Markus Geuss

Nanoscaled Discotic Liquid Crystal/Polymer Systems: Confinement Effects on Morphology and Thermodynamics

We have studied the influence of geometric confinement imposed on the supramolecular architecture of a discotic model compound confined to self-ordered nanoporous alumina. We systematically varied the pore diameter and the chemical nature of the pore walls and studied the systems thus obtained by means of wide angle X-ray diffraction and differential scanning calorimetry. A dominant planar core phase was found for high-energy pore walls consisting of alumina, whereas no apparent texture was present in the case of pore walls coated with non-polar poly(p-xylylene). Inside pores of 35 and 180 nm in diameter, pronounced geometric confinement effects and interfacial effects influence the structure formation. Additionally, we performed molecular dynamics simulations using a coarse-grained discotic potential.

Photonic Crystal Devices with Multiple Dyes by Consecutive Local Infiltration of Single Pores

[ ∗] P. W Nolte , . Dr. D. Pergande , Dr. S. L. Schweizer , Prof. R. B. Wehrspohn Martin-Luther-Univesity Halle-Wittenberg Heinrich Damerow Str. 4, 06120 Halle (Germany) E-mail: peter.nolte@physik.uni-halle.de M. Geuss , B. Makowski , Prof. C. Weder Adolphe Merkle Institute and Fribourg Center for NanomaterialsUniversity of Fribourg P.O. Box 209, CH-1723 Marly (Switzerland) B. Makowski , Prof. C. Weder Case Western Reserve University Department of Macromolecular Science and Engineering 2100 Adelbert Rd., Cleveland, OH 44107–7202 (USA) R. Salzer , Prof. R. B. Wehrspohn Fraunhofer Institute for Mechanics of Materials Walter-Hulse-Strase 1, 06120 Halle (Germany) P. Mack Institut fur Nanotechnologie Karlsruhe Institute of Technology (KIT) Hermann-von-Helmholtz-Platz 176344 Eggenstein-Leopoldshafen (Germany) Dr. D. Hermann , Prof. K. Busch Institut fur Theoretische Festkorperphysik and DFG-Center for Functional Nanostructures (CFN) Karlsruhe Institute of Technology (KIT) Wolfgang-Gaede-Strasse 1, 76131 Karlsruhe (Germany) M. Geuss , Prof. M. Steinhart Max Planck Institute of Microstructure Physics Weinberg 2, 06114 Halle (Germany) Prof. M. Steinhart Institute for ChemistryUniversity of Osnabruck 49069 Osnabruck (Germany)

Formation of straight 10 nm diameter silicon nanopores in gold decorated silicon.

We observe pore formation with diameters in the 10 nm range in silicon when it is covered with gold particles. This pore etching occurs when the sample is put in 5 wt % hydrofluoric acid (HF) solution for a few minutes. The pores form along the 100 direction, which is also the preferred direction of macro- and mesopores electrochemically etched into silicon. No etching occurs if the dissolved oxygen is removed from the aqueous HF solution or the gold is removed from the silicon surface. This leads to the assumption that the dissolved oxygen acts as an oxidant as in the case of stain etching with gold as cathodic material. A tentative model is suggested to explain why all of the observed nanopores have roughly the same diameter of about 10 nm. These pores can occur for inhomogeneously gold-covered planar silicon surfaces but also in MBE (molecular beam epitaxy) grown silicon nanowires since these nanowires are covered unintentionally with gold nanoclusters at their cylindrical surface.

Manipulating Semicrystalline Polymers in Confinement

Because final properties of nanoscale polymeric structures are largely determined by the solid-state microstructure of the confined polymer, it is imperative not only to understand how the microstructure of polymers develops under nanoscale confinement but also to establish means to manipulate it. Here we present a series of processing strategies, adapted from methods used in bulk polymer processing, that allow us to control the solidification of polymer nanostructures. First, we show that supramolecular nucleating agents can be readily used to modify the crystallization kinetics of confined poly(vinylidene fluoride) (PVDF). In addition, we demonstrate that microstructural features that are not traditionally affected by nucleating agents, such as the orientation of crystals, can be tuned with the crystallization temperature applied. Interestingly, we also show that high crystallization temperatures and long annealing periods induce the formation of the γ modification of PVDF, hence enabling the simple production of ferro/piezoelectric nanostructures. We anticipate that the approaches presented here can open up a plethora of new possibilities for the processing of polymer-based nanostructures with tailored properties and functionalities.

Infiltration of individual pores in macroporous silicon photonic crystals

A new and promising approach for the design and fabrication of novel optical devices is the functionalization of individual pores in 2D photonic crystals (PhC). This can be done by infiltrating the pores with polymers or dyes. We present a method to locally infiltrate individual pores. This new technique enables the fabrication of a new class of devices, such as optical switches or multiplexers. For the infiltration of individual pores 2D PhC templates made of macroporous silicon were used. Local addressing of the pores is carried out by using focused ion beam technology. For the infiltration itself the wetting assisted templating process is applied. We will present experimentally the infiltration of different polymers and different optical designs.

Anisotropic domain orientation and local, reversible polarisation switching in textured ferroelectric polymer nanofibers

We showed oriented crystallization of ferroelectric nanofibers of P(VDF-TrFE) in nanoporous templates after melt wetting. 2D-PFM imaging and local poling of homogenously polarized domains with orientations inclined to the nanofiber long axis demonstrates how the oriented crystal growth restricts the possible orientation directions which can be address by local domain switching.