**7. Future directions**

**65** Clearly, the response of both freestanding and embedded gold nanoparticles is drastically different than gold in bulk or thin-film morphologies and is highly dependent on the radiation environment, particle morphology, and surface conditions. Additional work is needed to elucidate the underlying physics governing the increased sputtering and other scaling effects observed in gold nanoparticles [26, 27, 56]. Without a detailed understanding of the mechanisms active when the displacement damage length scale of the radiation event approaches that of the size of the nanoparticle exposed, it will be challenging to employ gold nanoparticles in most radiation environments. If the significant enhancement of sputtering is inherent and cannot be overcome, then the application of gold nanoparticles subject to ionizing radiation may be limited to those environments that produce minimal dose or sputtering yields. Conversely, if properly understood and controlled, the enhanced sputtering yields may also open new fields of study and possible

applications utilizing the rapid degradation or the satellite morphology in the irradiated embedded nanoparticles seen in **Figure 8** [23, 61]. If not, the field may explore the response of other types of nanoparticles and nanostructured materials for inclusion in the next generation of devices that must withstand complex radiation environments. To be able to understand the effects of enhanced sputtering, systematic and thorough experimental and modeling efforts are needed along the lines of those presented in **Figure 6** [59].
