Electron Microscopy

Structural Analysis of H-bridged Materials Using Electron Diffraction

Physical porperties of matter are influenced by the internal structure of the material. Structural characterization of self-organizing materials in an important step for the unterstanding of H-bridging and molecular organization, which cause changes in the observed properties. Unfortunately, cristallinity of polymeric or organic systems is often too poor for single-crystal x-ray diffraction. Alternatively, powder-diffraction is done, which provides one-dimensional data, which is often modified by overlapping reflexes, contaminations, or preferred orientations. Electron-diffraction is in many cases the only possibility for the structural characterization of nanocrystalline compounds.

Data of electron diffraction experiments are collected as 2D-slices throughout the reciprocal space. Combination of the data results in a 3D data-set. Nano Electron Diffraction (NED) allows for a restriction of the electron beam to 10-50nm. Via combination with imaging in raster-mode, a soft technique is developed, especially designed for beam-sensitive materials. For small crystals with low symmetry, manual data-aquisition is often impossible. Therefore, we develop, together with the company FEI, a module for automated data aquisition [1].

After assigning cell-parameters and refining the data with the help of powder-diffraction, identification of zones is possible. The size of the 3D datasets are comparable with those from powder diffraction, but intensities are affected by dynamic diffraction and show gaps in the reciprocal space. Dynamic effects are very weak in organic materials and can be negelcted in the first analysis. This structural model can be refinde by powder-diffraction data via Rietveld methods [2]. The combination of complementary data from single-cristal electron and powder-xray diffraction turns out to be an ideal tool to determine the structure of nanocrystalline pigments, non-linear optical active organic molecules, ferroelectric monomers and polymers, and polyelectrolytes [3-5].

In this project, the above mentioned technique is used to determine the structure benylediamide-dimers with different substituents, which will serve as benzoxazine model system [6]. Furthermore, examination of oligo(p-benzamide)-b-poly(ethylene glycole) blockcopolymers and oligo-p-benzamides is done. Those systems are important supermolecular building blocks with designable aggregation strength via the oligomer-length [7,8].

[1] U. Kolb, T. Gorelik, C. Kübel, M.T. Otten, and D. Hubert, Ultramicroscopy, 107, 507-513 (2007).

[2] MaterialStudio 4.0 and Cerius 2 version 4.2 MS, Accelrys Inc., 9685 Scranton Road, San Diego, CA 92121 - 3752, USA.

[3] U.Kolb and G. Matveeva, Z. Krist., 218, (2003) 259-268.

[4] U.Kolb et al. in: Electron Crystallography, Weirich et al. (eds.), Kluwer Academic Publishers, Netherlands, NATO ASI Series E: Applied Sciences. 211, (2005) 421-433 and 411-420.

[5] U. Kolb, K. Büscher, Ch. Helm, A. Lindner, A.F. Thünemann, M. Menzell, Masayoshi Higuchi and D. G. Kurth, PNAS, 103, 10202-10206 (2006).

[6] G. Goward, D. Sebastiani, I. Schnell, H.W. Spiess, H.-D. Kim, H. Ishida, J. Am. Chem. Soc., 125 5792 (2006).

[7] H.M. König, R. Abbel, D. Schollmeyer, A.F.M. Kilbinger, Org. Lett. 8, 1819 (2006).

[8] T.W. Schleuss, R. Abbel, M. Groß, D. Schollmeyer, H. Frey, M. Maskos, R. Berger and A.F.M. Kilbinger, Angew. Chem., 118, 3036, Angew. Chem. Int. Ed., 45, 2969 (2006).

Characterization of Nanostructured Materials by Electron Microscopy

Visualizing structures of self-organizing systems, preparation of dry samples for electron microscopy can lead to artefacts like the collaps of the structure, reorganisation, or aggregation. In order to prevent this, vitrification (fast cooling from solution) is necessary. This technique was used to image the structure of smectic liquid crystaline colloids [1], lipid vesicels of various sizes and filled with agents [2], or for intelligent hydrogels marked with magnetic nanoparticles [3]. Besides the well-known vitrification from aqueous solutions, structures are also vitrified from different organic solvents. Analyzed so far are blockcopolymers like polystyrene-b-poly(2-vinyllpyrrolidone) from benzene [4], oligo (p-benzamide)-b-poly(ethylene-glycole) from chloroform [5], and PWO-b-PTMSPMA vesicles from methanole/water mixtures [4]. Furthermore, various nanomaterials are characterized using high-resolution transmission electron microscopy HRTEM, scanning electron microscopy STEM, and elemental analyses like EELS and EDX. Some examples are single-molecule nanogels [6], tetra-pod semiconductor nanoparticles [7], and surface-modified nanoparticles [8,9].

[1] M. Vennes, R. Zentel, M. Rössle, M. Stepputat, U. Kolb, Adv. Mat. 17(17), 2123 (2005).

[2] Cooperation Shazly, Institute for Pharmacy, Johannes Gutenberg University, Mainz.

[3] Cooperation Annette Schmidt, Heinrich Heine-University, Düsseldorf.

[4] Cooperation Project A2 M. Schmidt/A13 M.Maskos, Institute for Physical Chemistry, Johannes Gutenberg University, Mainz.

[5] Cooperation Project A11 A. Kilbinger H.M. König, R. Abbel, D. Schollmeyer, A.F.M. Kilbinger, Org. Lett. 8, 1819 (2006); T.W. Schleuss, R. Abbel, M. Groß, D. Schollmeyer, H. Frey, M. Maskos, R. Berger and A.F.M. Kilbinger, Angew. Chem., 118, 3036, Angew. Chem. Int. Ed., 45, 2969 (2006).

[6] Günter Wulff, Byong-Oh Chong and Ute Kolb Angew. Chem., 118, 3021-3024 Angew. Chem. Int. Ed., 45, 2955-2958 (2006).

[7] Renguo Xie, Xinhua Zhong, Ute Kolb and Thomas Basché, Small, accepted.

[8] Tahir MN, Eberhardt M, Therese HA, Kolb U, Theato P, Müller WEG, Schröder H-Ch. and Tremel W Angew. Chem. Int. Ed. 45(29) 4803-4809 (2006).

[9] Tahir MN, Theato P, Oberle P, Gennadij Melnyk, Simon Faiss, Ute Kolb, Andreas Janshoff, Michael Stepputat and Wolfgang Tremel Langmuir 22(12)5209-5212 (2006).