Ion beam synthesis (IBS) and ion beam processing (IBP) have proved to be suitable methods to obtain materials based on NPs and to tune their properties. However, a general understanding of the behavior of nanostructures under irradiation is still lacking. For example, nanocomposite materials can be ion-driven into novel experimental configurations that are far off-equilibrium. In this regard, one longstanding and intriguing problem concerns the possibility of using ion-irradiation to inverse the thermodynamic stability of an ensemble of NPs. This means that, under thermodynamic conditons, larger particles grow at the expense of the smaller ones (Ostwald ripening-OR), whereas, under irradiation, smaller NPs become more stable than the larger ones. This process is called inverse Ostwald ripening (IOR).

Although several theoretical approaches have been developed in the past, only few experimental results exist in literature. However, experimental insights into the evolution of NPs under irradiation are obtained when a model system is used [1-3], i.e. chemically synthesized metallic NPs sandwiched between two silica layers. Thus, the IOR process is systematically investigated and all the parameters contained into the Heinig model are estimated, [4], i.e. the evolution of the capillarity length with temperature, the diffusivity under irradiation and the steady-state concentration for both planar and curved interfaces. We show that the Heinig model correctly describes the IOR process. However, the threshold temperature for the OR-to-IOR transition is not correctly defined and  two new intermediate regimes must be introduced. Finally, we redefine the concept of IOR showing that, depending on the steady state size, NPs under irradiation can either to grow or to be dissolved.

[1] G. Rizza et al Phys. Rev. B 76 (2007) 245414

[2] G. Rizza et al J. Appl. Phys. 101 (2007) 14321

[3] Y. Ramjauny et al. J. Appl. Phys. (2010)

[4] Y. Ramjauny et al. (to be submitted)