The principle of biodegradation has been considered for many years in the development of cardiovascular stents, especially for patients with congenital heart defects. A variety of materials have been examined with regard to their suitability for cardiovascular devices. Iron- and magnesium-based stents were investigated intensively during the last years. It has been shown, that iron, or iron based alloys have slow degradation kinetics whereas magnesium-based systems exhibit rapid degradation rates. Recently we have developed fluoride coated binary magnesium-calcium alloys with reduced degradation kinetics. These alloys exhibit good biocompatibility and no major adverse effects toward smooth muscle and endothelial cells in in vitro experiments. In this study, these alloys were investigated in a subcutaneous mouse model. Fluoride coated (fc) magnesium, as well as MgCa0.4%, MgCa0.6%, MgCa0.8%, MgCa1.0%, and a commercially available WE43 alloy were implanted in form of (fc) cylindrical plates into the subcutaneous tissue of NMRI mice. After a 3 and 6 months follow-up, the (fc) alloy plates were examined by histomorphometric techniques to assess their degradation rate in vivo. Our data indicate that all (fc) alloys showed a significant corrosion. For both time points the (fc) MgCa alloys showed a higher corrosion rate in comparison to the (fc) WE43 reference alloy. Significant adverse effects were not observed. Fluoride coating of magnesium-based alloys can be a suitable way to reduce degradation rates. However, the (fc) MgCa alloys did not exhibit decreased degradation kinetics in comparison to the (fc) WE43 alloy in a subcutaneous mouse model.

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Resistance switching in metal -insulator -metal (MIM) structures with transition metal oxides as the insulator material is a promising concept for upcoming non-volatile memories. The electronic properties of transition metal oxides can be tailored in a wide range by doping and external fields. In this study SrTiO 3 single crystals are subjected to high temperature vacuum annealing. The vacuum annealing introduces oxygen vacancies, which act as donor centers. MIM stacks are produced by physical vapor deposition of Au and Ti contacts on the front and rear face of the SrTiO 3 crystal. The time dependent forming of the MIM stacks under an external voltage is investigated for crystals with varying bulk conductivities. For continued formation, the resistivity increases up to failure of the system where no current can be measured anymore and switching becomes impossible.

Perovskite-type transition metal oxides have great potential as storage material in resistive random-access memory (RRAM) devices. Typical non-volatile memory cells are realized in metal-insulator-metal (MIM) stacks with insulator thicknesses of few nanometers. We report on the investigation of single-crystal SrTiO3 to understand the role of volume and interface real structure for the electrical conductivity in such materials. Conductivity in SrTiO3 single crystals was established by a reducing high vacuum (HV) annealing introducing charged oxygen vacancies acting as donor centers. Titanium electrodes are evaporated on both crystal faces to obtain an MIM element.

In oxides with perovskite-type of structure, oxygen can be a sufficiently mobile defect even at room temperature when an electric field of sufficient strength (~1000 V/mm) is applied. Our in-situ investigations of metal/SrTiO 3 junctions revealed reversible structural changes and the formation of nonstoichiometric regions during the application of external electric fields. This might be caused by a field-induced redistribution of oxygen vacancies. The investigations were carried out using wide-angle X-ray scattering, X-ray absorption spectroscopy, nanoindentation and time-dependent electric measurements. Motivated by the successful use of SrTiO 3 with different doping metals for memory cells on the basis of resistive switching in combination with the findings on the major importance of oxygen vacancy redistribution, we want to show the possibility of realizing a resistance change memory based on vacancy-doped SrTiO 3 . The formation of corresponding metal/SrTiO 3 junctions in an electric field will be discussed as well as the switching between ohmic and Schottky-type resistive properties. A notable hysteresis in the current-voltage characteristics can be used to carry out Write, Read and Erase operations to test the memory cell properties of such junctions. But whereas the electric field-induced formation of Schottkytype junctions may be explained by oxygen vacancy redistribution, the resistive switching is preferably discussed in terms of vacancies serving as electron trap states at the metal/oxide interface. Grazing Incidence X-ray diffraction (GIXRD) is a surface Xray diffraction method for the analysis of mineral surfaces and interfaces on atomic scale [1,2]. This method requires very flat and large single crystal surfaces with a rms-roughness well below 10 nm. Therefore crystal surfaces used in GIXRDexperiments are analyzed for surface topography and roughness. Atomic force microscopy (AFM) provides a simple, inexpensive and fast technique to investigate the macroscopic surface structure and measure the surface roughness. TiO 2 is the most widely used photocatalytic material for heterogeneous photocatalytic oxidation (PCO) processes [3]. Photocatalytic thin films consist of a mixture of rutile and anatase nanocrystals, where the anatase surfaces are the most active part in the PCO process [4]. The structure and properties of the most abundant (101) and (001) anatase crystal faces are studied with a wide range of experimental and simulation techniques, however, to the best of our knowledge, exclusively in vacuum conditions. GIXRD experiments on anatase surfaces in environmental conditions will provide information about the surface and interface structure of natural anatase crystals, allowing to analyse the surface properties in more "real" conditions compared to UHV experiments. In preparation of these GIXRD experiments here the (101) and (001) surfaces of anatase single crystals from Hardangervidda, Norway, were characterized with atomic force microscopy (AFM). Four bipyramidally shaped crystals with (101) ...