Chemical nanoroughening of Ti40Nb surfaces and its effect on human mesenchymal stromal cell response.

Samples of low modulus beta-type Ti40Nb and cp2-Ti were chemically treated with 98% H2 SO4 + 30% H2 O2 (vol. ratio 1:1) solution. Surface analytical studies conducted with HR-SEM, AFM, and XPS identified a characteristic nanoroughness of the alloy surface related with a network of nanopits of ∼25 nm diameter. This is very similar to that obtained for cp2-Ti. The treatment enhances the oxide layer growth compared to mechanically ground states and causes a strong enrichment of Nb2 O5 relative to TiO2 on the alloy surface. The in vitro analyses clearly indicated that the chemical treatment accelerates the adhesion and spreading of human mesenchymal stromal cells (hMSC), increases the metabolic activity, and the enzyme activity of tissue non-specific alkaline phosphatase (TNAP). Surface structures which were generated mimic the cytoplasmic projections of the cells on the nanoscale. Those effects are more pronounced for the Ti40Nb alloy than for cp2-Ti. The relation between alloy surface topography and chemistry and cell functions is discussed.

In situ stress evolution during and after sputter deposition of Al thin films.

The stress, growth, and morphology evolution of Al thin films up to 300 nm thick, sputter deposited at a constant rate of 0.04 nm s(-1) onto thermally oxidized Si(100) substrates have been investigated for various sputter pressures in the range from 0.05 to 6 Pa. The stress evolution has been studied during and after the film deposition by means of in situ substrate curvature measurements using an optical two-beam deflection method. In order to obtain insight into the mechanisms of stress generation and relaxation, the microstructure of the films was investigated by scanning electron microscopy, focused-ion-beam microscopy, and atomic force microscopy. The stress evolution during the early stage of deposition of films is consistent with the Volmer-Weber growth mode known for metals with high adatom mobility. For thicker films, the compressive stress increases in the sputter pressure range of 0.05-0.5 Pa, whereas at even higher sputter pressures a transition from compressive to tensile stress takes place. This transition is correlated with a change from a relatively dense to a more porous microstructure characterized by decreasing mass density and increasing electrical resistivity with increasing sputter pressure. The dependence of the stress and microstructure on the sputter pressure can be consistently understood through a combination of the stress mechanisms for vapor and sputter deposited films proposed in the literature.

Stereological analysis and modelling of gradient structures

Gradient structures are inhomogeneous along a particular gradient direction but homogeneous perpendicular to that direction. Consequently, structural parameters such as volume fraction or surface area density are local characteristics which depend on the 'vertical' coordinate with respect to the 'vertical' gradient axis. Analogously, models for gradient structures have model parameters depending on the vertical coordinate z. For example, a Voronoi tessellation with a gradient is generated by a gradient point process with a local intensity which is a function of z. Similarly, a gradient germ grain model is obtained from a gradient point process where the grain size distribution may also depend on z. For a gradient Boolean model, local volume fraction VV(z) and local surface area density SV(z) can be calculated from the model parameters. Stereological methods for gradient structures are based on vertical sections parallel to the gradient direction. Estimation of VV(z), SV(z) and local length density LV(z) is done by lineal analysis using horizontal test lines with vertical coordinate z. Similarly, lineal analysis is used to estimate local mean cell volume of gradient tessellations. For the estimation of local particle number density and size in the spirit of the Wicksell problem the use of kernel methods and distributional assumptions is required.

Characterization of ultra smooth interfaces in Mo/Si-multilayers.

The interface structure of Mo/Si-multilayers prepared by Pulsed Laser Deposition (PLD) on Si substrates at room temperature has been investigated. Already the in-situ ellipsometer data acquired during film growth indicate a particular behaviour of this material system that is caused by reaction/diffusion processes of the condensing atoms. MoSi(x) interlayers are formed both at the Mo on Si- and at the Si on Mo-interfaces. The results of multilayer characterization carried out by SNMS and RBS show similar concentration profiles for both types of the interlayers. More detailed information about interface structure and morphology can be provided by HREM investigations. In the TEM micrographs of various multilayers prepared for different laser light wavelengths an improvement of layer stack quality, i.e. formation of abrupt interfaces, with increasing photon energy is observed. Layer stacks having almost ideally smooth interfaces were synthesized by UV-photon ablation. HREM micrographs of these multilayers show a pronounced separation of spacer and absorber layers. The roughness sigma(R) of the interfaces between the amorphous Si- and MoSi(x)-layers was determined by image analysis. On the average a level sigma(R) approximately 0.1 nm is found. There is no indication for roughness replication or amplification from interface to interface as it is known from the appropriate products of conventional thin film technologies.