Swift heavy-ion irradiation of elemental metal nanoparticles (NPs) embedded in amorphous ${\mathrm{SiO}}_2$ induces a spherical to rodlike shape transformation with the direction of NP elongation aligned to that of the incident ion. Large, once-spherical NPs become progressively more rodlike while small NPs below a critical diameter do not elongate but dissolve in the matrix. We examine this shape transformation for ten metals under a common irradiation condition to achieve mechanistic insight into the transformation process. Subtle differences are apparent including the saturation of the elongated NP width at a minimum sustainable, metal-specific value. Elongated NPs of lesser width are unstable and subject to vaporization. Furthermore, we demonstrate the elongation process is governed by the formation of a molten ion-track in amorphous ${\mathrm{SiO}}_2$ such that upon saturation the elongated NP width never exceeds the molten ion-track diameter.

• Received 4 November 2010

DOI:https://doi.org/10.1103/PhysRevLett.106.095505