Electron and hole transmission through superconductor - normal metal interfaces

We have investigated the transmission of electrons and holes through interfaces between superconducting aluminum (Tc = 1.2 K) and various normal non-magnetic metals (copper, gold, palladium, platinum, and silver) using Andreev-reflection spectroscopy at T = 0.1 K. We analyzed the point contacts with the modified BTK theory that includes Dynes' lifetime as a fitting parameter G in addition to superconducting energy gap 2D and normal reflection described by Z. For contact areas from 1 nm^2 to 10000 nm^2 the BTK Z parameter was 0.5, corresponding to transmission coefficients of about 80 %, independent of the normal metal. The very small variation of Z indicates that the interfaces have a negligible dielectric tunneling barrier. Fermi surface mismatch does not account for the observed transmission coefficient.Comment: 9 pages, 4 figures, submitted to Proceedings of the 19th International Conference on Magnetism ICM2012 (Busan 2012

Accelerated thermal degradation of DLC-coatings via growth defects

Diamond-like carbons (DLC) are frequently used as wear protection coatings for tribologically loaded steel parts in the automotive industry. Diverse interlayer concepts are applied to increase the coatings adhesion which is otherwise poor on blank steel. Our focus lies on the influence of the adhesion layer design on the thermo-chemical stability of a H-containing DLC-coating and the significant role of growth defects. At the interfaces between individual layers or in more elaborated transition zones, several stability issues might arise under certain conditions: E.g. a thermally driven, intrinsic aging can lower the adhesion strength. With sufficiently low adhesion, stress corrosion cracking along the interface can occur, leading to delamination progression at subcritical loads