Kinetics and mechanism of oxidation of basal plane on graphite

摘要

The kinetics and mechanism of oxidation of carbon atoms exposed at monolayer steps on graphite surface have been studied with the etchhyphen;decoration and transmission electron microscopy technique and two pieces of direct evidence are shown for the importance of surface diffusion in the overall kinetics. It is found that the rate of carbon removal, or the turnover frequency, depends on the population density of these edge carbon atoms, being substantially higher on lowhyphen;density surfaces. In the argon flush experiment, it is found that surfaces with low edge carbon densities continue to rsquo;rsquo;burnrsquo;rsquo; for prolonged periods of time after O2is cut off from the gas phase. Two independent mechanisms are revealed by the experimental results: (1) reaction resulted from direct collision of O2on the edge carbon, and (2) reaction of the edge carbon with the migrated oxygen which is first chemisorbed on the basal carbon. Furthermore, from the results of the argon flush experiments, the following results can be calculated: surface diffusion coefficientthinsp; = 5times;10minus;12cm2/s (for O/C = 0.34) and 2times;10minus;12cm2/s (for O/C = 0.06); rate constant for the edge carbon reacting with the migrated O atomthinsp; = 4.5 sminus;1, all at 650thinsp;deg;C. The amount of chemisorption on the basal plane can also be obtained from the data of the argon flush technique as demonstrated in this work.