|M.Sc Student||Anastasia Gaisinskaya|
|Subject||Morphology and Chemical Composition of Single Crystal|
Diamond Surfaces Studies by Atomic Force
Microscopy and Electron Spectroscopy
|Department||Department of Chemistry||Supervisor||Full Professor Hoffman Alon|
|Full Thesis text|
Two types of natural single crystal (100) oriented diamond type 2a surfaces were examined for morphology and chemical composition before and after microwave hydrogen (MW-H) plasma exposure. The two surfaces under the examination were (i) mechanically polished and (ii) laser cut.
The current research has demonstrated that exposure of polished single crystal diamond surfaces to MW-H plasma at optimized conditions may be applied as an efficient method for the smoothing out of single crystal diamond surfaces. Under appropriate plasma exposure conditions the diamond surfaces smooth out as reflected in the decrease in the number and depth of the polishing scratches. However, adverse effects on the surface morphology through the formation of pits were found to occur upon long exposure times and high plasma power. The morphology of the laser cut surface showing ill-defined laminar structure without any characteristic features was not significantly affected by subsequent MW-H plasma exposure. This is in contrast to the polished surfaces for which exposure to the MW-H may results in its planarization under optimized conditions.
X-ray photoelectron spectroscopy examination shows that after laser cutting under ambient condition the upper surface of a diamond is a heavy oxidized layer consisting of a variety of carbon-oxygen chemical states comprising --C=O, --C-O-C-- and --C-O-H species. The thickness of the oxide layer was estimated to be ~22 Ǻ. Upon vacuum annealing to 700 ºC the thickness of the oxide layer decreases to ~10 Å and the upper surface layer becomes more diamond-like through desorption of C~O species. Exposure of the laser cut diamond surface to a MW-H plasma results in removal of the oxide layer and exposure of the diamond phase. Current research shows that the surface chemical composition and thermal stability of the laser cut and polished surfaces both after MW-H exposure are nearly similar.
High resolution electron energy loss spectroscopy was used to determinate different chemical bonding configurations present on the grown single crystal diamond (100) surface and their thermal stability induced by vacuum annealing. In-situ hydrogen terminated surfaces were oxidized by exposure to thermally activated oxygen. It was determined that gradual annealing leads to the removal of oxygen containing species and to the regeneration of hydrogenated diamond surface. There was no indication of hydroxyl group after the oxygen exposure. Possible chemical processes involving activated hydrogen and oxygen during the exposures and subsequent annealing are suggested.