• R N Karekar

      Articles written in Pramana – Journal of Physics

    • Air-exposure effect on the resistivity of thin bismuth films

      S A Gangal R N Karekar

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      A survey of previous studies on vacuum deposited metal films shows that in high frequency measurements, explicit reference to the effect of air-exposure is not made. The present work on bismuth films (in-situ and air-exposed) at dc and rf frequencies, carried out mainly to study the air-exposure effect, shows that in-situdc and rf and exposed rf all show nearly the same resistivity for thick continuous films. But air-exposed dc film resistances, when compared to in-situdc resistances, show that the grain boundary reflection coefficient, Rgin Mayadas-Shatzkes model changes from 0·2 to 0·6. This is shown to be due to the grain boundary oxidation. The result is substantiated by rf measurements.

    • Effect of minute’s-scale aging on refractive index of chopped and non-chopped optical films

      R K Puri K Vijaya R N Karekar

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      The refractive indices of non-chopped and chopped films of cryolite, MgF2 and mixed cryolite-MgF2, which is higher than the bulk value, measured using spectro-photometer, ellipsometer and Abeles method are observed to be higher than corres-ponding bulk values. Chopped films show a higher refractive index than non-chopped films. The electron diffraction study shows a more amorphous structure for the chopped films. The major part played by chop-time seems to be in increasing the initial minute’s-scale aging rather than settling of ad-atoms during chop-time. The observed dispersion curve shows that some unknown material other than water gives an important aging effect.

    • Effects of various ambient-aging processes in chopped and non-chopped optical films

      K Vijaya R K Puri R N Karekar

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      The effects of various ambients on the non-chopped and chopped films of cryolite, MgF2 and mixed cryolite-MgF2, as measured by ellipsometer, are reported. The moisture decreases the refractive index whereas an increase is observed in air and other ambients. In all the ambient-aging the chopped films show smaller changes (nearly half) in refractive index than non-chopped films. Aging seems to be due to three main processes, a long-term adsorption-like surface reaction and two short-term reactions.

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