Surface Nanostructures Induced by Low Energy Ion Sputtering


Surface Nanostructures Induced by Low Energy Ion Sputtering

Facsko, S.; Keller, A.; Ranjan, M.; Möller, W.

Under special conditions low energy ion sputtering of solid surfaces leads to the formation of regular nanopatterns. These surfaces represent an interesting example of spontaneous pattern formation in nonequilibrium systems exhibiting different features like wavelength coarsening or a transition to spatiotemporal chaos. Different pattern types are observed for different experimental conditions, i.e. wavelike ripple patterns and hexagonally ordered dot arrays under oblique and normal ion incidence, respectively [1]. These patterns have gained increasing interest in recent years as templates for thin film growth. According to the model of Bradley and Harper (BH) [2], the regular patterns result from the competition between curvature dependent roughening and smoothing of the surface. Since the local erosion rate is higher in the valleys than on crests, the eroded surface is unstable. In the presence of smoothing mechanisms, however, a wave vector selection occurs and a periodic pattern with one spatial frequency is observed. The pattern formation can be described by continuum equations based on the BH model. Several extensions have been proposed in the last years, with the stochastic Kuramoto-Sivashinsky (KS) equation being the most prominent one [3]. However, although most experimental investigations on ion-induced pattern formation were performed under oblique ion incidence, only few theoretical studies focused on the corresponding anisotropic KS (aKS) equation. We will also present studies of thin film growth on these patterns. Depending on the interface energy of the metal film with the substrate the films grow in a conformal way reproducing the surface topography or as nanoparticles on the substrate surface. Furthermore, depending on deposition angle, substrate temperature, beam flux, and deposition time, the nanoparticles align parallel to the ripples, eventually coalescing and forming nanowires. Metal thin films grown in this way exhibit distinct optical properties due to their localized surface plasmon resonance. Because of the alignment these nanoparticles exhibit a strongly anisotropic plasmonic resonance [4]. In addition, the magnetic properties of ferromagnetic thin films grown on rippled surfaces are drastically change by the presence of the interface and surface periodic roughness [5].
[1] W. L. Chan and E. Chason, J. Appl. Phys. 101, 121301 (2007)
[2] R. Bradley and J. Harper, J. Vac. Sci. Technol. A 6, 2390 (1988)
[3] R. Cuerno and A.-L. Barabási, Phys. Rev. Lett. 74 4746 (1995)
[4] T.W.H. Oates, A. Keller, S. Facsko, et al., Plasmonics 2, 47 (2007).
[5] M. O. Liedke, B. Liedke, A. Keller, et al., Phys. Rev. B 75, 220407 (2007).

Keywords: ion beam sputtering; self-organized nanostructures

  • Invited lecture (Conferences)
    International Conference on Metallurgical Coatings and Thin Films, 26.-30.04.2010, San Diego, USA

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