Scanning electrochemical microscopy polymerization

Such approximation is valid when the thickness of the polymeric layer is small compared to die thickness of die crystal, and the measured frequency change is small with respect to the resonant frequency of the unloaded crystal. Mass changes up to 0.05% of die crystal mass commonly meet this approximation. In die absence of molecular specificity, EQCM cannot be used for molecular-level characterization of surfaces. Electrochemical quartz crystal microbalance devices also hold promise for the task of affinity-based chemical sensing, as they allow simultaneous measurements of both tile mass and die current. The principles and capabilities of EQCM have been reviewed (67,68). The combination of EQCM widi scanning electrochemical microscopy has also been reported recently for studying die dissolution and etching of various thin films (69). The recent development of a multichannel quartz crystal microbalance (70), based on arrays of resonators, should further enhance die scope and power of EQCM. 

It is not necessary to deal with these techniques in detail here, since there are several books and monographs on the subject. The fundamental theory and practice of electrochemical and spectroelectrochemical methods can be found in [1,2] and also in [3-5], where investigations of polymeric surface layers are emphasized. Excellent monographs on EQCM [6-9] and PBD [10] are also recommended for further studies. Infrared, Mdssbauer spectroscopy, ellipsometry, etc., are described in [I I], while electron spin resonance is discussed in [12], radiotracer in [13], scanning tunneling microscopy in [14], and scanning electrochemical microscopy in [15]. The fundamentals of electrochemical impedance spectroscopy are treated in [1,2,16] however, the different models elaborated for electrochemically active films and membranes can be found in various papers (see later), while the most important methods for analyzing impedance spectra, as reported before 1994, are well summarized in [3]. Nevertheless, the essential elements of these techniques are briefly discussed here, in order to help the reader to understand the experimental material presented in this book. 

Finally, Hapiot and coworkers used scanning electrochemical microscopy (SECM) in feedback mode to investigate electronic and permeation properties of the polymeric films obtained from the mono-substituted ZnOEPfbpy)" monomer and ZnOEP monomer in the presence of free bipyridine [143]. The results showed that the polymer obtained from the EPOP process (namely from the commercial ZnOEP) was more permeable and had a lower conductivity than the one prepared using the mono-substituted ZnOEPfbpy)" monomer. These two observations were... 

---