Fabrication of metallic nanostructures with ions: Theoretical concepts and applications

This Thesis has focused primarily on a novel understanding of the physical mechanisms responsible for the ion-induced bending phenomenon in metallic materials. Two distinct mechanisms were found to govern bending in 1. solid bulk and 2. nanoporous thin cantilevers.
The dense solid bulk case was shown to involve the formation and accumulation of a defect structure along the samples thickness. Since the observed cantilever curvatures were too large to be attributed to the volume change generated by isolated point defects, we postulated that bending involves the formation of highly mobile interstitial clusters which diffuse and combine to form sessile clusters in the regions beyond the ion implantation zone. This hypothesis was supported by the agreement of a rate-equation model with the experimental observations of two metals with distinct ion-induced bending behaviors, namely gold and aluminum.
A similar approach was attempted to explain ion-induced bending in cantilevers made of nanoporous gold. This revealed a series of particularities that led to the design of a model description taking into account the volumetric compaction of the irradiated zone rather than the diffusion of defect clusters. After reaching the optimal preparation method that allowed for reproducible bending, the experimental results could be satisfactorily described theoretically by assuming a non-monotonic dependence of the irradiated structure’s effective Young modulus on mean ligament size.