Ion hammering eliminated as cause of elongation of embedded nanoparticles

Swift heavy-ion beams have long been wielded as an atomic-scale hammer, inducing deformation processes on scales ranging from macroscopic to submicroscopic. This century, swift heavy-ion irradiation has been envisioned as a versatile tool for tailoring the size, shape and alignment of nanoparticles embedded in a matrix, for example, for photonic devices with specified resonances. A new study in AIP Advances, departs from the view of many material scientists who consider the beams likely efficacious for the elongation and parallel orientation of ion-pummeled nanoparticles embedded in amorphous materials.

In their investigation of spherical zinc nanoparticles embedded in silica, Japanese scientists observed compaction and then ion hammering as the fluence of 50 MeV xenon ions increased a hundredfold, from when ion compaction prevails to when ion hammering dominates. The paper says that observations of nanoparticle behavior over the entire fluence range rule out both as drivers of resulting changes in shape and orientation.

The team followed how the zinc nanoparticles absorbed polarized light. The researchers concluded that changing absorption spectra indicated a linear, continuous elongation process, eliminating compaction and ion hammering as causes.

This finding, says lead author physicist Hiro Amekura, of Japan’s National Institute for Materials Science, delivers a blow to the synergy model that posits ion hammering with transient melting as driving the shaping process.

The team is now exploring other candidate models. Of key interest to Amekura is a model that attributes nanoparticle shaping to thermal pressure induced by heavy-ion irradiation.

Source: “Counterevidence to the ion hammering scenario as a driving force for the shape elongation of embedded nanoparticles,” by H. Amekura, N. Okubo, D. Tsuya, and N. Ishikawa, AIP Advances (2017). The article can be accessed at https://doi.org/10.1063/1.4993251 .