Elongation of metallic nanoparticles at the interface of silicon dioxide and silicon nitride

In the process of shape transformation of metal nanoparticles (MNPs) embedded in dielectrics resulting from swift heavy-ion irradiation, key parameters such as the energy deposition threshold, the necessity of a molten track and the NP size have been identified for amorphous silicon dioxide. The extension of such parameters to other dielectrics is yet unclear. We present experimental evidence of the shape transformation of nearly spherical NPs located at the interface of amorphous silicon nitride and silicon dioxide thin layers upon irradiation with 185 MeV Au ions at fluences of 0.3 and 1 × 1014 cm−2. After irradiation the ∼16-18 nm diameter Au and Ag NPs transformed into continuous nano-rods exhibiting a high aspect ratio with a clear preference of elongation into the silicon dioxide layer. The results are discussed in the context of Thermal Spike calculations, which indicate that the track formation timescales may have an important influence on the NP elongation process.