Scanning tunneling microscopy of carbon surfaces: relationships between electrode kinetics, capacitance, and morphology of 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/[cm.sup.2]) after being polished, were comparably smooth in 2.5-[micro]m STM scans, exhibiting root-mean-square roughness (RMSR) of '4nm. Fractured, unpolished surfaces were significantly rougher (RMSR '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/[cm.sup.2]) 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],[micro]F/[cm.sup.2]) 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).sup.6][.sup.4-/3-] kinetics. Furthermore, the STM images reveal morphological effects of laser activation and polishing which were not apparent from previous electrochemical results.
The utilizaton of scanning tunneling microscopy for studying various standard pretreatment procedures for gas chromatography (GC) electrodes is discussed. Correlations on the surface morphology and electrochemical activity characteristics of conventionally polished, laser irradiated, fractured and vacuum heat treated GC surfaces were conducted. Results indicate that surface roughening is not the only cause for the increase in electrode activity.