Regensburg 2013 – wissenschaftliches Programm

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DS: Fachverband Dünne Schichten

DS 2: Focus Session: Ion Beam Induced Surface Patterns I

DS 2.3: Topical Talk

Montag, 11. März 2013, 10:30–11:00, H32

Interaction of energetic ultraheavy ions with surfaces — •Lothar Bischoff, Roman Böttger, and Karl-Heinz Heinig — Helmholtz-Zentrum Dresden-Rossendorf, Germany

Energetic ultraheavy polyatomic ions like Bi₃⁺⁺ and Bi₂⁺ produce very dense collision cascades in surface layers. Compared to monatomic ion impacts, which do not overlap in space and time within the heat relaxation time, the simultaneous impact of a few atoms in the same point can cause very different effects. Here, we report on FIB irradiation with fluences up to 10¹⁷ cm⁻² using a liquid metal ion source. Using ultraheavy ions, a significantly increased sputter yield of Ge has been found, which can be attributed to thermal processes. Another, more striking feature is the dramatic difference in the surface morphologies caused by monatomic and ultraheavy ion irradiation. For instance, the well-known spongy surface layer forms on Ge upon 20 keV Bi⁺ irradiation, whereas normal incidence Bi₃⁺⁺ irradiation with the same energy per atom results in hexagonally ordered dot pattern having an aspect ratio of about one. Similar pattern have been found on Si by ultraheavy ion irradiation, but only under substantial substrate heating. And, in hot Ge substrates, normal incidence monatomic Bi⁺ ions produce no longer Ge sponge but also dot pattern. A crude thermal analysis of the experiments shows that the considered dot pattern formation is associated with a critical energy density deposited by an ion close to the surface. A more comprehensive model on this pattern formation will be presented in a subsequent talk by K.-H. Heinig.
R. Böttger, L. Bischoff, K.-H. Heinig, et al. JVST B30 (2012)06FF12