Microstructure of ultrananocrystalline diamond films grown by microwave Ar-CH4 plasma chemical vapor deposition with or without added H-2

Ultrananocrystalline diamond (UNCD) films, grown using microwave plasma-enh anced chemical vapor deposition with gas mixtures of Ar-1%CH4 or Ar-1%CH4-5 %H-2, have been examined with transmission electron microscopy (TEM). The f ilms consist of equiaxed nanograins (2-10 nm in diameter) and elongated twi nned dendritic grains. The area occupied by dendritic grains increases with the addition of H-2. High resolution electron microscopy shows no evidence of an amorphous phase at grain boundaries, which are typically one or two atomic layer thick (0.2-0.4 nm). Cross-section TEM reveals a noncolumnar st ructure of the films. The initial nucleation of diamond occurs directly on the Si substrate when H-2 is present in the plasma. For the case of UNCD gr owth from a plasma without addition of H-2, the initial nucleation occurs o n an amorphous carbon layer about 10-15 nm thick directly grown on the Si s ubstrate. This result indicates that hydrogen plays a critical role in dete rmining the nucleation interface between the UNCD films and the Si substrat e. The relation between diamond nuclei and Si is primarily random and occas ionally epitaxial. (C) 2001 American Institute of Physics.