Interfaces under ion irradiation: Growth and taming of nanostructures

We have investigated the synthesis of nanostructures as well as the control of their size and location by means of ion beams. The phase separation and interface kinetics under ion irradiation give new possibilities to control the growth of nanostructures. Additionally, the chemical decomposition of the host matrix by collisional mixing may contribute to self-organization of nanostructures, especially at interfaces. It is shown how collisional mixing during ion implantation affects nanocrystal (NC) synthesis and how ion irradiation through NCs modifies their size and size distribution. An analytical expression for solute concentration around an ion-irradiated NC were found which may be written like the well-known Gibbs-Thomson relation. However, parameters have modified meanings which has a tremendous impact on the evolution of NC ensembles. Thus, inverse Ostwald ripening of NCs resulting in an unimodal NC size distribution is predicted, which has been confirmed experimentally for Au NCs in SiO2 and by kinetic lattice Monte-Carlo simulations. At interfaces, the same ion-irradiation induced mechanism may result in self-organization of NCs in a thin d-layer. Collisional decomposition of SiO2 may enhances the NC d-layer formation in SiO2 at the Si/SiO2 interface. The distance of the self-organized NC d-layer from the SiO2/Si interface makes it interesting for non-volatile memory applications.