Abstract:
“Surface Nanostructures Induced by Low Energy Ion Sputtering”
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 non-equilibrium 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. These patterns have gained increasing interest in recent years as templates for thin film growth. According to the model of Bradley and Harper (BH), 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. 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. 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.

Brief Bio:
Dr. Stefan Facsko has been the Leader of the Junior Research Group “Low Energy and Highly Charged Ions” in the "Nanostructures" Department within the  Institute of Ion Beam Physics and Materials Research, Forschungszentrum Dresden-Rossendorf e.V. Bautzner Landstr. 400, 01328 Dresden, Germany since 2005. He was born in Timisoara, Romania and emigrated to  Germany in July 1983. From 1986 to 1993, he studied  Physics at RWTH Aachen University, Germany. From 1992 to 1993, he was a Research Assistant at Physics Institute (1A) of RWTH  Aachen University. From 1994 to 2002, he was a Research Assistant at the Institute of Semi-conductor Technology of  RWTH Aachen University. In 2001, he received his PhD from RWTH Aachen University on the Topic "Particle Emission from Semi-conductor Surfaces Induced by Ion Beams and Ultra-short Laser Pulse: Applications in Nanotechnology and Analytics". In March 2003, he was a Research Assistant at the Institute of Ion Beam Physics and  Materials Research, Forschungszentrum Dresden-Rossendorf, Germany. He presented the Wilhelm und Else Heraeus-Seminar, “Ions at Surfaces: Patterns and Processes“ (scheduled June 19-23, 2005) in Bad Honnef, and he was Co-organizer of the 16th International Conference on Ion Beam Modification of Materials Organizer of the International Workshop “Nanoscale Modification of Surfaces and Thin Films” (scheduled August 30 – September 3, 2009) in Rathen.

Hosted by:  Prof. J.P. Allain, School of Nuclear Engineering and School of Materials Engineering