Abstract
Understanding material responses to energy deposition from energetic charged particles is important for defect engineering, ion-beam processing, ion-beam analysis and modification, geologic aging, space exploration, and nuclear applications. As an incident ion penetrates a solid, its energy is transferred to electrons and to atomic nuclei of the solid. Much of this electronic energy deposition is subsequently transferred to the atomic structure via electron–phonon (e–ph) coupling, leading to local inelastic thermal spikes in which energy dissipation is influenced by the local environment. In addition, intense ionization can lead to high densities of localized electronic excitations in wide-bandgap materials and ceramics that can affect defect dynamics and atomic mobility. Specifically, energy exchange between electrons and atomic nuclei, along with localized electronic excitations, can lead to substantial competitive (ionization-induced annealing), additive (both electronic and nuclear energy depositions contributing to damage production), and synergistic (more damage than the sums of separate damage processes) effects. Although nonmonotonic effects of the e–ph coupling strength and athermal processes are demonstrated for pre-existing defects and residual damage during ion–solid interactions, there is limited understanding of when such electronic effects must be considered in atomic-scale models of damage production and evolution in a broad variety of materials. Complex ceramics and chemically disordered solid solution alloys with different constituent elements allow a systematic evaluation of defect dynamics and irradiation performance with increasing complexity. Current knowledge regarding tuning of bonding characteristics and chemical disorder to control atomic-level dynamics is reviewed. Although a lack of fundamental understanding obstructs the advancement of reliable predictions for ion beam material modification, it highlights challenges and opens research opportunities. Insights into the complex electronic and atomic correlations with extreme energy deposition will strengthen our ability to design materials and predict ion-irradiation-induced damage in a radiation environment, and they may pave the way to better control fundamental processes and design new material functionalities for advanced technologies.
Highlights
Much of this electronic energy deposition is subsequently transferred to the atomic structure via electron–phonon (e–ph) coupling, leading to local inelastic thermal spikes in which energy dissipation is influenced by the local environment
This review describes the current understanding of the partitioning of electronic and nuclear energy depositions and subsequent coupled nonequilibrium processes and describes how to use ion beams to understand and control energy dissipation processes in order to tailor material functionality, create nanoscale phase transitions, and develop radiation-tolerant materials
While atomic displacements occur via ballistic-like elastic collisions, target electrons absorb a substantial portion of the incident ion energy through inelastic energy transfer, e.g., over 90% for ions with energies over 100 keV/amu and even over 99% for many light and medium ions
Summary
The irradiation of solids with energetic charged particles can lead to structural modifications and phase transformations that can dramatically alter the physical and chemical properties of the materials. Research focused on advancing the understanding of coupled defect evolution and recovery over a range of irradiation conditions is gaining momentum and is beginning to reveal the underlying mechanisms from intertwined ion-induced nonequilibrium processes
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