Thermogravimetric analysis of the oxidation of CVD diamond films

Diamond films grown by microwave plasma assisted chemical vapor deposition (CVD) were studied by thermogravimetric analysis under an air atmosphere. Oxidation rates were measured between 600 and 750 °C to determine an activation energy of 213 kJ/mol which is similar to that reported for natural diamond. The rate of oxidation increases with increasing surface area and decreases with increasing humidity. The oxidation proceeds by etching pits into the film, creating a highly porous structure. Graphitization was not detected in partially oxidized samples by Raman or Auger electron spectroscopy. A film that was heated to 1170 °C under nitrogen remained IR transmissive.