MICROSTRUCTURAL AND MORPHOLOGICAL-CHANGES INDUCED IN GLASSY-CARBON ELECTRODES BY LASER IRRADIATION

Raman spectra, phenanthrenequinone adsorption, differential capacitance and scanning electron micrographs on fractured and polished glassy carbon (GC) surfaces were monitored before and after pulsed laser irradiation of varying power density. At power densities below 30 MW/cm2, the Raman spectra, GAMMA(PQ), C(dl)-degrees, and SEM appearance of polished surfaces changed slightly with laser activation. However, the Raman spectra of fractured GC indicated increased disorder during laser irradiation. After vigorous laser treatment, the Raman spectrum became similar to that of the polished surface, but GAMMA(PQ) and C(dl)-degrees on the fractured surface did not change greatly at power densities below 30 MW/cm2. At higher power densities, both polished and fractured surfaces showed significantly higher GAMMA(PQ) and C(dl)-degrees, and the SEMs showed evidence of local melting. After 70 MW/cm2 laser treatment, the fractured and polished surfaces were quite similar. The results support a mechanism based on thermomechanical shock below about 30 MW/cm2 and local melting above this threshold.