ANALYSIS OF FLUOROCARBON PLASMA-TREATED DIAMOND POWDERS BY SOLID-STATE F-19 NUCLEAR-MAGNETIC-RESONANCE

In this work, solid-state F-19 NMR has been used to characterize fluorine on diamond powder surfaces after CF4 and 98% CF4/2% O2 radio-frequency plasma treatment. The fluorine surface coverage of the pure CF4 treated powder was 7.1 X 10(14) F/cm2 while the other plasma yielded a much lower coverage, 7.4 x 10(13) F/cm2. In both cases, only CF(x) (x = 1-3) functionalities were observed with the majority species being carbon monofluoride. Only 5-10% of the fluorine was bonded as CF3. With high-speed magic-angle spinning, isotropic chemical shifts were resolved and assigned relative to CFCl3 as follows: CF, 148 +/- 1 ppm; CF2, 106 +/- 2 and 123 ppm; CF3, 78 +/- 1 ppm. The peak at 123 ppm was only observed in the CF4/O2 plasma-treated sample and is speculated to be the result of atomic fluorine etching of diamond. In this sample, the loss of spectral intensity at lower chemical shifts with storage time indicates the loss or rearrangement of CF2 and CF3. NMR line shape broadening and variation in spin-lattice relaxation with decreasing temperature indicate the CF(x) groups possess some degree of motion in addition to the rotation of CF3 groups about the C3 axis. This suggests amorphous fluorocarbon deposition, since CF and CF2 on crystalline diamond surfaces are expected to be essentially static. Multiple-quantum NMR indicates that fluorine coverage is not uniform. Some fluorine is relatively dispersed on the order of approximately 5 angstrom while the remaining fluorine occurs in aggregates of greater than 40 nuclei. This is consistent with preferential deposition or reaction occurring at and around surface defects. Finally, these results may serve as a basis for reference in studying fluorine by NMR in fluorinated chemical vapor deposition diamond materials provided a sufficient amount of material is deposited.