Ion-Induced Surface Patterns as Templates for Thin Film Growth

Nanostructured thin films are of growing relevance for all kind of applications in photovol-taics, plasmonics, or as magnetic materials. Various methods have been used to fabricate these nanostructured thin films with well defined morphology. Besides the top-down ap-proaches using lithographic methods, bottom-up, self-organized methods have been used ex-tensively in the last years because of their fast and easy way of producing patterns with struc-tures down to 10 nm.
Ion beam sputtering has proven to be a promising way to produce self-organized patterns on various surfaces. Depending on the ion incidence angle hexagonally ordered dot patterns as well as ripple patterns oriented perpendicular or parallel to the ion beam direction are formed during the continuous sputtering (see Fig. 1 left). These patterns are excellent templates for the growth of metal thin films. Depending on the interface energy of the metal film with the substrate the films grow in a conformal way reproducing the surface topography (Fig. 1 right top) or as nanoparticles on the substrate surface (Fig. 1 right bottom). Furthermore, depending on deposition angle, substrate temperature, beam flux, and deposition time, the nanoparticles align parallel to the ripples, eventually coalescing and forming nanowires [1].
Metal thin films grown in this way exhibit distinct optical properties due to their localized surface plasmon resonance. Especially for nanoscale optics aligned equidistant chains of metal nanoparticles are favoured. Because of alignment these nanoparticles exhibit a strongly anisotropic plasmonic resonance [2]. In addition, the magnetic properties of ferromagnetic thin films are drastically change by the presence of the interface and surface periodic roughness [3].

[1] T.W.H. Oates, A. Keller, S. Noda, et al., Appl. Phys. Lett. 93 (2008).
[2] T.W.H. Oates, A. Keller, S. Facsko, et al., Plasmonics 2, 47 (2007).
[3] M. O. Liedke, B. Liedke, A. Keller, et al., Phys. Rev. B 75, 220407 (2007).