Nanoscale Shaping of Surfaces Using Slow Highly Charged IonsHYBRID

Upon impact on a surface, slow, highly charged ions can deposit several tens of keV within the very first layers of a material. This energy may trigger the emission of secondary particles (electrons, x-rays, sputtered target atoms) but can also lead to a permanent modification of the surface, e.g., craters or hillocks for bulk samples or pores in 2D materials. The susceptibility for highly charged ion-induced nano-structuring depends strongly on the material’s electronic response to strong electronic excitations and consequential electronic and structural relaxation processes, as well as the kinetic and potential energy of the projectile. Most studies, so far, focused on the modification of insulating or semiconducting surfaces, like CaF2 crystals, where thresholds regarding the ion potential energy were found: etch-pits and hillocks could only be observed on the surfaces when the potential energy exceeds a threshold value [1]. A similar behaviour was also discussed for free-standing MoS2 monolayers [2].
For metals, however, data regarding charge-state-dependent nanostructure formation is scarce, which is often explained by high charge carrier mobilities dissipating the deposited energy before atom displacement occurs. We could recently show that by reducing the sample size, i.e., going from a gold bulk sample to gold nano-islands, and thereby confining the potential energy within a small region, even the metal becomes susceptible to modification by highly charged ions [3].
Current experiments are limited by available ion charge states at low energies from lab-based ion sources. Here, HITRAP will allow us to explore so far uncharted territory at potential energies up to almost 1 MeV for fully stripped U ions to study the material under extreme conditions.

[1] A.S. El-Said et al. Phys. Rev. Lett. 109 117602 (2012)
[2] R. Kozubek et al. J. Phys. Chem. Lett. 10 904 (2019)
[3] G.L. Szabo et al. Small 2023 2207263 (2023)

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