Rajdeep Kaur: Nanoscale Engineering with Ions: Formation of Nanostructures and Tuning of Material Properties

Abstract

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.