Flux dependent MeV self-ion-induced effects on Au nanostructures: dramatic masstransport and nanosilicide formation

Abstract

We report a direct observation of dramatic mass transport due to 1.5 MeVAu2+ ion impact on isolated Au nanostructures of average size≈7.6 nm andheight ≈6.9 nm that are deposited on Si(111) substrate under high flux(3.2 × 1010–6.3 × 1012 ions cm−2 s−1) conditions. The mass transport from nanostructures was found to extend up to a distanceof about 60 nm into the substrate, much beyond their size. This forward mass transport iscompared with the recoil implantation profiles using SRIM simulation. The observedanomalies with theory and simulations are discussed. At a given energy, the incident fluxplays a major role in mass transport and its redistribution. The mass transport isexplained on the basis of thermal effects and the creation of rapid diffusion pathsin the nanoscale regime during the course of ion irradiation. The unusual masstransport is found to be associated with the formation of gold silicide nano-alloys atsubsurfaces. The complexity of the ion–nanostructure interaction process is discussedwith a direct observation of melting (in the form of spherical fragments on thesurface) phenomena. Transmission electron microscopy, scanning transmissionelectron microscopy, and Rutherford backscattering spectroscopy methods have beenused.