Publikationen

Room temperature ionic liquids (RTIL) are an emerging class of electrolytes enabling high cell voltages and, in return, high energy density of advanced supercapacitors. Yet, the low temperature behavior, including freezing and thawing, is little understood when confined in the narrow space of nanopores. This study shows that RTILs may show a tremendously different thermal behavior when comparing bulk with nanoconfined properties as a result of the increased surface energy of carbon pore walls. In particular, continuous increase in viscosity is accompanied with slowed-down charge/discharge kinetics during in-situ electrochemical characterization. Freezing reversibly collapses the energy storage ability – while thawing fully restores the initial energy density of the material. For the first time, a different thermal behavior in positively and negatively polarized electrodes is demonstrated. This leads to different freezing and melting points in the two electrodes. Compared to bulk, RTIL in the confinement of electrically charged nanopores, shows the unique behavior of being highly affine for supercooling; that is, the electrode freezing during heating.

The goal of our study is to better understand the design parameters of bioinspired dry adhesives inspired by geckos. For this, we fabricated single macroscopic pillars of 400µm diameter with different aspect ratios and different tip shapes, i.e. flat tips, spherical tips with different radii, and mushroom tips with different diameters. Tilt angle dependent adhesion measurements showed that although the tip shape of the pillars strongly influences the pull-off force, the pull-off strength is similar for flat and mushroom shaped tips. We found no tilt angle dependency of adhesion for spherical tip structures, and, except for high tilt angle and low preload experiments, no tilt angle effect for mushroom tip pillars. For flat tip pillars we found a strong influence of tilt angle on adhesion, which decreased linearly with increasing aspect ratio. The experiments show that for the tested aspect ratios between 1 and 5, a linear decrease of tilt angle dependency is found. The results of our studies will help to design bioinspired adhesives for application on smooth and rough surfaces.

Abstract Correlative fluorescence microscopy combined with scanning transmission electron microscopy (STEM) of cells fully immersed in liquid is a new methodology with many application areas. Proteins, in live cells immobilized on microchips, are labeled with fluorescent quantum dot nanoparticles. In this protocol, the epidermal growth factor receptor (EGFR) is labeled. The cells are fixed after a selected labeling time, for example, 5 min as needed to form EGFR dimers. The microchip with cells is then imaged with fluorescence microscopy. Thereafter, STEM can be accomplished in two ways. The microchip with the labeled cells and one microchip with a spacer are assembled into a special microfluidic device and imaged with dedicated high-voltage STEM. Alternatively, thin edges of cells can be studied with environmental scanning electron microscopy with a STEM detector, by placing a microchip with cells in a cooled wet environment.

We investigated the friction and wear behavior as well as the mechanical properties of the periostracum of Mytilus sp. Tribological properties were determined with a reciprocal sliding microtribometer, while mechanical characterization was performed using a nanoindenter. Measurements were performed in dry and wet conditions. On the dry periostracum we found a low friction coefficient of 0.078 ± 0.007 on the young parts and a higher one of 0.63 ± 0.02 on the old parts of the shell. Under wet, saline, conditions we only observed one average coefficient of friction of 0.37 ± 0.01. Microscopic ex situ analysis indicated that dry periostracum wore rather rapidly by plowing and fatigue, while it exhibited a high wear resistance when immersed in salt water. The Young’s modulus and hardness of the periostracum were also investigated in both dry and wet conditions. Under dry conditions the Young’s modulus of the periostracum was 8 ± 3 GPa, while under wet conditions it was 0.21 ± 0.05 GPa. The hardness of dry periostracum samples was 353 ± 127 MPa, whereas the hardness of wet samples was 5 ± 2 MPa. It was found that, in the wet state, viscous behavior plays a significant role in the mechanical response of the periostracum. Our results strongly indicate that the periostracum can provide an important contribution to the overall wear resistance of Mytilus sp. shell.

The microstructural mechanisms which dictate the two-way shape-memory effect in indentation-induced NiTi surfaces is currently unknown. We create surfaces capable of thermally induced switchable topography, and characterize their behavior via white-light interferometry, X-ray and electron back scatter diffraction, and transmission electron microscopy. Results show that the switchable topography is heavily influenced by the initial microstructure, and may be inherently controlled by thermally stabilized martensite directly beneath the residual indent.

Fluorescently labeled nanoparticles are widely used to investigate nanoparticle cell interactions by fluorescence microscopy. Owing to limited lateral and axial resolution, nanostructures (<100 nm) cannot be resolved by conventional light microscopy techniques. Especially after uptake into cells, a common fate of the fluorescence label and the particle core cannot be taken for granted. In this study, a correlative approach is presented to image fluorescently labeled gold nanoparticles inside whole cells by correlative light and electron microscopy (CLEM). This approach allows for detection of the fluorescently labeled particle shell as well as for the gold core in one sample. In this setup, A549 cells are exposed to 8 nm Atto 647N-labeled gold nanoparticles (3.3 × 109 particles mL−1, 0.02 μg Au mL−1) for 5 h and are subsequently imaged by confocal laser scanning microscopy (CLSM) and transmission electron microscopy (TEM). Eight fluorescence signals located at different intracellular positions are further analyzed by TEM. Five of the eight fluorescence spots are correlated with isolated or agglomerated gold nanoparticles. Three fluorescence signals could not be related to the presence of gold, indicating a loss of the particle shell.

Transparent conducting aluminum doped zinc oxide Al:ZnO (AZO) layers have been deposited by spin coating on glass substrates using two different sols, 1-propanolic solution of Zinc and Aluminum salts (conventional sol) and a suspension of already crystalline AZO nanoparticles redispersed in 1-propanol. The coatings have been sintered in air at 600 °C for 15 min. and then post annealed in a reducing atmosphere at 400 °C for 90 min. The influence of the aluminum content in the coating sol (sol-gel layer) and in the redispersed nanoparticles (nanoparticulare suspension layer) on the optical properties and electrical resistivity have been investigated. A single step spin coated thin layer is obtained, so that multilayers coating have been used to lower the obtained sheet resistance. The visible transmission of both types of layers is high (T > 80%). The influence of the sintering temperature and the optimum doping concentration are investigated. Seven layers synthesized with Al/Zn = 1 mol.% and submitted to reducing treatment in forming gas (N2:H2 = 92:8) exhibited a sheet resistance R = 0.42 k (ρ = 7.9 × 10–3 Ω · cm) with an average transmittance of 80% at 550 nm for layer deposited from conventional sol and 36 k (ρ = 2.5 × 10–1 Ω · cm) for nanoparticles suspension layer.

In this paper, the synthesis route and growth mechanism of ZnO nanowhiskers and multipods are investigated. A simple chemical deposition route is used to synthesize tin doped zinc oxide (TZO) nanostructures using a horizontal quartz furnace. To study the effect of tin doping on the morphology of ZnO thin film, nanostructures with different morphologies and sizes were grown on silicon wafers and ITO substrates using thermal evaporation of a mixture of zinc, tin, and graphite powders at 1000 °C in a pure oxygen atmosphere. Structural studies of the synthesized ZnO nanostructures were done by means of XRD, SEM, and HRTEM. An XRD graph confirmed the formation of a pure ZnO phase. The SEM and HRTEM images exhibited nanowhiskers with dimensions of an average width of 100 nm and a few micrometers in length. The photoluminescent properties of these structures were also investigated where it shows strong blue-green emission at room temperature for the samples doped with tin.

Stable crystalline aluminum doped zinc oxide (AZO) nanopowders were synthesized using hydrothermal treatment processing. Three different aluminum precursors have been used. The Al-precursors were found to affect the morphology of the obtained nanopowders. AZO nanoparticles based on zinc acetate and aluminum nitrate have been prepared with different Al/Zn molar ratios. XRD investigations revealed that all the obtained powders have single phase zincite structure with purity of about 99%. The effect of aluminum doping ratio in AZO nanoparticles (based on Al-nitrate precursor) on structure, phase composition, and particle size has been investigated. The incorporation of Al in ZnO was confirmed by UV-Vis spectroscopy revealing a blue shift due to Burstein-Moss effect.

Dicotyledonous plants growing under limited iron availability initiate a response resulting in the solubilization, reduction, and uptake of soil iron. The protein factors responsible for these steps are transmembrane proteins, suggesting that the intracellular trafficking machinery may be involved in iron acquisition. In search for components involved in the regulation of Arabidopsis thaliana iron deficiency responses, we identified the members of the SORTING NEXIN (SNX) protein family. SNX loss-of-function plants display enhanced susceptibility to iron deficiency in comparison to the wild type. The absence of SNX led to reduced iron import efficiency into the root. SNX1 showed partial colocalization with the principal root iron importer IRON-REGULATED TRANSPORTER1 (IRT1). In SNX loss-of-function plants, IRT1 protein levels were decreased compared with the wild type due to enhanced IRT1 degradation. This resulted in diminished amounts of the IRT1 protein at the plasma membrane. snx mutants exhibited enhanced iron deficiency responses compared with the wild type, presumably due to the lower iron uptake through IRT1. Our results reveal a role of SNX1 for the correct trafficking of IRT1 and, thus, for modulating the activity of the iron uptake machinery.