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Abstract: Swift heavy ions have unique feature of creating ion tracks in insulators of dimension from a few nm to about 10nm. This particular feature of the swift heavy ions is used to engineer the size and shape of the nanoparticles embedded in silica matrix. On the basis of several experiments, it is evidenced that the embedded nanoparticles either grow in size or reduce in size, if they are smaller than or comparable to the ion track size. The shape transformation from spherical to elongated along the beam direction occurs, when the nanoparticle size is larger than the ion track diameter in silica. The reduction, growth and elongation of Au nanoparticles embedded in silica matrix under swift heavy ion irradiation have been discussed in the frame work of thermal spike model. [ABSTRACT FROM AUTHOR]

Abstract: Ions with energies larger than 100 keV/amu produce high densities of electronic excitations in narrow cylindrical volumes around their path. The perturbation of the electronic system is transferred to the atomic network, leading to structural transformations such as the nucleation of metal particles in glasses and to changes in the particle size, shape or spatial distribution in nanocomposites. Results of our group concerning irradiation effects in silica-metal composites are discussed in terms of thermal spikes and hammering mechanisms. [Copyright &y& Elsevier]

We report, an optical characterisation by spectroscopic ellipsometry of cobalt (Co) nanocrystals embedded into SiO2 matrix. Co clusters have been formed into a 250 nm thick thermal SiO2 layer on Si substrate during Co+ ion implantation at an energy of 160 keV and at fluences of 1017 ions/cm2 at different temperatures of 77, 295 and 873 K. The obtained nanocrystals have a size range of 2 to 10 nm. Spectroscopic ellipsometry measurements are performed in the 350 to 850 nm spectral range. Experimental data are analysed and interpreted in terms of both nanostructures distribution with depth into the sample and optical properties of the Co nanostructures. We have used a multi-layers model where volume fractions and complex optical constants of nanostructures have been varied. Layers of this model are considered as mixture of Co clusters and silica according to Maxwell-Garnett effective medium theory. Differences between optical constants of bulk and nanostructured cobalt have been observed. [Copyright &y& Elsevier]

Cobalt ions have been implanted at an energy of 160 keV at fluences of 2×1016, 5×1016 and 1017 Co+ cm−2 in silica layers and at temperatures of 77, 295 and 873 K. The nanocomposites formed have further been irradiated with electrons and swift heavy ions. Magnetic properties of the nanoparticles studied by a SQUID magnetometer at 295 and 5 K have been related to the modification of particle size and size distribution, which have been observed by transmission electron microscopy. [Copyright &y& Elsevier]