Investigation of Stability and Degradation Mechanism of the Germanium-Carbon Coatings in Salt Fog Environment

In the current study, the Ge1-xCx coatings were deposited on silicon and glass substrates by a plasma enhanced chemical vapor deposition (PECVD) process with a gas mixture of GeH4 and CH4 as the precursors. In order to evaluate the environmental stability of the coatings, the salt fog test was used. Microstructural investigation and bonding characterization of coatings were performed using a field emission scanning electron microscope (FESEM) equipped with energy dispersive spectrometer (EDS) and X-ray photoelectron spectrometer (XPS), respectively. After 24 hours exposure to the salt fog, all of the germanium-carbon coatings are deposited under different conditions shows a very good stability; So that, there was no trace of detachment, peeling, cracking and blistering on the specimens. Scanning electron microscopic evaluations from the surface of the coatings also confirmed this. Only for the carbon-rich Ge1-xCx coatings, some parts of the edges of the coating were degraded. The mechanism of degradation of the coatings was described as blistering and crack development due to the influence of water molecules on the interface of the coating/substrate.