Shape Elongation of Nanoparticles Induced by Swift Heavy Ion Irradiation

Abstract

In this chapter, the shape elongation of nanoparticles (NPs) induced by swift heavy ions (SHIs) and optical applications are described. SHIs are very high energy ions whose energy loss processes are dominated by electronic friction. To understand the elongation mechanism and the optical properties, Sect. 5.1 describes the fundamental phenomena induced by SHI irradiation, including the point defect production, ion track formation, ion-induced compaction, core/shell ion tracks, and ion hammering. In Sect. 5.2, the properties of the shape elongation are demonstrated with important concepts of the minimum width for the elongation, the mass non-conservation, the scaling law, etc. In Sect. 5.3, the elongation mechanism, while it is still in debate, is discussed comparing with the synergy model and the thermal pressure model, after introducing the concepts of the inelastic thermal spike, two-temperature molecular dynamics. Section 5.4 reviews the optical applications of the shape elongation, including the linear dichroism, the birefringence, possible application to nanometer-thick polarizer, the second-harmonic generation microscopy, etc. In Sect. 5.5, some comments are presented about the ion tracks, which are important to understand the irradiation effects with SHIs. Finally, the elongation by MeV C60 cluster ions is described in Sect. 5.6, which is as efficient as 200 MeV Xe ions, but two orders of the magnitude lower energy.