Quantitative optical recognition of highly reproducible ultrathin oxide films in microelectrochemical anodization

Automatized microelectrochemical investigations are achieved using a scanning droplet cell. The area reproducibility for a 100 mum oxide spot is found to be better than 1%, a value typically difficult to reach even in macroscopic samples. A systematic change in color appearance is seen for oxide films with a thickness ranging from 14 to 27 nm. Analysis of optical images yields a strictly linear relation between relative transmission and anodization charge and thus allows determination of the oxide thickness with a remarkable precision better than 0.5 nm at an absolute film thickness value that is at least a factor of 20 smaller than the wavelength of light.