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Description
The surface modifications induced by the impact of slow highly charged ions (HCI), in the form of nano-sized features such as hillocks, holes or craters, are influenced by various parameters, most notably the ion kinetic energy (velocity) and potential energy (charge state) [1]. Understanding the mechanisms underlying these surface modifications is crucial for applications in defect engineering, ion-beam processing, ion-beam analysis, and requires essential theoretical insights into the nanostructure formation process.
When slow highly charged ions impinge on a solid surface, they deposit their energy primarily into the electronic subsystem, leading to intense electronic excitation. This energy is subsequently transferred to the atomic subsystem via electron- phonon coupling, resulting in a transient increase in local energy density and a corresponding rise in lattice temperature within the impact region, which ultimately leads to surface modification.
The temperature evolution in metal surfaces irradiated with HCI has been investigated through the interplay between the two-step cohesive energy model [2] and an analytical thermal spike model [3]. The combined model indicates that the energy density associated with the velocity effect determines the type of nanostructure formed [4]. Hillocks are formed at lower ion velocities, where the energy density is lower, and craters emerge at higher velocities, where the energy density becomes significantly larger. The dependence of the temperature distribution profile on ion velocity and charge state has also been analyzed.
These results demonstrate that the coupled cohesive energy and analytical thermal spike framework provides valuable insight into the mechanisms governing velocity-dependent surface modification induced by slow highly charged ions.
[1] F. Aumayr et al., J. Phys.: Condens. Matter 23, 39 (2011)
[2] N. N. Nedeljković, M. D. Majkić, D. Banas, I. Stabrawa, Vacuum 224 113136 (2024)
[3] G. Szenes, Radiation Effects and Defects in Solids 175 (3-4) (2020) 241–256.
[4] M. D. Majkić, Material Science and Engineering: B, to be published