A systematic study of the chemical bonding and morphology of the diamond surface following interaction with atomic oxygen was undertaken. Hot Filament - CVD diamond films with sub-micron grain size have been exposed to either MW hydrogen plasma, or to oxygen RF plasma etching for 5 hours. The RF plasma exposed films were annealed in-situ at various temperatures up to 800°C. After annealing, the surface was exposed in-situ to thermally activated hydrogen in order to assess surface regeneration mechanism.
High Resolution Electron Energy Loss Spectroscopy (HREELS) was used to evaluate the surface bonding states, while X-ray Photoelectron Spectroscopy (XPS) yielded the oxygen atomic concentration and complementary information about chemical bonding. Force Modulation - Atomic Force Microscopy (AFM) measurements were used to visualize surface morphology and to identify the preferential etching sites. This method was shown to provide both enhanced resolution and surface elasticity images.
XPS and HREELS measurements were carried out after annealing to 315°C, 600°C and 800°C. HREELS of the oxygen plasma exposed surface revealed OH related vibrational modes, while the diamond C-C overtone was not visible. After a short annealing of the oxygen plasma treated film to 315°C, the diamond C-C overtone emerges, concurrently with a reduction of OH related peaks. The annealing process resulted also in changes in the sp2-bonded carbon content in the near-surface layer. Thus, HREELS results allow to elucidate the question of where does oxygen bond as a result of plasma-surface interaction.
Force Modulation-AFM measurements indicated that exposure to atomic oxygen resulted in preferential etching of the grain boundaries on the diamond surface. This is in comparison to AFM measurements of pristine and MW hydrogen plasma treated samples that show well-pronounced grain boundaries between the diamond facets on the surface.
The correlation between AFM, HREELS and XPS results allow better understanding of the diamond-oxygen interaction mechanism, as well as diamond surface reactivity and morphology. Studies of the interaction of CVD diamond with atomic oxygen are important for the basic understanding of its durability in harsh conditions, such as the low Earth orbit space environment.
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