Correlation between ion-flux and microstructure of a-C:H films

a-C:H layers prepared at different ion energies have been characterised by several methods such as13C-NMR, EELS and ESR. With increasing ion energies from 30 eV to 170 eV, the sp2 fraction of the samples rises from 27% to about 60% and the spin density increases by more than one order of magnitude due to less incorporation of hydrogen into the film. Simulaneously, the linewidth of the ESR signal becomes narrower. This can be interpreted as an increasing cluster size from single benzene rings to 3 or 4 fused 6-fold rings. Measurements of the ion energy distribution (IED) of the positive ion flux to the substrate surface indicate a saddle-shaped peak structure typical of a resistive plasma sheath. Mass spectra of the ion flux can be correlated, to a certain degree, to the appearance potentials of electron-molecule and ion-molecule collisions.