Thermal desorption of hydrogen and various hydrocarbons from graphite bombarded with thermal and energetic hydrogen

Abstract The thermal release of hydrogen (deuterium) and hydrocarbons has been investigated after exposing pyrolytic graphite to thermal and energetic hydrogen under various conditions. After exposing graphite to thermal hydrogen atoms, the retained hydrogen desorbs in the subsequent heating in two different desorption processes whereby the radical CH 3 , C 2 H x and C 3 H x species desorb together with the hydrogen molecule in the first desorption process. Absolute amounts of the hydrocarbons formed reach about 0.25 of the amount of desorbed H 2 and follow a similar fluence dependence as the H 2 desorption. The simultaneous bombardment of the graphite surface with energetic inert ions (Ar − ) and with thermal hydrogen atoms increases the retention of hydrogen and changes the desorption spectrum of the hydrogen whereas the hydrocarbon desorption spectrum remains unchanged. In the case of bombarding graphite with energetic hydrogen ions (investigated for E H > 350 eV ) the desorption of C 2 and C 3 type hydrocarbons is negligible compared to that of methane. The methane desorption itself is characterized by a sharp fluence dependence and by the formation of CH 4 molecules.