We investigate the ripple pattern formation on Si surfaces at room temperature during normal incidence ion beam erosion under simultaneous deposition of different metallic co-deposited surfactant atoms. The co-deposition of small amounts of metallic atoms, in particular Fe and Mo, is known to have a tremendous impact on the evolution of nanoscale surface patterns on Si. In previous work on ion erosion of Si during co-deposition of Fe atoms, we proposed that chemical interactions between Fe and Si atoms of the steady-state mixed Fe x Si surface layer formed during ion beam erosion is a dominant driving force for self-organized pattern formation. In particular, we provided experimental evidence for the formation of amorphous iron disilicide. To confirm and generalize such chemical effects on the pattern formation, in particular the tendency for phase separation, we have now irradiated Si surfaces with normal incidence 5 keV Xe ions under simultaneous gracing incidence co-deposition of Fe, Ni, Cu, Mo, W, Pt, and Au surfactant atoms. The selected metals in the two groups (Fe, Ni, Cu) and (W, Pt, Au) are very similar regarding their collision cascade behavior, but strongly differ regarding their tendency to silicide formation. We find pronounced ripple pattern formation only for those co deposited metals (Fe, Mo, Ni, W, and Pt), which are prone to the formation of mono and disilicides. In contrast, for Cu and Au co-deposition the surface remains very flat, even after irradiation at high ion fluence. Because of the very different behavior of Cu compared to Fe, Ni and Au compared to W, Pt, phase separation toward amorphous metal silicide phases is seen as the relevant pro-

A quantitative simulation of ion beam sputtering and related collision cascade effects is essential for applications of ion beam irradiation in thin film deposition, surface treatment and sculpting with focused ion beams, ion beam smoothing of surfaces and ion-induced nanopattern formation. The understanding of fundamental ion-solid interaction processes relevant for nanostructure formation, ion-induced mass redistribution, sputter yield amplification, ion beam mixing and dynamic compositional changes requires reliable simulations of ion-solid interaction processes in particular at low ion energies.In this contribution we discuss the possibilities, the key benefits and the limitations of three popular binary collision Monto Carlo simulation programs (SDTrimSP, TRIDYN and SRIM).The focus will be set to the calculation of angle dependent sputter yields, angular distribution of sputtered particles, sputter yields for compound materials, sputter yield amplification effects, as well as the extraction of parameters relevant for modelling ion-induced surface pattern formation from vacancy and recoil atom distributions.

The development of self-organized surface patterns on Si due to noble gas ion irradiation has been studied extensively in the past. In particular, Ar ions are commonly used and the pattern formation was analyzed as function of ion incidence angle, ion fluence, and ion energies between 250 eV and 140 keV. Very few results exist for the energy regime between 1.5 keV and 10 keV and it appears that pattern formation is completely absent for these ion energies. In this work, we present experimental data on pattern formation for Ar ion irradiation between 1 keV and 10 keV and ion incidence angles between 50° and 75°. We confirm the absence of patterns at least for ion fluences up to 1018 ions/cm2. Using the crater function formalism and Monte Carlo simulations, we calculate curvature coefficients of linear continuum models of pattern formation, taking into account contribution due to ion erosion and recoil redistribution. The calculations consider the recently introduced curvature dependence of the erosion crater function as well as the dynamic behavior of the thickness of the ion irradiated layer. Only when taking into account these additional contributions to the linear theory, our simulations clearly show that that pattern formation is strongly suppressed between about 1.5 keV and 10 keV, most pronounced at 3 keV. Furthermore, our simulations are now able to predict whether or not parallel oriented ripple patterns are formed, and in case of ripple formation the corresponding critical angles for the whole experimentally studied energies range between 250 eV and 140 keV.

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We report on the observation of the ion-induced hcp → fcc phase transition in 75 nm thick polycrystalline Co films, which were irradiated with 200 keV Xe ions to fluences of 2.5 × 10 13 -8 × 10 15 ions/cm 2 at a temperature of 300 K. Analyses by means of Rutherford Backscattering Spectroscopy (RBS), X-Ray Diffraction (XRD), Magneto-Optical Kerr Effect (MOKE) and Vibrating Sample Magnetometry (VSM) provided information on the film thickness and the implanted Xe profiles, the phase structure, the ion-induced lattice expansion and the magnetic hysteresis, respectively. After film deposition and irradiations up to 4 × 10 14 ions/cm 2 , we predominantly found the hcp phase (XRD, uniaxial MOKE pattern) with an in-plane magnetization. The transition to fourfold in-plane magnetization typical of the fcc-phase occurred around a fluence of 2 × 10 15 ions/cm 2 . We interpreted these findings as due to rapid cooling of thermal spikes into the metastable Co-fcc phase.