Modification and Characterisation of Materials by Swift Heavy Ions

Swift heavy ions (SHI) available with 15 million Volt Pelletron accelerator at Inter University Accelerator Centre (IUAC) Delhi, formerly known as Nuclear Science Centre, (NSC), provide a unique opportunity to researchers for accelerator based materials science research. The major research areas can be broadly categorised as electronic sputtering, interface modifications, synthesis and modification of nanostructures, phase transitions and ion beam-induced epitaxial crystallisation. In, general, SHI irradiation based-materials may not be economically feasible, still it could be of interest for very specific cases in defence and space research. The paper gives a glimpse of the current research activities in materials science with SHIs, at IUAC.Defence Science Journal, 2009, 59(4), pp.401-412, DOI:http://dx.doi.org/10.14429/dsj.59.154

Swift Heavy Ion-induced Mixing

In this paper, the possible swift heavy ion (SHI)-matter interaction processes and their applicability to SHI-induced mixing have been discussed. The assumption that the SHI mixing is a consequence of a transient molten state diffusion has been brought forward. The following experimental evidences have been presented to verify the concepts developed for SHI mixing process: (i) Evidence of high temperature conditions in materials produced by SHIs via the study of SHI mixing in an Fe/Fe57/Si system; (ii) Verification of the hypothesis of transient molten state diffusion via a detailed study on Fe/Si system; (iii) The role played by a thermodynamical parameter, viz., interfacial free energy via a SHI mixing study on an Fe/Si multilayer; (iv) Demonstration of the occurrence of the process in an exclusively thermal-spike determined metal/metal system, viz., Fe/Ni multilayer; and (v) synthesis of technologically important SiC phases at room temperature via SHI mixing of C-allotrope/Si multilayers.Defence Science Journal, 2009, 59(4), pp.425-435, DOI:http://dx.doi.org/10.14429/dsj.59.154

Localized Surface Plasmon Resonance Studies on Pd/C Nano-Composite System: Effect of Metal Concentration and Annealing Temperature

The effects of metal concentration and annealing temperature on the localized surface plasmon resonance (LSPR) properties of the Pd nanoparticles (NP) dispersed in carbon were investigated. The Pd/C nano-composite thin films with 7 to 39 atomic % concentration of metal content were deposited using the atom beam co-sputtering techniques and subjected to annealing at temperature varying from 300 degrees C to 600 degrees C. The UV-vis spectroscopy studies on as-prepared films displayed a Mie scattering profile, but not well-defined LSPR bands were observed for all the values of Pd concentration. This is attributed to the smaller size (3-4 nm) of Pd NPs and rough Pd/C interface, as confirmed from TEM studies. When samples were annealed at a temperature of 300 degrees C, three broad LSPR absorption bands in the visible region, along with a sharp peak at 210 nm, were observed and the effect of Pd concentration variation was insignificant on their position. The multiple LSPR bands were observed due to agglomeration NPs, which is consistent with earlier reports and is also observed in the TEM images. When annealing temperature was subsequently increased to 500 degrees C, a blue shift in the LSPR peak position with an increase in the Pd concentration was observed, which phenomena is attributed to the formation of bigger NPs with the formation of sharp NPs-interface at high temperature upon annealing. A monotonic increase in the magnitude and decrease in the FWHM with an increase in concentration suggested change in the dielectric function of sample due to the growth of NPs. This is further confirmed from XRD studies, where strain relaxation and grain growth were observed. The intensity of the SPR peak decreased with an increase in the annealing temperature. The LSPR peak disappeared on annealing at a temperature of 600 degrees C, suggesting the formation of continuous polycrystalline thin films of Pd. In summary, NPs size, metal matrix interface, and concentration of metal play key roles in the tailoring the LSPR properties of the Pd

Shape deformation of embedded metal nanoparticles by swift heavy ion irradiation

an invited paper of SHIM 2008Swift heavy ions (SHI) induce high densities of electronic excitations in narrow cylindrical volumes around their path. These excitations have been used to manipulate the size and shape of noble metal nanoparticles embedded in silica matrix. Films containing noble metal nanoparticles were prepared by magnetron co-sputtering techniques. SHI irradiation of films resulted in the formation of prolate Ag nanoparticles with major axis along the ion beam direction. It has been observed that the nanoparticles smaller than the track size dissolve and other grow at their expense, while the nanoparticles larger than track size show deformation with major axis along the ion beam direction. The aspect ratio of elongated nanoparticles is found to be the function of electronic energy loss and ion fluence. Present report will focus on the role of size and volume fraction on the shape deformation of noble metal nanoparticles by electronic excitation induced by SHI irradiation. The detailed results concerning irradiation effects in silica-metal composites for dissolution, growth and shape deformation will be discussed in the framework of thermal spike model