Abstract
We investigate the ripple pattern formation on amorphous carbon surfaces at room temperature during low energy Ne ion irradiation as a function of the ion incidence angle. Monte Carlo simulations of the curvature coefficients applied to the Bradley-Harper and Cater-Vishnyakov models, including the recent extensions by Harrison-Bradley and Hofsäss predict that pattern formation on amorphous carbon thin films should be possible for low energy Ne ions from 250 eV up to 1500 eV. Moreover, simulations are able to explain the absence of pattern formation in certain cases. Our experimental results are compared with prediction using current linear theoretical models and applying the crater function formalism, as well as Monte Carlo simulations to calculate curvature coefficients using the SDTrimSP program. Calculations indicate that no patterns should be generated up to 45° incidence angle if the dynamic behavior of the thickness of the ion irradiated layer introduced by Hofsäss is taken into account, while pattern formation most pronounced from 50° for ion energy between 250 eV and 1500 eV, which are in good agreement with our experimental data.
Highlights
Low energy ion sputtering of solid elemental or compound surfaces at oblique ion incidence could produce a periodic self-forming nanostructure due to ion erosion and mass redistribution
An attractive theoretical approach to describe erosion as well as mass redistribution is the so called crater function formalism (CFF), which relies on molecular dynamic simulations
We have investigated the ripple pattern formation on amorphous carbon thin film due to Ne ion irradiation for a broad range of ion energies and ion incidence angles
Summary
Low energy ion sputtering of solid elemental or compound surfaces at oblique ion incidence could produce a periodic self-forming nanostructure due to ion erosion and mass redistribution. The CFF approach has the advantage that it solves the linear and non-linear theories without the assumption of simple models like Sigmund’s ellipsoidal energy deposition.[3,4,5,6,7,8] Recently Harrison and Bradley have shown that the crater function models used up to now are incomplete and must be extended to include the surface curvature dependence of the erosion crater function.[9] This curvature dependence is already accounted in the original Bradley-Harper model using Sigmund’s ellipsoidal energy deposition and contributes to the stabilization of the surface under ion irradiation for most ion incidence angles. For large angles of incidence this curvature dependence leads to a strong destabilizing contribution Another essential extension, which was neglected in the CV model[2] is that the height evolution of the surface of an irradiated layer is dependent of its thickness. Such a thickness dependent contribution to the equation of motion was recently introduced by Hofsass.[10,11] According to Hofsass, for an ion irradiated film, the layer thickness d at a given position depends on the ion incidence angle, which leads to
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