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Narrow Ge layers embedded in Si are investigated using photoluminescence (PL) spectroscopy. With increasing layer thickness a growth mode changeover from two-dimensional (2D) strained-layer growth to three dimensional Stranski–Krastanov growth is observed. Additional PL lines that are redshifted with respect to the PL signal of the 2D strained layers are attributed to islands formed by three-dimensional growth. The occurrence of these new lines is accompanied by a blueshift of the PL of the 2D layers, indicating a strong Ge diffusion from the 2D layers towards the islands.

The use of magnesium and its alloys as biodegradable metallic implant materials requires that their corrosion behavior can be controlled. We tailored the Mg release kinetics and cell adhesion properties of commercially pure Mg by chemical surface treatments in simulated body fluid, in Dulbecco's Modified Eagle's cell culture medium in the presence or absence of fetal bovine serum (FBS), or in 100% FBS. HeLa cells were cultured for 24 h on these Mg surfaces to characterize their biocompatibility. Cell density on all treated surfaces was significantly increased compared with a polished Mg surface, where almost no cells survived. This low biocompatibility of pure Mg was not caused by the high Mg ion release with concentrations of up to 300 mg/L in the cell culture medium after 24 h, as cells grown on a glass substrate showed no adverse reactions to high Mg ion concentrations. Rather, the most critical factor for cell adhesion was a sufficiently reduced initial dissolution rate of the surface. A comparison among all surface treatments showed that an incubation of the Mg samples in cell culture medium gave the lowest dissolution rate and resulted in the best cell adhesion and spreading behavior.

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