Davit Galstyan, Lars Haubold, Nina Baule, Fraunhofer USA Center Midwest, East Lansing, MI
While several studies around the usage of nitrogen-incorporated tetrahedral amorphous carbon (ta-C:N) in electroanalysis have been published, they mainly focus on ta-C:N films deposited on conductive substrates. This is due to the relatively high resistivity of ta-C:N compared to other carbon and metal-based electrodes, which without the electrically conducting substrate causes high ohmic losses when subjected to an electrical current. However, optically transparent electrodes (OTEs) are commonly carried on substrates that are insulating such as quartz or polymers. In this study we deposited 50 nm of ta-C:N by laser-arc onto insulating fused silica glass (FSG) to investigate the electrochemical response compared to the same film deposited on conductive silicon. Here we find that no oxidation or reduction of potassium ferrocyanide during cyclic voltammetry (CV) could be observed at the electrode deposited on FSG. To address this, we then introduced a 5 nm chromium (Cr) interlayer deposited by magnetron sputtering between the ta-C:N and FSG substrate. While this electrode configuration led to clear cathodic and anodic CV peaks of potassium ferrocyanide, the peak separation compared to the ta-C:N deposited on conductive silicon was increased by around 0.500 V. However, the peak separation could be reduced to values comparable to the ta-C:N deposited on conductive silicon by optimizing the Cr sputtering conditions and introducing a plasma pretreatment by a single-beam ion source. Atomic force microscopy (AFM) revealed, that these changes caused an improved Cr growth homogeneity, which in turn increases the electrical conductivity of the Cr interlayer.