Counterevidence to the ion hammering scenario as a driving force for the shape elongation of embedded nanoparticles

Counterevidence is provided in the ion-hammering scenario as a driving force for the shape elongation of embedded nanoparticles (NPs) under swift heavy ion irradiation (SHII). Ion-induced compaction and the hammering, which are both induced in silica under SHII, dominate at low and high fluences, respectively, causing a crossover between them around a fluence of ∼4 × 1012 ions/cm2. Nevertheless, the shape elongation of NPs detected by the optical dichroism exhibits nearly linear dependence in a wide fluence range between ∼1 × 1011 and 2 × 1013 ions/cm2, indicating that the hammering does not play an important role.