FOURIER-TRANSFORM RAMAN-SPECTROSCOPIC AND SCANNING ELECTRON-MICROSCOPIC STUDIES OF CHEMICAL-VAPOR-DEPOSITED DIAMOND-LIKE CARBON-FILMS

A combined study based on scanning electron microscopy and Fourier transform Raman spectroscopy is presented for different kinds of diamond films. These films were obtained by the hot filament chemical vapor deposition (HFCVD) technique with both silica (SiO2) and silicon (Si) being used as substrates. CVD diamond films, having crystallite dimensions larger than about 1 mum (the wavelength for Raman excitation being 1.06 mum with an Nd:Yag CW laser), show tetrahedral chemical bonding and single-crystal structural features being characterized by the appearance of the sharp first-order 1330 cm-1 Raman line characteristic of natural or high-pressure synthetic diamonds. Films having crystalline dimensions < 0.1 mum still exhibit tetrahedral (sp3) bonding. For such small crystals, the wavevector conservation rule for Raman spectroscopy of single crystals of diamond breaks down and only broad features, with the most intense Raman lines falling in the range 1260-1100 cm-1, are observed. This broad feature is characterized by some additional superimposed sharp lines, the maxima of which vary from sample to sample, showing the effect of overlap of spectra from various domain sizes of the crystallites, edge effects and contribution from other forms of non-diamond carbon. The crystalline diamond peak observed at 1330 cm-1 indicates that the diamond structure, at the temperature of synthesis, is retained in these films, and the large width of the Raman peak is probably due to the presence of defects. The main low-wavenumber peaks observed in all spectra obtained with 1.06 mum excitation are interpreted as arising from the amorphous disordered sp3-bonded carbons, which are formed as precursors to the crystalline diamond grown by the HFCVD technique.