SCANNING TUNNELING MICROSCOPY OF CARBON SURFACES - RELATIONSHIPS BETWEEN ELECTRODE-KINETICS, CAPACITANCE, AND MORPHOLOGY FOR GLASSY-CARBON ELECTRODES

Polished, fractured, heat-treated, and laser-activated glassy carbon (GC) surfaces were examined by scanning tunneling microscopy (STM) in ambient air. Polished electrodes, as well as those which were vacuum heat treated (VHT) or laser activated (25 mW/cm2) after being polished, were comparably smooth in 2.5-mum STM scans, exhibiting root-mean-square roughness (RMSR) of approximately 4 nm. Fractured, unpolished surfaces were significantly rougher (RMSR approximately 20 nm) and exhibited numerous nodules with diameters in the range of 50-300 nm. Polished surfaces laser activated at high-power density (70 MW/cm2) showed unexpected features along polishing scratches, apparently caused by local melting. The heterogeneous electron-transfer rate constant (k-degrees, cm/s) and capacitance (C-degrees, muF/cm2) were also determined for the STM-characterized surfaces. Although rougher surfaces generally exhibited higher C-degrees, major differences in k-degrees were observed for surfaces with similar roughness and appearance. The results are consistent with the dominance of surface cleanliness in the mechanism of laser activation. Combined with past results based on adsorption, the morphological data indicate that differences in surface roughness are unimportant for laser activation of Fe(CN)64-/3- kinetics. Furthermore, the STM images reveal morphological effects of laser activation and polishing which were not apparent from previous electrochemical results.