The oxygenated phenomena of the undoped large-grain and small-grain polycrystalline diamond films

The polycrystalline diamond films in this research were deposited using a methane/hydrogen gas mixture in a microwave plasma assisted chemical vapor deposition system. Large-grain, several mu m size crystallite, diamond films and small-grain, sub-micron size crystallite, diamond films were prepared by diamond paste and diamond powder nucleation method, respectively. It is found that there is no oxygen incorporated into the diamond films during the microwave plasma chemical vapor deposition process at the synthesis temperature between 900 degrees C and 1000 degrees C. However, the oxygenated phenomena did appear for both of the large-grain and the small-grain polycrystalline diamond films after the films were exposed to air for a period of time. It was shown that the large-grain diamond films are oxygenated more than the small-grain diamond films as the samples were exposed to air for a period of time and also after the chemical cleaning treatment. It is indicated that the oxygenated phenomena of the diamond films come from two contributors, the diamond crystallite surfaces and the diamond grain boundaries. The reaction between the diamond grain boundaries and the air is fast and the oxidized dangling bonds are hard to remove. However, the oxidized dangling bonds on the diamond crystallite surfaces are gradually formed and are easily etched away by the hydrogen plasma. (C) 1998 Elsevier Science S.A. All rights reserved.