Ion-Nanoscale Matter Interactions

Abstract

Irradiation of spherical gold (Au) nanoparticles confined within a silica matrix with swift heavy ions induces their shaping into prolate nanorods along the beam direction. In this review, spherical colloidal Au nanoparticles with a diameter in the range of 15–30 nm (±3 nm) are irradiated at normal incidence with Ag ions with a kinetic energy in the range of 18–54 MeV to fluences between 1013 and 1015 ions/cm2 at 300 K. For example, under irradiation with 18 MeV Ag+4 ions to a fluence of 6.4 × 1014 ions/cm2, the originally spherical nanoparticles of 15 nm diameter are shaped into prolate nanorods with a length of 40 nm and a width of 8 nm. An aspect ratio of the major to the minor axis of the nanorods of about 5.0 ± 0.4 at constant volume is achieved. Saturation of the variation of the aspect ratio is reached at a fluence of 8.7 × 1014 ions/cm2. Irradiation of samples containing 15 nm Au particles with 25 and 54 MeV Ag ions has shown further lengthening of the Au nanorods, increasing with the increasing ion energy. Similar ion-shaping behavior is reported for 30 nm Au particles under irradiation with 18, 25, and 54 MeV Ag ion energies, respectively. By systematically monitoring the experimental data, we put in evidence the existence of a threshold fluence of Au nanoparticle elongation. The value of the threshold fluence is found to depend on both the ion energy and nanoparticle size.