In Situ Characterization of Electrochemical Polymerization of Methylene Green on Platinum Electrodes

A novel in situ characterization technique using imaging ellipsometry in conjunction with cyclic voltammetric (CV) deposition has been applied to correlate polymerized methylene green (poly-MG) film thickness and morphology, with charge transferred during CV cycles. We also report values for the refractive index (n) and extinction coefficient (k) of the monomer solution and the poly-MG film, for the first time. These values have been derived from measurements that employ multiple angles of incidence in the ellipsometry and analysis using an optical model based on Fresnel theory. The in situ characterization of film growth with thickness progression provided comprehensive information on the deposition process that could not be obtained using ex situ techniques such as scanning electron microscopy or optical microscopy. The results demonstrate the value of imaging ellipsometry as a quantitative characterization technique to monitor polymer film growth in situ and to characterize the quality of the film in terms of surface morphology and homogeneity as a function of film thickness. Comment is also provided on how the technique can be combined with other characterization techniques to deliver a more comprehensive analysis and control of the electrochemical deposition process.