In situ scanning probe microscopy investigations of electroactive films

Dimensional changes in electroactive films of nickel hydroxide, iridium oxide and polyaniline were investigated in situ in the electrochemical environment by scanning tunneling microscopy (STM), atomic force microscopy (AFM) and intermittent contact atomic force microscopy (ICAFM) during electrochemical oxidation and reduction. The advantages and disadvantages of the three measuring techniques are demonstrated with specific examples. While STM measurements are ambiguous due to the changing conductance of the sample during the redox process, AFM measurements on soft films such as anodic iridium oxide (AIROF) may result in surface modifications. Intermittent contact AFM (ICAFM) appears to be best suited for most samples. Shrinking of up to 40% could be observed on nickel oxide films during oxidation, which depended upon the location on the sample investigated and on the measuring technique employed. For a polyaniline film with a reversible charge capacity of 4.3 mC/cm(2) corresponding to 75 +/- 7 nm film thickness, a thickness increase of 10 +/- 3 nm was observed during oxidation.