Atomic oxygen (AO) is the main specie in the low Earth orbit (LEO) space environment, and the major hazard for carbon based materials durability and devices functionality. Chemical bonding and morphology of chemical vapor deposited (CVD) diamond films following exposure to thermal (0.04 eV) and hyper-thermal (~5 eV) atomic oxygen (AO) were studied using high resolution electron energy loss spectroscopy (HREELS), near edge x-ray adsorption fine structure (NEXAFS) and atomic force microscopy (AFM).

HREELS measurements reveal that exposure to AO results in a very reactive surface that upon exposure to ambient conditions facilitates adsorption of adventitious hydrocarbons on the diamond surface, upon annealing most of this content is removed, and the diamond spectral features are partially restored. Furthermore, hydrogen is removed from the diamond surface upon exposure to AO. NEXAFS measurements of C1s pre-edge structure of diamond films also reveal features related to adsorbed species.

AFM study of polycrystalline CVD diamond film morphology following exposure to thermal AO reveals only subtle smoothing of edges and terrace-like features on the diamond facets structure. Hyper-thermal AO exposure results in a selective etching: (111) oriented facets are severely etched, while (100) oriented facets show high endurance. The observed phenomenon is associated with the AO chemisorption energies on the various diamond facets. Only facets having AO chemisorption energy lower then that of the impingent hyper-thermal AO will be etched. Hyper-thermal AO is the major hazard for carbon-based materials in the LEO space environment; therefore, highly durable materials for space applications can be produced utilizing diamond directional growth.