SCANNING TUNNELING MICROSCOPE IMAGES OF GRAPHITE SUBSTRATES USED IN GRAPHITE-FURNACE ATOMIC-ABSORPTION SPECTROMETRY

Scanning tunneling microscopy (STM) was used to elucidate the submicro meter defect structures on the graphite substrates used in graphite fu rnace atomic absorption spectrometry (GFAAS). Images were obtained on pristine pyrolytic coated and uncoated polycrystalline graphite tubes and on pure pyrolytic graphite platforms. For comparison, images of hi ghly oriented pyrolytic graphite, not used in GFAAS, were also obtaine d. Polycrystalline tubes were characterized by disordered surfaces wit h extensive oxidation. Pyrolytic coated tubes and pure pyrolytic graph ite platforms were characterized by scaled structures, island columns, or smoothly varying contours, Scaled structures and island columns pr esented the greatest abundance of exposed carbon edge sites and seemed probable areas for analyte reactivity and intercalation. In areas dis playing smoothly varying contours, atomic imaging revealed basal plane surface layers with moderate curvature but regular spacing between th e carbon atoms within the layers. The results imply that the weak orde ring between graphite layers along the c-axis does not preclude good a tomic ordering within the layers, and this factor may be sufficient fo r discouraging analyte-substrate interactions.