A similar temperature-dependent hysteresis in O and CO product flux has also been observed in our earlier studies of the oxidation of vitreous carbon , and it has been discussed in detail in the context of the more recent study that employed a continuous and high-flux beam of oxygen atoms . The basic explanation is likely the same for the oxidation of FiberForm. The temperature-dependent hysteresis may arise from the intercalation of oxygen atoms between graphitic planes, which desorb as O, O2, or CO at high temperatures on the time scale of minutes to hours. The energy-barrier dependence of CO formation on oxygen coverage could also play a role. Consider a carbon material (FiberForm or vitreous carbon) initially at a high surface coverage.