Previous works have shown that silica-embedded Ge nanoparticles (NPs) of different sizes irradiated with swift heavy ions (SHI) at the same energy may elongate along the incident ion direction, perpendicular to it, or not at all. Here, for a given NP size distribution, we investigate the SHI energy dependence of the elongation process. Higher energy irradiation generally yields elongation along the ion track (as previously observed for similar NP size/SHI energy), but for lower energy irradiation elongation both parallel and perpendicular to the ion direction was observed. This demonstrates that NP size and electronic energy loss together govern the elongation process, reinforcing the proposed model where elongation perpendicular to the ion direction is only expected for Ge NPs bigger (before irradiation) than the mean ion track diameter in silica. Furthermore, our XAS measurements enable the first quantification of crystalline, amorphous and oxidized environments around Ge atoms. Combining such results with TEM observations shows the Ge NPs are rendered amorphous prior to elongation, potentially via a melt-and-quench process. Thereafter, stronger electron-phonon coupling in amorphous Ge compared to crystalline Ge may potentially influence the elongation process. The Ge NP amorphisation occurs at lower fluences for higher irradiation energies, indicating electronic energy loss – and not ballistic effects – governs the amorphisation. Subsequent to amorphisation and elongation, TEM and XAS results also show the NPs gradually intermix with SiO₂ and dissolve within the matrix as the irradiation fluence increases.

Leandro Langie Araujo*, The Australian National University, Australia
Raquel Giulian, The Australian National University, Australia
David J Sprouster, The Australian National University, Australia
Claudia S Schnohr, Friedrich-Schiller-Universität Jena, Germany
David J Llewellyn, The Australian National University, Australia
Bernt Johannessen, Australian Synchrotron, Australia
Aidan P Byrne, The Australian National University, Australia
Mark C Ridgway, The Australian National University, Australia

*presenting author