Enrico Langer

An extreme biomimetic approach: hydrothermal synthesis of β-chitin/ZnO nanostructured composites

β-Chitinous scaffolds isolated from the skeleton of marine cephalopod Sepia officinalis were used as a template for the in vitro formation of ZnO under conditions (70 °C) which are extreme for biological materials. Novel β-chitin/ZnO film-like composites were prepared for the first time by hydrothermal synthesis, and were thoroughly characterized using numerous analytical methods including Raman spectroscopy, HR-TEM and XRD. We demonstrate the growth of hexagonal ZnO nanocrystals on the β-chitin substrate. Our chitin/ZnO composites presented in this work show antibacterial properties against Gram positive bacteria and can be employed for development of inorganic-organic wound dressing materials.

Extreme biomimetic approach for developing novel chitin-GeO2 nanocomposites with photoluminescent properties

This work presents an extreme biomimetics route for the creation of nanostructured biocomposites utilizing a chitinous template of poriferan origin. The specific thermal stability of the nanostructured chitinous template allowed for the formation under hydrothermal conditions of a novel germanium oxide-chitin composite with a defined nanoscale structure. Using a variety of analytical techniques (FTIR, Raman, energy dispersive X-ray (EDX), near-edge X-ray absorption fine structure (NEXAFS), and photoluminescence (PL) spectroscopy, EDS-mapping, selected area for the electron diffraction pattern (SAEDP), and transmission electron microscopy (TEM)), we showed that this bioorganic scaffold induces the growth of GeO2 nanocrystals with a narrow (150–300 nm) size distribution and predominantly hexagonal phase, demonstrating the chitin template’s control over the crystal morphology. The formed GeO2–chitin composite showed several specific physical properties, such as a striking enhancement in photoluminescence exceeding values previously reported in GeO2-based biomaterials. These data demonstrate the potential of extreme biomimetics for developing new-generation nanostructured materials.

Synthesis of nanostructured chitin–hematite composites under extreme biomimetic conditions

Chitin of poriferan origin is a unique and thermostable biological material. It also represents an example of a renewable materials source due to the high regeneration ability of Aplysina sponges under marine ranching conditions. Chitinous scaffolds isolated from the skeleton of the marine sponge Aplysina aerophoba were used as a template for the in vitro formation of Fe2O3 under conditions (pH ∼ 1.5, 90 °C) which are extreme for biological materials. Novel chitin–Fe2O3 three dimensional composites, which have been prepared for the first time using hydrothermal synthesis, were thoroughly characterized using numerous analytical methods including Raman spectroscopy, XPS, XRD, electron diffraction and HR-TEM. We demonstrate the growth of uniform Fe2O3 nanocrystals into the nanostructured chitin substrate and propose a possible mechanism of chitin–hematite interactions. Moreover, we show that composites made of sponge chitin–Fe2O3 hybrid materials with active carbon can be successfully used as electrode materials for electrochemical capacitors.

Lattice constant determination from Kossel patterns observed by CCD camera

The Kossel technique is known due to its precision for lattice constant determination in micro ranges by use of X-ray films. Recently we observed the Kossel interferences also by a CCD camera in a good quality. Thus, the diffraction interferences could be immediately processed and evaluated by computer permitting considerable time saving. In order to obtain the similar accuracy as for measurements with X-ray films further technical and experimental improvements were necessary, especially for a better contrast to observe intersection points of several weak reflections, for evaluating digital patterns, for optimizing of the shortest focus-screen distance and for considering the image field curvature of the objective. As a result, a precision in lattice constant determination could be achieved at a Fe-crystal coming relatively close to the one of comparable X-ray film patterns, which is still about one order of magnitude better for the time being.

KOPSKO: a Computer Program for Generation of Kossel and Pseudo Kossel Diffraction Patterns

Diffraction techniques are widely used especially as additional tools for analytical microprobe analysis. A supplementary device to a scanning electron microscope (SEM) allows taking of X-ray lattice source and wide angle interference patterns, now termed Kossel and Pseudo Kossel patterns, respectively, in transmission and back reflection arrangement as reported by DABRITZ et al. (1986, 1997a,b). The developed program KOPSKO simulates exactly the entire reflection system of Kossel and Pseudo Kossel diffraction patterns basing on the geometric diffraction theory. It permits phase, orientation, and structure determination. The present paper shows the wide range of possibilities using the computerized analysis in this field. Initially it deals with simulation of Kossel patterns, which are excellent suitable for a precise determination of lattice constants in the micro range for instance. A new way for simulation of Pseudo Kossel diffraction patterns using three dimensional vector algebra to calculate reflections in point by point procedure is presented in the second part. The attained precise coincidence of simulation and experimentally taken Pseudo Kossel patterns allows a relatively easy determination of crystallographic data of mono- and polycrystals. Particularly the program is designed to determine lattice constants precisely, for the complex divergent beam X-ray interferences, too. Through the three dimensional simulation it takes into account shade originated by the target holder. Moreover, the three dimensional point by point procedure enables the localization of lattice imperfections as well as the consideration of grain size effects in polycrystals. which lead to interruptions of Pseudo Kossel lines. By simulation of diffraction patterns of polycrystalline materials the study of such specimens is essentially simplified.

New observation method for divergent beam X-ray diffraction patterns

The simultaneous observation of X-ray reflections by a high-quality charge coupled device (CCD) camera in a scanning electron microscope is presented. The possibility of immediate further processing and evaluation of the images by computer, avoiding the extensive photographic X-ray film procedure, is discussed. The divergent beam X-ray method has considerable importance for investigations in materials research. The experimental set-up is described and the advantageous application of the camera is demonstrated for different examples.

Extreme biomimetics: A carbonized 3D spongin scaffold as a novel support for nanostructured manganese oxide(IV) and its electrochemical applications

Composites containing biological materials with nanostructured architecture have become of great interest in modern materials science, yielding both interesting chemical properties and inspiration for biomimetic research. Herein, we describe the preparation of a novel 3D nanostructured MnO2-based composite developed using a carbonized proteinaceous spongin template by an extreme biomimetics approach. The thermal stability of the spongin-based scaffold facilitated the formation of both carbonized material (at 650 °C with exclusion of oxygen) and manganese oxide with a defined nanoscale structure under 150 °C. Remarkably, the unique network of spongin fibers was maintained after pyrolysis and hydrothermal processing, yielding a novel porous support. The MnO2-spongin composite shows a bimodal pore distribution, with macropores originating from the spongin network and mesopores from the nanostructured oxidic coating. Interestingly, the composites also showed improved electrochemical properties compared to those of MnO2. Voltammetry cycling demonstrated the good stability of the material over more than 3,000 charging/discharging cycles. Additionally, electrochemical impedance spectroscopy revealed lower charge transfer resistance in the prepared materials. We demonstrate the potential of extreme biomimetics for developing a new generation of nanostructured materials with 3D centimeter-scale architecture for the storage and conversion of energy generated from renewable natural sources.

Chemically controlled micro-pores and nano-filters for separation tasks in 2D and 3D microfluidic systems

Molecule filtering or particle separation is a complex task in microfluidics. Passive structures or polymer based systems like hydrogels are normally used elements. PNIPAAm (poly-N-isopropylacrylamide) hydrogels are known for their capability to work as nano-filters to separate small molecules from their environment and protect them from degrading enzymes by the polymer network. PNIPAAm based active micro-pores were also demonstrated for particle separation. Normally, changes in temperature are used to alter the permeation properties of such hydrogel elements. To handle limiting factors such as separate temperature control for each element, chemical signals can be used to alter the permeation. Here, we present a new way to adapt the size exclusion functionality of PNIPAAm-based nano-filters or micro-pores. PNIPAAm hydrogels respond to organic solvent concentrations by shrinking or swelling. We use this responsiveness to alter the hydrogel mesh size or to adjust the size of a micro-pore. We show the filter functionality for two model molecules: the enzyme horse radish peroxidase and the fluorescence molecule fluorescein. Furthermore, the adjustment of the size of a micro-pore in a continuous way is demonstrated, so that pore sizes between the closed and open state can be addressed and kept permanently.

Ion Beam Preparation Procedures for Three-dimensional SEM Resolved Kikuchi (EBSD) and Kossel Microdiffraction Analysis of Deformed Metals

The SEM provides information not only on the sample surface and near-surface regions concerning topography, composition, crystal orientation etc. With special preparation techniques the full 3D microstructure can be detected. The deformation-free revealing of the internal structure is not possible with mechanical cutting and grinding. Chemical and electrolytic methods allow only selected material-specific solutions. Ion beam preparation has essential advantages compared with conventional techniques. Especially for mechanically deformed metal samples with small dimensions special ion beam processing steps are required. The well established FIB technology is only useful for very small selected regions with micrometer dimensions. Here the problem will be solved to cut and to investigate samples with cross sections of typically 20 μm x 400 μm and 4 mm length after well defined deformation by microscopy and microdiffraction in the SEM over the full sample volume. The sample shape and size are shown in Fig. 1. After defined tensile tests these samples have been cut longitudinally (cut 1) and transverse (cut 2) by ion beam slope cutting and the macroarea was etched chemically (region 3). The ion beam cutting method [1] was carried out with the Gatan Precision Etching Coating System (PECS) acc. to Fig. 2. The broad ion beam is directed onto the sample mounted under a blind with a sharp edge. The ion gun allows to produce a beam of inert gas or reactive ions with energies up to 10 keV and densities up to 40 μA/mm. The processes can be observed by optical microscopy. A new stage allows sample positioning, tilting and rotation, blind mounting and adjustment with accurate sample transfer into the SEM for the final inspection. Fig. 3 shows a detail of the longitudinal ion beam cut area. In Fig. 4 the ion beam cut area of the full cross section (transversal cut) is shown. The cutting steps were carried out with 7 keV Krypton ions. The texture analysis by EBSD is shown in Fig. 5 for the cuts corresponding to Fig. 1 by Orientation Imaging Microscopy (OIM) maps of a 20 μm thin rolled Cu foil after a tensile test. More detailed discussion of the texture modified by deformation will be given in [2]. Also X-ray Kossel microdiffraction pattern have been detected of a tensile deformed Ni crystal [3]. The Kossel pattern in Fig. 6 shows an example of strong broadening and anisotropic intensity change of reflections due to the deformation process. EBSD provides information on crystallographic orientations, whereas X-ray Kossel microdiffraction pattern allow profound statements of the real microstructure. For both techniques the ion beam procedures are excellent tools to produce cut areas with high accuracy and to combine it very well with additional analysing methods.