Scanning Tunneling Microscope Images of Graphite Substrates Used in Graphite Furnace Atomic Absorption Spectrometry

Scanning tunneling microscopy (STM) was used to elucidate the submicrometer defect structures on the graphite substrates used in graphite furnace 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 highly oriented pyrolytic graphite, not used in GFAAS, were also obtained. Polycrystalline tubes were characterized by disordered surfaces with extensive oxidation. Pyrolytic coated tubes and pure pyrolytic graphite platforms were characterized by scaled structures, island columns, or smoothly varying contours. Scaled structures and island columns presented the greatest abundance of exposed carbon edge sites and seemed probable areas for analyte reactivity and intercalation. In areas displaying smoothly varying contours, atomic imaging revealed basal plane surface layers with moderate curvature but regular spacing between the carbon atoms within the layers. The results imply that the weak ordering between graphite layers along the c-axis does not preclude good atomic ordering within the layers, and this factor may be sufficient for discouraging analyte—substrate interactions.