The impact of H/D substitution on the structure, composition and thermal stability of grain boundaries in sub-micron diamond films deposited on silicon

Sub-micron polycrystalline diamond films deposited using H ₂/CH ₄ gasses show Raman peaks at ~ 1130 and ~ 1470, which have been assigned to the ν ₁ and ν ₃ modes of t-PA hydrocarbons within the diamond intergranular space. Here we report the isotopic shift of these peaks in similar diamond films grown from D ₂/CD ₄ gas mixtures, as well as the splitting of the 1130 cm ^{- 1} peak to two peaks at 880 and 855 cm ^{- 1}. We suggest that this unexpected peak splitting is due to an excess of short conjugated t-PA chains and relate this to the lower amount of amorphous carbon in these deuterated films, as evidenced by Raman spectroscopy and secondary ion mass spectrometry (SIMS). This difference in grain boundary amorphous carbon content is also suggested to explain a measured difference in thermal out-diffusion of deuterium from these films, as compared to hydrogen in standard films. A third unreported Raman peak at 820 cm ^{- 1} is also examined and shown to be related to stressed SiC, seen to relax during high temperature vacuum annealing. The reduction of observed stress is partly assigned to an increase of the sp ³/sp ² ratio in the film after annealing.