Publikationen

Indium tin oxide (ITO) thin film is one of the most widely used as transparent conductive electrodes in all forms of flat panel display (FPD) and microelectronic devices. Suspension of already crystalline conductive ITO nanoparticles fully dispersed in alcohol was spun, after modifying with coupling agent, on glass substrates. The low cost, simple and versatile traditional photolithography process without complication of the photoresist layer was used for patterning ITO films. Using of UV light irradiation through mask and direct UV laser beam writing resulted in an accurate linear, sharp edge and very smooth patterns. Irradiated ITO film showed a high transparency (similar to 85%) in the visible region. The electrical sheet resistance decrease with increasing time of exposure to UV light and UV laser. Only 5 min UV light irradiation is enough to decrease the electrical sheet resistance down to 5 k Omega square.

The corundum structures of In2O3:Sn (ITO) nanoparticles were synthesized by hydrothermal processing of InCl3 and SnCl4·5H2O precursor at low temperature of 250 °C and 40 bar pressure for 3 h. The precursor was precipitated in a white gel of InOOH. After drying at 150 °C in air, it was crystallized in orthorhombic structure. InOOH powder was transformed into dark-gray rhombohedral In2O3 by sintering at 420 °C in forming gas for 1 h. The samples were characterized by means of XRD, SEM, and TEM. The particle size of the resulted ITO powder was about 32 nm.

Low temperature processable materials with high dielectric constants are required for application on flexible organic substrates, for example, in printed electronics. To date, mainly organic polymers with embedded functional particles have been investigated for this purpose. For the first time, we present a printable dielectric composite material composed of ferroelectric high permittivity particles (BaTiO3) bonded by a mainly inorganic sol-gel derived network. The exemplary optimization of the properties by varying the sol-gel precursor illustrates the potential of sol-gel chemistry for printable functional materials. An operational gravure printed capacitor including printed silver electrodes is presented. The measured dielectric constants are among the highest reported in literature for low temperature cured films with moderate dissipation factors. Besides these promising dielectric properties, this composite film shows a ferroelectric response.

Proton-conducting gel polymer electrolytes based on gelatin plasticized with glycerol and containing acetic acid were investigated, characterized, and applied to electrochromic window. For glycerol contents varying from 7% to 48%, the conductivity of the uniform and predominantly amorphous gel electrolyte was found to follow a Vogel-Tamman-Fulcher behavior with the temperature. Typically, for the electrolyte chosen to make 7×2 cm2 electrochromic smart window with the configuration: glass/fluor-doped tin oxide (FTO)/WO3/gelatin electrolyte/CeO2-TiO2/FTO/glass and containing 28% of glycerol, the conductivities were found to be of the order of 5×10−5 S/cm at room temperature and 3.6×10−4 S/cm at 80°C. The device was characterized by spectroelectrochemical techniques and was tested up to 10,000 cycles showing a fast coloring/bleaching behavior, where the coloring process was achieved in 10 s and the bleaching in 2 s. The transmission variation at the wavelength of 550 nm was about 15%. The cyclic voltammograms showed a very good reversibility of the cathodic/anodic processes, and the charge density was about 3.5 mC/cm2. The memory tests showed that the transmittance in the colored state increased by 8% in 90 min after removing the potential.

The feathers in the train of the peacock serve not for flying but for sexual display. They are long, slender beams loaded in bending by their own weight. An outer circular conical shell, the cortex, is filled by a closed foam of 7.6% relative density, the medulla, both of feather keratin. Outer diameter and thickness of the cortex decrease linearly from the body toward the tip. This self-similar geometry leads to a division of labor. The cortex (longitudinal Young's modulus 3.3 GPa, transverse modulus 1 GPa) provides 96% of the longitudinal strength and bending rigidity of the feather. The medulla (Young's modulus 10 MPa) provides 96% of the transverse compressive rigidity. Fracture stress of the cortex, both longitudinal and transverse, is 120 MPa.

The twelve membered and eighteen membered cyclosiloxazanes [Me2SiOSiMe2N(H)SiMe2O]2 (3) and [Me2SiOSiMe2N(H)SiMe2O]3 (4) have been obtained as colourless liquids from the reaction of 1,5-Dichlorohexamethyltrisiloxane with ammonia at-50 °C without any solvent. For compound 3 and 4, the yield is 30 % and 43 %, respectively. The treatment of 3 with two equivalents of n-butyllithium in n-hexane leads in almost quantitative yield (93 %) to the dilithiumsilylamide [Me2SiOSiMe2N(Li)SiMe2O]2 (5). Compound 5 can be isolated at room temperature and recrystallized from benzene without any decomposition or contraction of the ring size. An X-ray structure determination on [Me2SiOSiMe2N(Li)SiMe2O]2 (5) reveals a waved crown-like twelve membered Si6N2O4-cycle. Each of the two lithium ions is coordinated by two nitrogen and two oxygen atoms leading to a square pyramid, in which the metal occupies the apex. The two square-pyramidal coordination figures are located above and below the waved crown-like Si6N2O4-ring sharing a common edge by the atoms N(1) and N(2). All synthesised compounds have been characterised by spectroscopic methods. Because of the lower solubility of the dilithiumsilylamide 5, only a 1H-NMR could be applied for further characterisation in solution.

Nature has developed reversibly adhesive surfaces whose stickiness has attracted much research attention over the last decade. The central lesson from nature is that "patterned" or "fibrillar" surfaces can produce higher adhesion forces to flat and rough substrates than smooth surfaces. This paper critically examines the principles behind fibrillar adhesion from a contact mechanics perspective, where much progress has been made in recent years. The benefits derived from "contact splitting" into fibrils are separated into extrinsic/intrinsic contributions from fibril deformation, adaptability to rough surfaces, size effects due to surface-to-volume ratio, uniformity of stress distribution, and defectcontrolled adhesion. Another section covers essential considerations for reliable and reproducible adhesion testing, where better standardization is still required. It is argued that, in view of the large number of parameters, a thorough understanding of adhesion effects is required to enable the fabrication of reliable adhesive surfaces based on biological examples.

ZO-1 is a peripheral protein that plays a central role in the macromolecular assembly of tight junctions by interacting with integral proteins (occludin, claudins, JAMs) of the membrane of adjoining cells, with the actin cytoskeleton, and with nuclear factors. Human ZO-1 is expressed in all epithelia and some specialized endothelia as variable amounts of two related isoforms, which originate from the alternatively spliced mRNA transcripts α+ and α- and whose specific differential role is still unknown. Moreover, little is known about the timing of expression of ZO-1 isoforms at the protein and mRNA level. This study shows that during growth of freshly plated Caco-2 cells the α+/α- ratio increased as a result of simultaneous increase of α+ and decrease of α-. Differences in the isoform ratio also correlated with differences in epithelium differentiation. This was determined by aminopeptidase-N measurements of cells grown on conventional substrates and on modified, micro/nano-patterned surfaces. A comparable shift of ZO-1 isoforms was not observed in other tumour cell lines of non-intestinal origin (A549, Calu-3). Pancreatic stem cells propagated without exogenous differentiation stimuli display a slight, stable prevalence of the α- isoform. Of the intestinal cell lines examined (Caco-2 and T84) only Caco-2 cells displayed a dramatic shift in isoform expression. This suggests that this tumour cell line retains to a higher degree a developmental program related with the dynamic of enterocytic differentiation in vivo.

Gecko inspired adhesives are surfaces with many microscale pillars that form Van der Waals forces with other surfaces. They differ from conventional tape in that adhesion is reversible and has the potential for switchability. These properties make gecko adhesives interesting for various biomedical applications. The two objectives of this project were to investigate the formation of biofilms on such surfaces and how the surfaces affect cell development. The developmental stages of the model organism Dictyostelium discoideum were observed by time lapse photography using light and environmental scanning electron microscopy. This study shows that micropatterned surfaces can be used as a biophysical tool to interfere with multicellular tissue formation in multiple ways.