Gas-phase thermodynamic models of nitrogen-induced nanocrystallinity in chemical vapor-deposited diamond

Gas-phase thermodynamic equilibrium calculations involving H-2/CH4/N-2 mixtures were performed to investigate the chemical interactions leading to nitrogen-induced nanocrystallinity in microwave plasma chemical vapor deposition of diamond films. The strong influence of the CN radical in causing nanocrystallinity is confirmed by the correlation of its modeled composition in the gas phase with the degree of nanocrystallinity as determined experimentally for diamond films grown with different N-2 additions. For a given CH4 feedgas concentration, there exists a critical N-2 feedgas concentration, above which the change in the CH3/CN ratio is minimal and further induced nanocrystallinity is diminished. This is verified experimentally where it is observed that the same critical N-2 feedgas concentration exists, above which a further decrease in diamond crystallinity and surface roughness of the grown diamond films is minimal. (C) 2002 American Institute of Physics.