Browsing by Author "Sharma, S. K."

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    A detailed investigation of surface modification in metallic glasses subjected to 130 MeV 28Si ion irradiation
    (2002-05) Narayan, Himanshu; Samanta, S. B.; Agrawal, H. M.; Kushwaha, R. P. S.; Gupta, Anurag; Sharma, S. K.; Narlikar, A.V.; Kanjilal, D.
    Surface modification induced in four metallic glasses by4.64 MeV/u 28Si ion irradiation has been investigated in detail using optical microscopy, SEM and STM. Results obtained in two separate runs have been presented here. The effects of ion fluence (/) and tilt angle (h) on surface modification have been studied both qualitativelyand quantitatively. It has been found that for Se values smaller than that for track formation, swift heavyion irradiation leads to smoothing of the irradiated surfaces. The smoothing is evident from decreasing mean roughness Rq and reduction in height of the hills and filling up of the valleys in the SEM and STM pictures. The observations have been explained on the basis of the theoryof shear flow within the framework of the viscoelastic model.
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    An SEM and STM investigation of surface smoothing in 130 MeV Si-irradiated metglass MG2705M
    (IOP Publishing Ltd, 1999) Narayan, Himanshu; Samanta, S. B.; Agrawal, H. M.; Kushwaha, R. P. S.; Kanjilal, D.; Sharma, S. K.; Narlikar, A. V.
    Metglass MG2705M foils of about 17 m thickness were irradiated at 90 K by 130 MeV 28Si ions, up to a fluence of 1:154 1016 ions cm−2. The surface modifications induced by irradiation have been examined by scanning electron microscopy (SEM) and scanning tunnelling microscopy (STM). It has been observed that smoothing of the sample surface is evident in both SEM and STM micrographs. The SEM pictures show a decrease in the heights of the ‘hills’ and filling up of the ‘valleys’ on micrometre length scales. The STM pictures, on the other hand, show smoothing of scratchlike surface disorders at nanometre length scales. However, the electronic energy loss Se, of 5:75 keV nm−1, does not lead to detectable track diameters, in agreement with the existing results. The observations have been attributed to a large electronic energy deposition due to high fluence, and a subsequent local shear relaxation of the near surface atoms. The theory of shear flow mechanism has been extended further to explain the results.
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    Surface smoothing of metallic glasses by swift heavy ion irradiation
    (Elsevier Ltd., 1999) Narayan, Himanshu; Agrawal, H. M.; Kushwaha, R. P. S.; Kanjilal, D.; Sharma, S. K.
    Self supporting samples of Metglass 2204 (Ti50Be40Zr10) and substrate bound samples of Metglass 2705M (Co69B12Si12Fe4Mo2Ni1) have been irradiated with 260 MeV 107Ag and 130 MeV 28Si ions, respectively at liquid nitrogen temperature. The surfaces have been examined by Scanning Electron Microscopy prior to and after irradiation. It is found that the surfaces have been smoothened after irradiation in both cases. The heights of the ÔhillsÕ have been decreased and the ÔvalleysÕ have been ®lled, without any detectable mass loss. The observed surface smoothing has been explained on the basis of shear ¯ow mechanism within the framework of the viscoelastic model. Ó 1999 Elsevier Science B.V. All rights reserved.