SCANNING TUNNELING MICROSCOPE STUDY OF ETCH PITS ON HIGHLY ORIENTED PYROLYTIC-GRAPHITE HEATED IN AN ATOMIC-ABSORPTION ELECTROTHERMAL ANALYZER

Scanning tunneling microscopy (STM) was used to elucidate monolayer et ch pits that form on highly oriented pyrolytic graphite (HOPG) heated in an electrothermal analyzer. Pits form at elevated temperatures due to reactions between oxygen and exposed carbon edge atoms (defects) an d additionally with intraplanar carbon atoms (through abstraction). Sa mples of HOPG without analyte or matrix modifier were placed in the de pression of a pure pyrolytic graphite platform and heated by using sta ndard analysis furnace programs. Under argon stop-flow conditions, pit s form in less than a second at atomization temperatures equal to and above 1200 degrees C. With low argon pow rates (40 mL/min), pits forme d at atomization temperatures equal to and greater than 1750 degrees C in less than a second. Quantitative pit formation rates were used to indicate oxygen partial pressure, which may be as high as similar to 1 0(-3) atm at 1200 degrees C. Reaction rates were used to predict surfa ce degradation due to oxygen attack and determine that 1-mu m depth no rmal to the surface would be removed by 200 successive 5-second-period furnace firings at 1200 degrees C. Implications for increases in surf ace reactivity and analyte intercalation are discussed.