• L K Malhotra

      Articles written in Bulletin of Materials Science

    • Photon, electron and ion beam induced physical and optical densification in chalcogenide films

      K L Chopra L K Malhotra K Solomon Harshavardhan S Rajagopalan

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      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 farir and Urbach tail studies reveal an enhanced strength of electron-phonon coupling, in obliquely deposited films having a very porous columnar microstructure, compared to normally deposited films. It has been shown that this enhanced electron phonon coupling is conducive to large thickness contraction and associated changes. These changes have been used in reprographic and lithographic applications. A correlation has been established between the thickness contraction and lithographic parameters. The possibility of generating both positive and negative relief patterns on the same film by controlling the etching time has been demonstrated.

    • Cobalt oxide-iron oxide selective coatings for high temperature applications

      C S Uma L K Malhotra K L Chopra

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      Cobalt oxide-iron oxide coatings on stainless steel have been prepared by spray pyrolysis technique. These coatings have absorptance (α) = 0·94 and emittance (ε100) = 0·20 which are much better values than for cobalt oxide or iron oxide alone on stainless steel substrates. The coatings have been found to be stable for temperatures upto 400°C.

    • Material science aspects of phase change optical recording

      L K Malhotra Y Sripathi G B Reddy

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      Chalcogenide thin films are used as the recording medium for phase change-type optical memory discs. The films are switched between amorphous and crystalline states using the heat of a focussed laser beam. Large reflectivity differences between amorphous and crystalline states are then used to store and retrieve the information. An active chalcogenide layer for this purpose should have a high optical absorption coefficient (α), and good structural and thermal stability. It should be possible to switch the chalcogenide layer between amorphous and crystalline states repeatedly within a short duration, the optical contrast should be high, and the material must have large cycling capability. Keeping the above requirements in mind, we have carried out systematic investigation of structural, optical and crystallization behaviour of thin films of various compositions of GaGeTe, Sb2Te3 and BiSe. These studies have shown that these materials can be good candidates for use as recording media in erasable phase-change optical recording.

    • Ellipsometric characterization of Cd1−xMnx Te thin films in the presence of perturbative fields

      Sharat Chandra L K Malhotra A C Rastogi

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      Ellipsometric studies in the 1·5 to 5 eV range have been carried out on thin films of Cd1−xMnx Te and exhibitE0,E1 andE11 transitions of the cubic semiconductors. The effect on these transitions upon irradiation by HeNe laser light, application of small alternating magnetic fields and the influence of both the fields, applied simultaneously, has been investigated. The observed critical point shifts have been interpreted on the basis of changes in the band structure of these thin films. This has been corroborated by theoretically calculating the effective number of electrons contributing to the transition per atom —Neff.

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