Browsing by Author "Kanjilal, D."
Now showing 1 - 6 of 6
Results Per Page
Sort Options
Item Afm, stm and sts studies of grain boundaries And ion-beam induced defects in MGB2(Nova Science Publishers, 2001-06) Narayan, Himanshu; Narlikar, A. V.; Herrmann, P. S. P.; Samanta, S. B.; Gupta, Anurag; Kanjilal, D.; Muranaka, T.; Akimitsu, J.; Vijayaraghavan, R.Item 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.Item 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.Item SEM, STM/STS and heavy ion irradiation studies on magnesium diboride superconductor(Elsevier Ltd., 2002) Narayan, Himanshu; Samanta, S. B.; Gupta, Anurag; Narlikar, A. V.; Kishore, R.; Sood, K. N.; Kanjilal, D.; Muranaka, T.; Akimitsu, J.We have presented here the results of SEM and STM/STS investigations carried out on MgB2 superconductor. The SEM pictures show porous surface and well-linked granular structure in which bigger grains (few micrometer size) seem to be agglomeration of smaller, nearly hexagonal grains (size nearly 100 nm). Hexagonal structure of Mg and B layers have been directly observed in atomically resolved STM images. The lattice constants have been determined to be aMg ¼ 3:1 AA, aB ¼ 1:7 AA and c ¼ 3:5 AA. Grain boundaries (GB) of width ranging from 50 to 200 AA have been observed. Absence of weak link effects despite wide GBs has been attributed to the metallic nature of the amorphous region of the GB interior as inferred from STS analysis. Irradiation with 200 MeV 107Ag ions gives tracks of about 65 AA in the bulk of the sample. This is expected to give higher value of critical current density owing to the flux pinning mechanism, which is related to possibility of wide practical application of this material.Item Study of magnetization and pinning mechanisms in MgB2 thin film superconductors: effect of heavy ion irradiation(IOP Publishing Ltd, 2003) Narayan, Himanshu; Gupta, Anurag; Astill, D.; Kanjilal, D.; Ferdeghini, C.; Paranthaman, M.; Narlikar, A. V.We report magnetization studies on MgB2 superconducting thin films in a temperature range 4.2–40 K and magnetic field range 0–6 T. Thin films prepared by both pulsed laser deposition (PLD) and electron beam evaporation (EBE) methods were investigated. In addition, both films were studied before and after heavy ion irradiation by 200 MeV Ag ions with a dose of 1011 ions cm−2. Variation of sweep rates during the measurement of the magnetization loop reveals the presence of flux creep in both films. The PLD film, after irradiation, shows a severe degradation of Tc, critical current densities (Jc) in low fields and irreversibility line (B∗(T )). In contrast, the EBE film shows a slight enhancement in Tc, and nearly no change in Jc(B) and the position of irreversibility line after irradiation. For both pristine films, the obtained volume pinning forces Fp versus reduced field b = B/B∗ shows a good scaling for T 10 K, which matches well with the theoretical curve based on the flux line shear (FLS) pinning model. These and other results can be interpreted in terms of grain boundaries in MgB2 films acting as FLS channels.Item 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.