Recently, elongation of spherical metal nanoparticles (NPs) and transformation to nanorods induced by swift heavy-ion (SHI) irradiation have been extensively studied. TEM observations indicate that the transformation requires the fluence higher than 10¹³ - 10¹⁴ ions/cm² even for ~100 MeV heavy-ions; i.e., overlaps of tens to hundreds of ion-tracks. 

Zinc NPs of 8 - 15 nm in diameter were prepared in silica by implantation of 60 keV Zn ions to 1.0 ´ 10¹⁷ Zn/cm². Then the NPs were irradiated by 200 MeV Xe¹⁴⁺ ions with an incident angle of 45 deg. At the fluence of 7 ´ 10¹¹ Xe/cm² where only 50% of the surface is covered by ion-tracks, weak but certain optical anisotropy due to the elongation of Zn NPs was detected by polarized light absorption spectroscopy. It was experimentally confirmed that only one impact of 200 MeV Xe ion induces the elongation of Zn NP. Comparison between the experimental absorption spectra and the calculated ones indicates that only one impact with 200 MeV Xe ion changes the aspect ratio of the NPs from 1.000 to 1.015 in average. Since it is known and was also confirmed in this system at higher fluence by TEM that only larger NPs than a threshold size show the elongation, the aspect-ratio change of the deformable NPs induced by one SHI impact is much larger than 1.5%.

Hiroshi Amekura*, National Institute for Materials Science, Japan
Norito Ishikawa, Japan Atomic Energy Agency (JAEA), Japan
Nariaki Okubo, Japan Atomic Energy Agency (JAEA), Japan
Mark C Ridgway, Australian National University, Australia
Raquel Giulian, Australian National University, Australia
Christoph Buchal, Forschungszentrum Juelich, Germany
Siegfried Mantl, Forschungszentrum Juelich, Germany
Naoki Kishimoto, National Institute for Materials Science, Japan

*presenting author