Pattern formation and surface analytics
Pattern formation by self-assembly occurs in various systems – geological, biological, physical – and thus on various length scales. We study self-organization which is induced by ion irradiation of surfaces and results in nanoscale pattern formation on these surfaces.
Numerous nanoscale mechanisms of erosion and diffusive as well as ballistic mass redistribution occur simultaneously on a surface subject to ion irradiation. Each of these mechanisms in itself can act on the surface in a smoothing or in a destabilizing manner, depending on external parameters. The formation of nanoscale structures of different shape and regular arrangement can result from the interplay of these mechanisms. Via readily accessible external parameter such as surface temperature, ion mass and energy, or ion incidence angle we can determine which mechanisms act dominantly and thereby steer the pattern formation process.
We work both on fundamental questions in ion-induced pattern formation and on potential applications of the resulting nanostructured surfaces:
Ion-induced pattern formation is a multifactorial process and there are different approaches to its theoretical description. By means of systematic experimental studies and numerical simulations we strive to contribute to deepen the understanding of this complex self-assembly process. Open questions concern for instance the material-dependent differences in pattern symmetry, the existence of varying structure morphologies depending on the irradiation parameters, the dynamics of pattern formation, the shape and development of patterning defects, or the pattern formation in materials of complex composition or crystal structure.
By means of physical vapour deposition we can prepare nanostructured materials such as arrays of nanowires on ion-patterned surfaces in a bottom-up fashion. We study their shape-induced magnetic, optical, electric, or thermoelectric properties.
Ion-induced pattern formation: experiment and simulation
We prepare ion-induced nanostructure patterns via large-area irradiation with low-energy noble gas ions. Our setup offers ion energies ranging from 250 to 1200 eV with ion fluxes up to 5x1015cm-2s-1, polar ion incidence angles from 0 to 90°, and sample heating up to 600 °C for samples of up to 10 mm x 10 mm. It also contains three evaporators for in-situ deposition of metal thin films.
We use a continuum equation approach to theoretically describe the pattern morphologies resulting from ion irradiation and to simulate their development via numerical integration. Out MATLAB code for such simulations is available from us on request.
AFM – for quick and facile imaging of nanostructured topographies at ambient conditions
SEM – especially suited for imaging topographies with extreme height differences or overhangs
XPS – for determining the average chemical composition of surfaces on areas of some square millimetres, as element-selective erosion during irradiation can change the surface composition
AES – employs the SEM electron beam for excitation and can therefore be used for determining the surface composition with high lateral resolution of up to 5 nm
CL – enables determination of local optical properties and thereby allows for conclusions on the density of lattice defects in crystalline material, e.g. after ion irradiation or implantation
We operate a Bruker Multimode8 instrument for AFM.
SEM, XPS, AES, CL are combined in the NanoSAM Lab S instrument, allowing for correlative surface analytics with these methods.
Moreover, we use GISAXS and XPCS as users of the NSLS-II for in-situ experiments on the dynamics of ion-induced patterning.
Offer for external researchers
We continuously offer projects for B.Sc., M.Sc., and PhD theses (the latter subject to funding availability) on the research topics described above for students of scientific or technical disciplines. Please get in touch with us!
Theory of ion-induced pattern formation:
Data-driven continuum models of surface dynamics:
Dynamics of ion-induced pattern formation, in-situ GISAXS and XPCS:
- Karl Ludwig, Boston University
- Peco Myint, Argonne National Laboratory
Ion-induced pattern formation on quasicrystalline surfaces:
- Pavol Noga, Slovak University of Technology in Bratislava
Ion-induced pattern formation on PbSnTe:
- Egor Gorlatchev, Yaroslavl Branch of the Institute of Physics and Technology of Russian Academy of Sciences
Physical vapour deposition on surfaces patterned by ion irradiation:
- Kai Schlage, Deutsches Elektronen-Synchrotron
Shape-induced magnetic properties:
- Florin Radu, Helmholtz-Zentrum Berlin
- Oleg Tretiakov, University of New South Wales
- Oleksii Volkov, HZDR
- T. Seidel: Charakterisierung von thermoelektrischen Nanostrukturen auf Substraten mit ioneninduzierter Vorstrukturierung. Diplomarbeit TU Dresden (2021)
- P. Myint, D. Erb, X. Zhang, L. Wiegart, Y. Zhang, A. Fluerasu, R.L. Headrick, S. Facsko, K.F. Ludwig: Measurement of Ehrlich-Schwoebel barrier contribution to the self-organized formation of ordered surface patterns on Ge(001). Phys. Rev. B 102 (2020) 201404(R)
- D. Erb, R. de Schultz, A. Ilinov, K. Nordlund, R. M. Bradley, S. Facsko: Nanopatterning of the (001) surface of crystalline Ge by ion irradiation at off-normal incidence: Experiment and simulation. Phys. Rev. B 102 (2020) 165422
- R. de Schultz: Ion-Induced Surface nanostructures of Germanium(001), Masterarbeit TU Dresden (2018)
- G. Malsch: Untersuchung der topologischen Defekte in Oberflächenstrukturen auf GaAs und InAs unter niedrig-energetischem Ionenbeschuss, Masterarbeit TU Dresden (2017)
- D. Gkougkou, Polarization- and Wavelength-Dependent Surface-Enhanced Raman Spectroscopy Using Optically Anisotropic Rippled Substrates for Sensing, ACS Sensors 1 (2016) 318-323
- D. K. Ball, K. Lenz, M. Fritzsche, G. Varvaro, S. Günther, P. Krone, D. Makarov, A. Mücklich, S. Facsko, J. Fassbender, M. Albrecht, Magnetic properties of granular CoCrPt:SiO2 thin films deposited on GaSb nanocones, Nanotechnology 25 (2014) 085703
- X. Ou, K.-H. Heinig, R. Hübner, J. Grenzer, X. Wang, M. Helm, J. Fassbender, S. Facsko, Nanoscale 7 (2015) 18928
- X. Ou, A. Keller, M. Helm, J. Fassbender, S. Facsko, Reverse Epitaxy of Ge: Ordered and Faceted Surface Patterns, Phys. Rev. Lett. 111 (2013) 016101
- A. Keller, S. Facsko, R. Cuerno, Numerical Integrator for Continuum Equations of Surface Growth and Erosion, in: Computational Nanotechnology, edited by S. M. Musa (CRC Press, 2013), pp. 1–27
- A. Keller and S. Facsko, Ion-Induced Nanoscale Ripple Patterns on Si Surfaces: Theory and Experiment, Materials 3 (2010) 4811 – 4841
- S. Facsko, T. Dekorsy, C. Koerdt, C. Trappe, H. Kurz, A. Vogt, H. L. Hartnagel, Formation of Ordered Nanoscale Semiconductor Dots by Ion Sputtering, Science 285 (1999) 1551 - 1553