On the mechanism of the shape elongation of embedded nanoparticles

The mechanism of the shape elongation of metal nanoparticles (NPs) in silica, which is induced under swift heavy ion irradiation, is discussed with comparing the two candidates: (i) the synergy between the ion hammering and the transient melting of NPs by the inelastic thermal spike and (ii) the thermal pressure and flow model. We show that three experimental results are inconsistent with (i). The latter is supported by two-temperature molecular dynamics simulations, which simulate not only the atomic motions but also the local electron temperatures. A remarkable correlation was observed between the temporal evolution of the silica density around the ion trajectory and that of the aspect ratio of the NP later than ~ 1 ps after the ion impact, while no correlation was observed earlier than ~ 1 ps, even under the assumption of the instantaneous energy deposition.HA was supported by JSPS-KAKENHI Grant number 18K04898. IS, VJ, FD and KN gratefully acknowledge financial support from the Academy of Finland MESIOS and NANOIS projects, and CPU capacity grants from the IT Centre for Science CSC in Espoo, Finland. P.K. acknowledges the Australian Research Council for financial support