Two-dimensional wide-line separation (WISE) NMR spectroscopy has been applied to obtain structural correlation in fluorocarbon films deposited via a pulsed plasma enhanced chemical vapor deposition. Films from two pulsed deposition conditions, 10/20 and 10/400 ms on/off times, were analyzed in detail. One-dimensional 19F and 13C NMR results agreed well with prior studies of these films using X-ray photoelectron spectroscopy, which showed greater CF2 fractions with decreasing pulsed deposition duty cycle. 13C CPMAS studies, in addition, distinguished between unsaturated and saturated fluorocarbon species in these films. However, 19F-13C WISE allowed further differentiation of fluorocarbon moieties by the difference in nearest-neighbor connectivity. The 10/20 film showed a prevalence of at least two inequivalent CF3 species. A weak presence of unsaturated =CF- species was also detected. No specific CF2 moiety was resolved, which was attributed to significant chemical shift dispersion and heterogeneity in CF2 bonding environment. In contrast, the 10/400 film displayed an increased proportion of CF2 species, predominantly as -CF2CF2- and CF3CF2- groups and less CF3 termination, indicative of a structure approaching that of poly(tetrafluoroethylene). These observations support the hypothesis of a less aggressive deposition environment, inducing less cross-links and unsaturation and promoting linear chain propagation, with a longer pulse off-time during deposition. Spinning sideband patterns in the 19F dimension of NMR spectra did not severely hinder spectral interpretation but instead offered a means of revealing motional differences in the fluorocarbon moieties.
All Science Journal Classification (ASJC) codes
- Physical and Theoretical Chemistry
- Surfaces, Coatings and Films
- Materials Chemistry