• S Rama Swamy

      Articles written in Proceedings – Section A

    • The scattering of light by thin metallic films

      S Rama Swamy

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      Observations on a new kind of light scattering shown by thin films of metals obtained by evaporation in vacuo and cathodic sputtering are described. The light scattered by such films exhibits anomalous depolarisation characteristic of metallic surfaces. It is thus essentially a surface effect and not the ordinary Rayleigh type of colloidal scattering. The portions of the film which are thin enough to show this effect are found to have no metallic reflection and either a large or else a practically infinite electrical resistance. It is suggested that the metallic film has three possible different states: a crystalline state with metallic properties, a two-dimensional gaseous state which is not metallic and is non-conducting, and thirdly an intermediate state with high electrical resistance. An evaporated silver film in the first state scatters little light and is black by scattered light. In the intermediate state, it scatters bright orange yellow light, and in the gaseous state, a bright green. Observations on the colours of the film by transmission and reflection examined with a nicol are also recorded. It is hoped that a more detailed quantitative investigation of the scattering of light by thin films of metals will throw light on their nature.

    • X-ray analysis of the structure of iridescent shells

      S Rama Swamy

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      X-ray diffraction patterns of the nacreous layer of iridescent shells have been obtained using a monochromatic X-ray beam incident along various directions. From a study of these patterns it is found that the nacreous layers of all the shells consist of aragonite crystals orientated with theirc axes normal to the surface. But the orientations of the other two axes vary with the particular kind of shell examined. For instance, theab plane is randomly orientated inTrochus andTurbo. InNautilus evidence for twinning is found combined with a specific orientation of theab plane. Theab planes of the crystals inMytilus viridis andMargaratifera vulgaris are found to exhibit specific orientation with respect to the lines of growth. The error in orientation is also much smaller than inNautilus pompilius. The results obtained closely correspond with the optical observations of Sir C. V. Raman.

    • X-ray analysis of the structure of iridescent shells - Part II.—TheHaliotidœ.

      S Rama Swamy

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      X-ray diffraction patterns, obtained with monochromatic X-rays, of some species ofHaliotis shells have been studied. It is found that the patterns given by these shells with normally incident X-rays are somehwat different to what has been previously obtained withTurbo andTrochus. In the latter shells there is random orientation of thea andb axes of aragonite crystallites. But inHaliotis species instead of random orientation of this type there is preferred orientation of thea andb axes with a large error in orientation. Thec axis is normal to the laminations as in all the other aragonite shells examined previously. Patterns obtained withNautilus pompilius andM. vulgaris have been measured and the Bragg planes causing the various reflections identified. From these measurements, the type of orientiation of twin crystals of aragonite suggested forNautilus in the author’s previous paper is confirmed. Also the necreous layer ofM. vulgaris is found to consist of single crystals of aragonite with their 110 planes parallel to the lines of growth, and thec axis normal to the shell surface.

    • The structure of thin metallic films

      S Rama Swamy

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    • Effect of heat on the structure of single crystals of silver amalgam

      S Rama Swamy D S Sake Gowda

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      Single crystals of theγ-phase of the system Ag-Hg have been grown from a globule of mercury immersed in a suitable solution of silver nitrate. The effect of heat on these crystals has been studied by taking X-ray diffraction patterns. It is found that on heating the crystals, the single crystal rotation pattern develops diffuse rings of a powder pattern. On further heating, these rings develop into a sharp complete powder pattern while the rotation pattern disappears. Results are explained as due to the faulting “domains” in the crystal growing bigger and bigger. On heating further, the domains grow into randomly orientated crystallites at the expense of the original lattice. It is likely that crystallites may develop into theβ-phase amalgam at temperatures beyond about 80° C. and retransform to theγ-phase on cooling.

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