Influence of Different Carbon Structures on Diamond Synthesis by Chemical Vapour Deposition

Structurally different carbon films selectively generated at the surface of glassy carbon, titanium, and silica glass substrates are tested as nucleating layers for diamond synthesis by hot filament chemical vapour deposition (HFCVD). Before the CVD process, the substrates are treated in different ways in order to produce carbonaceous surface layers with specific structures. On glassy carbon specimens, surface structural modifications are induced by pulsed ruby laser irradiation (λ = 694.3 nm, energy density in the range 100 to 500 mJ/cm2). The polycrystalline titanium and silica glass substrates are conversely precoated with amorphous carbon layers produced by electron beam irradiation. The structural analysis of the modified substrate surfaces and of the CVD deposits is performed by means of reflection high energy electron diffraction (RHEED) and electron energy loss spectroscopy (EELS). The effects due to both structure and thickness of the various carbon layers on the CVD synthesis of the diamond phase are discussed.