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Beams of energetic ions can be used for material analysis and modification. It provides us with a tool featuring unique control over the area, depth and amount of damage in the material. This property of ion beams can be used to generate desired changes in material properties or form nanostructures with specific characteristics in the material. While the modification of materials through the irradiation of GeV energy ions has been extensively researched, it is worth considering MeV ion irradiation for ion beam-based material modification. Accelerators with the ability to deliver ions in the MeV energy regime, such as tandem accelerators with a few MV terminal voltage and cyclotrons, are more accessible, easier to maintain and already available in industrial spaces. Thus, a comprehensive study on whether the damage caused in different material systems by MeV ion irradiation can be used for nanostructure engineering needs to be performed. In this thesis, the formation of nanostructures by MeV ion irradiation in two different materials is studied. The dependence of the nanostructures formed on the ion parameters such as ion type and energy is investigated for two material systems. In the first study, we investigate the formation of nanostructures on the surface of a model system, i.e., single crystals of CaF₂. In the second study, we investigate the formation of etchable ion tracks in polyimide membranes. Nanoscale pores and channels, that can be formed from these etchable ion tracks, are expected to be the basis of next-generation detectors, biosensors and DNA/RNA sequencing. In the case of both materials, three distinct regions of ion-induced damage are identified after irradiation. The thresholds dividing these distinct regions of damage are dependent on ion velocity. Thus, electronic stopping power thresholds for the formation of nanostructures in materials are observed to be lower for MeV ions than for GeV ions.

Understanding ion-matter interactions is fundamental to advancing nanoscale engineering using ions. This thesis presents a comprehensive investigation into energy deposition by energetic ions across the keV-MeV energy regime and its correlation to observable changes in the structural and material properties. By expanding the investigation across different material systems, viz., crystalline, polymeric and amorphous, this thesis provides a unified perspective on energy transfer processes and, at the same time, illustrates how they can be utilised to modify material properties.  

The first section of the thesis focuses on the nanoscale structural modification induced by MeV ions. The impact of energy deposition, in the MeV energy regime, on the formation of surface nanostructures in single-crystal CaF₂ and nanoscale ion tracks in polyimide foils is investigated. In polyimide foils, the effect of the evolution of the ion charge state on energy deposition, and consequently on ion track formation, is studied. Extending this approach, amorphous TiO₂ films are investigated under separate and sequential irradiation by MeV ions and keV electrons. This analysis across different materials provides a broader understanding of the relationship between energy transfer processes and structural modifications.  

The second section of the thesis focuses on understanding how keV ion implantation can be used to introduce controlled local structural modifications in Pd/TiO₂/Pd memristors to tune their functional properties. The ion-induced structural modifications are correlated with variations in resistive switching properties. Complementary ¹⁸O isotope tracing with nuclear reaction analysis is used to probe atomic migration under applied voltage in ion-implanted memristors, revealing how ion-induced modifications influence atomic migration, which in turn governs the switching mechanisms.

Overall, this thesis demonstrates that energetic ions can systematically induce modifications across material systems and energy regimes. By correlating energy deposition with observed material modifications, the thesis provides a coherent framework for understanding how fundamental ion-matter interactions lead to structural changes and influence the material properties. These insights provide a general perspective on employing energetic ions as a potential tool for nanoscale engineering, ranging from the formation of nanostructures to the tuning of material properties.