and fabrication of a solid-state cell are also reported.

    • CdTe photoelectrochemical solar cells—chemical modification of surfaces

      K C Mandal S Basu D N Bose

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      Chemical modification of bothn andp type CdTe has been found to improve the performance and stability of PEC solar cells. The surfaces, modified by Ru3+, have been examined by a variety of techniques. Modification results in enhanced barrier height at the surface due to the formation of a passivating oxide layer.

    • Foreword

      P Rama Rao D N Bose

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    • Photoluminescence and heavy doping effects in InP

      Seishu Bendapudi D N Bose

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      Photoluminescence (PL) studies on LPE-grown InP layers doped with selenium and having carrier concentrations from 1 × 1018 to 1 × 1020 cm−3 have been reported in this paper. Measurements at 300 and 77 K showed that the band to band recombination peak energy shifts to values as high as 1·7 eV with increasing doping, the increase being sharp beyond 4 × 1019 cm−3. These results have been explained as being the result of the Burstein shift and the band-gap shrinkage.

    • Effect of laser irradiation on the superconducting properties of high-Tc SmBa2Cu3Ox

      B K Roul A K Pradhan V V Rao P Bhattacharya P Pramanic V R Kalvey D N Bose K L Chopra

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      Studies of the effect of high power laser (Q-switched Ruby laser, 694 nm, 30 ns) irradiation on the critical current density (Jc) and magnetic hysteresis at 77K and temperature variation of microwave induced d.c. voltage on SmBa2Cu3Ox ceramic samples have been performed. Irradiation did not substantially changeTc but caused a strong increase inJc and magnetic hysteresis at 77K. The microwave-induced d.c. voltage at 77K showed appreciable decrease after irradiation. SEM studies showed grain growth due to sintering which improves the interconnectivity among the superconducting grains. These are attributed to physical densification and consequent reduction in the number of weak links. The increase of magnetic hysteresis after laser irradiation is presumably connected with the creation of defects which act as pinning centres. Thermal modelling suggests that on irradiation the surface melts up to a depth of 1µ and laser-induced evaporation occurs at energy density of 2·5 J/cm2.

    • Growth, characterization and electrical anisotropy in GaTe—a natural semiconducting superlattice

      S Pal D N Bose

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      GaTe is a III–VI semiconductor which has layered structure with large anisotropy in electrical properties. Growth of single crystals by the Bridgman technique permitted the measurement of thermoelectric power in orthogonal directions from which the anisotropy of hole effective masses were determined for the first time. From resistivity and Hall effect measurements the carrier activation energies and scattering mechanisms between 10–300°K were found.

      Study of the temperature dependence of conductivity revealed a variety of conduction mechanisms including weak localization below 20°K, hopping conduction between 20–50 K and band conduction in and across the layer planes atT>70 K. Weak localization was confirmed through observation of negative magnetoresistance. TheIV characteristics showed quantized behaviour due to tunneling across potential barriers, which may be due to stacking faults between layer planes as observed by TEM studies.

    • Lattice mismatch and surface morphology studies of InxGa1−xAs epilayers grown on GaAs substrates

      R Pal M Singh R Murlidharan S K Agarwal D Pal D N Bose

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      InxGa1−xAs (0·06≤x≤0·35) epilayers were grown on GaAs substrates by atmospheric pressure metal organic chemical vapour deposition technique. Surface morphology and lattice mismatch in the InGaAs/GaAs films of different compositions were studied. Cross-hatched patterns were observed on the surface of the epilayers for bulk alloy composition up tox≈0·25. Forx>0·3, a rough textured surface morphology was observed.

    • Transmission electron microscopy and X-ray diffraction studies of quantum wells

      D V Sridhara Rao K Muraleedharan G K Dey S K Halder G Bhagavannarayan P Banerji D Pal D N Bose

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      A series of InxGa1−xAs (x=0·47) quantum wells with InP barrier layers have been grown on InP substrates by metalorganic vapour phase epitaxy (MOVPE) at 625°C. The nominal well widths were defined during growth at (i) 25 Å, 39 Å, 78 Å and 150 Å for one sample and (ii) 78 Å for all 4 wells in another sample. The InP barrier widths have been kept constant at 150 Å. These layers have been characterized by X-ray diffraction (XRD) which from simulation gave the nominally 78 Å well width as 84 Å and the nominally 150 Å barrier width as 150·5 Å. Transmission electron microscopy (TEM) and high resolution TEM (HRTEM) have been carried out on etched and ion-milled samples for direct measurement of well and barrier widths. The well widths found from TEM are 25 Å, 40 Å, 75 Å and 150 Å. TEM micrographs revealed that, while the InP barrier layer is of good quality and the growth is confirmed to be epitaxial, dipoles are detected at the interface and the quantum well has some small disordered regions. These thickness measurements are in good agreement with earlier photoluminescence (PL) and secondary ion mass spectrometry (SIMS) studies.

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