We report on craters formed by individual 3 MeV=u Au q ini þ ions of selected incident charge states q ini penetrating thin layers of poly(methyl methacrylate). Holes and raised regions are formed around the region of the impact, with sizes that depend strongly and differently on q ini . Variation of q ini , of the film thickness and of the angle of incidence allows us to extract information about the depth of origin contributing to different crater features. DOI: 10.1103/PhysRevLett.101.167601 PACS numbers: 79.20.Rf, 61.80.Jh, 61.82.Pv, 81.16.Rf Energetic atomic [1-3], molecular or cluster ions [4] impacting solids may leave tiny holes at the surface often surrounded by a raised region of displaced material. The observed surface morphology [1][2][3][4] is similar to what is found in ablation craters produced by an intense laser pulse [5,6], in macroscopic craters produced by meteorite impacts on planets [7], or by balls dropped into granular media [8], although their spatial scales may differ by about 17 orders of magnitude. Depending on the energy regime of the ions and the type of material being bombarded, the shape of the impact features and the underlying mechanisms of formation may differ [9,10]. As the energy deposited by swift ions of equal kinetic energy, but different charge-states may vary substantially close to the surface, a detailed knowledge of charge-state dependent effects is of great importance for ion-beam based techniques of materials structuring (such as ion-track etching), particularly considering the new demands for smaller pattern sizes and the use of thinner layers [11]. Our results give direct evidence for a strong dependence of the surface modifications introduced by single fast ions on their charge state. For track-etching procedures, this means it is possible to control the etching sensitivity at the surface and charge equilibration below the surface should yield different etched shapes, dependent on the incident charge state. Moreover, by employing a series of well-defined nonequilibrium charge states, we could derive depth information on the near-surface effects induced by single fast ion impacts.In this Letter, we focus on cratering induced by high velocity ions. At specific kinetic energies of a few MeV per nucleon, such ions transfer more than 99% of their energy to the target-electron system. A considerable fraction of the energy deposited in the track of a swift heavy ion is concentrated in a core region ( % 1 nm), where ionizations are directly produced by the ions. Fast secondary electrons spread the rest of the energy over larger distances. The exact size of such regions depend on the material and on the velocity of the ions, while the total amount of energy loss per path length, S e ¼ dE e =dx, is well understood [12]. The subsequent electron dynamics, however, is a nonlinear phenomenon and it may result in large sputter yields and cratering, due to the coupling of electronic and atomic degrees of freedom [13][14][15]. For reviews on ion-induced electronic cratering pr...

We have investigated the irradiation induced interface mixing in ZnO/SiO2 (α-quartz) and Sb/Ni/Si thin layer systems under swift heavy ion irradiation in the electronic stopping power regime. The irradiations were carried out at 77 K using 100 MeV Ar, 260 MeV Kr, and 200 MeV Xe ions. For the ZnO/SiO2 system experiments were also carried out at lower ion energies (300, 600, and 900 keV, respectively) where nuclear stopping dominates. The alterations of the interface concentration profiles were determined by means of Rutherford backscattering spectrometry performed subsequently at the irradiated and the nonirradiated parts of the samples. While for the semimetal/metal Sb/Ni interface almost no mixing could be found after high-energy irradiation (mixing efficiency for Xe ions: k/Se<0.02 nm5/keV) the ceramic system ZnO/SiO2 strongly reacts upon high energy ion irradiation (Xe: k/Se=2.1 nm5/keV). The Ni/Si interface shows an intermediate effect (Xe: k/Se=0.2 nm5/keV). The mixing behavior found at high ion energies is in contrast to that found in the nuclear stopping regime, where Sb/Ni shows very strong mixing and phase formation while ZnO/SiO2 exhibits only weak ballistic mixing. As was previously observed for the formation of ion tracks, interface mixing due to electronic energy deposition also sets in only if the electronic stopping power exceeds a threshold value.

NiO single crystals and polycrystalline films of about 100nm thickness have been irradiated at liquid-nitrogen temperature with 90MeV Ar, 140MeV Kr, 230MeV Xe, and 350MeV Au ions. After bombardment with Xe or Au ions, transmission electron microscopy and small angle x-ray scattering reveal empty ion tracks with diameters between 2 and 4nm. These nanopores extend through the specimens and are terminated by spherical nanoparticles containing the material which is missing in the pores.

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