Rayleigh-like instability in the ion-shaping of Au–Ag alloy nanoparticles embedded within asilica matrix

Abstract

We have studied how spherical23 ± 3 nmAu45Ag55 nanoparticles embedded within a silica matrix transform into prolate nanorods andnanowires by irradiating them with swift heavy ions. Samples were irradiated at roomtemperature and normal incidence with 74 MeV Kr and 36 MeV S ions for fluences up to1.0 × 1015 cm − 2. We demonstrate the existence of two regimes: (i) below a critical fluence, ∼ 2.0 × 1014 cm − 2, the transformation of the spherical nanoparticle into a nanorod is an individual process,i.e. each nanoparticle transforms into a single nanorod; (ii) for larger fluences thetransformation from nanorod to nanowire becomes a collective process, i.e. the break up anddissolution of unstable nanorods contribute to the growth of long nanowires. The passagefrom the first to the second regime can be interpreted in terms of a Rayleigh-like instabilityunder irradiation. The latter becomes active when the diameter of the nanowire approachesits saturation width under irradiation. Furthermore, we show that the composition of thealloy is only slightly modified during the ion-shaping process. Finally, the energyand the fluence thresholds for deformation and the deformation strain-rate areestimated.