K L Chopra
Articles written in Bulletin of Materials Science
Volume 4 Issue 5 December 1982 pp 549-561 Research Report
Rapid solidification of metallic melts at a rate ≳105 °K/sec has gained considerable interest for casting non-equlibrium crystalline structures in general and metallic glasses in particular. Of the variety of techniques used for rapid solidification, melt-spinning and melt-extraction are widely used. This paper describes the design and development of a melt-spinning technique in our laboratory. Optimization of spinning parameters for smooth and continuous ribbons is discussed. Glassy ribhons of Cu-Zr and Pd-Ge alloys have been made under optimized conditions. A brief account of some of the structural and electronic properties of these glasses is illustrated.
Volume 6 Issue 6 December 1984 pp 1013-1018
Irradiation of 80° deposited Se-Ge films with band gap photons, 8 keV electrons and 50 keV He+ ions produces, primarily irreversible red shift of the absorption edge and major changes in doping and electrochemical adsorption processes. These changes have been attributed predominantly to the radiation-induced thickness and hence volume contraction resulting due to the physical collapse of the low density columnar microstructure of the obliquely deposited films. The far
Volume 8 Issue 3 June 1986 pp 285-289
Heterojunctions of hydrogenated a-Si films prepared by r.f. sputtering with spraypyrolyzed CuInS2 films have been studied. Capacitance-voltage measurements establish the formation of abrupt heterojunction. The barrier height varies from 0·26 to 0·55 V as the resistivity of CuInS2 film decrease from 1·5 × 103 to 65 Θm. These junctions exhibit photovoltaic behaviour with
Volume 8 Issue 3 June 1986 pp 291-296
Flash-evaporated technique has been developed for deposition of CuInSe2 thin films. A control over the stoichiometry and chemical composition of the films has been obtained by varying the deposition parameters. Single phase chalcopyrite structure films with optical gap ∼ 1·15 eV have been obtained. The electronic properties of the films have been tailored for solar cell applications.
Volume 8 Issue 3 June 1986 pp 379-384
Thin films of tungsten carbide have been deposited on stainless steel substrates held at 500°C by r.f. reactive magnetron sputtering in two different modes of introducing argon and acetylene gases called normal and high rate mode. A single phase fcc-WC is formed in the normal mode whereas a mixture of A-15-W3C, hexagonal-WC and graphitic- and diamond-carbon is found in the high rate mode. A microhardness value as high as 3200 kgf/mm2 (as compared to the bulk value of 1800 kgf/mm2) is obtained in the film deposited by normal mode.
Volume 8 Issue 3 June 1986 pp 385-389
Cobalt oxide-iron oxide coatings on stainless steel have been prepared by spray pyrolysis technique. These coatings have absorptance (
Volume 9 Issue 3 August 1987 pp 169-180
The effect of composition, sintering parameters, frequency and temperature on the dielectric parameters of ZnO-based ceramic semiconductors (cersems) having small amounts of Bi2O3, Sb2O3, CoO, MnO2, La2O3 and/or Cr2O3 has been investigated. The unusually high dielectric constant of these composites, arising due to a two-phase microstructure has been explained on the basis of a depletion layer model. The agreement in values of barrier height and donor concentration calculated from
Volume 14 Issue 2 April 1991 pp 217-222 International Conference On Superconductivity—I
The role of preparation conditions and the effect of addition of Pb in Bi-Sr-Ca-Cu-O (BSCCO) superconductor, on the
Volume 14 Issue 3 June 1991 pp 713-718 International Conference On Superconductivity—II
Studies of the effect of high power laser (Q-switched Ruby laser, 694 nm, 30 ns) irradiation on the critical current density (
Volume 17 Issue 6 November 1994 pp 841-848
Volume 18 Issue 6 October 1995 pp 639-668
The black art of thin films exhibiting whimsical properties and thus called ‘the fourth state of matter’ enticed the author to a challenge to unravel the mysteries of matter created
Volume 19 Issue 2 April 1996 pp 411-416
Surface structure of thin silver films (200 Å) on two technologically important films, indium tin oxide (ITO) and aluminium oxide, has been studied using scanning tunneling microscope. ITO films were prepared by reactive electron beam evaporation. Aluminium oxide films were prepared by oxidizing 2000 Å thick aluminium films evaporated on to H2 terminated single crystal silicon substrates. The surface structure of silver on ITO and aluminium oxide appeared to be same and was characteristic of Stranski-Krastanov type. The observed asymmetry in the island shape was attributed to the anisotropic nature of the strain fields surrounding the nucleation centres.
Volume 19 Issue 2 April 1996 pp 417-422
The presence of different kinds of surface lattice defects such as missing atom, interstitial atom, line defects, in graphite single crystal have been identified by using scanning tunneling microscope. These defects cause displacement of atoms from their mean position and lattice strain is introduced. By measuring the displacement of atoms from their mean position. lattice strain has been calculated. It is found that among single point defects, vacancies cause maximum lattice strain.
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