Elektrochemische Untersuchungen zur Porosität von Nanoschichten auf Kohlenstoff-Basis

The porosity of different carbon-based thin films was measured and compared using cyclic voltammetry. The coatings werde deposited onto an iron substrate and the dissolution current density of the substrate material through the pores in the protective film was measured in a corrosive aqueous medium. The deposition methods were the following: thermal evaporation followed by ion bombardement, plasma activated chemical vapourphase deposition and vapourphase polymerization. The composition, structure und thickness of the coatings were characterized with Raman-spectroscopy, secondary ion mass-spectrometry, scanning electron microscopy and a profilometer. The influence of various deposition parameters on the film porosity could be investigated via the measured current-potential-plots. It could be shown that for most thin film systems the porosity decreased with increasing film thickness but above a certain thickness the coatings become instable and the film surface gets cracks because of intrinsic stress. Only for the polymer films of poly(p-xylylene) coatings could be deposited free from pores above a film thickness of 700 nm. Additionally from the measured shifts in the open circuit potentials a theory was developed which explains the potential shifts and can give additional, complementary information about the shape of the pores in the film.