The mystery of the 1140 cm−1 Raman line in nanocrystalline diamond films Original Research Article

A strong and distinct Raman peak around 1140 cm−1 is often taken as a simple criterion for a nanocrystalline diamond phase in deposited diamond films. However, the observation that (i) this mode is always accompanied by a mode around 1480 cm−1 (seen around 1490 cm−1 as a shoulder of the G-mode), (ii) both of these modes show (similar) dispersions while the diamond mode around 1332 cm−1 does not, and (iii) these both modes vanish after thermal annealing but the diamond mode not, made this assignment doubtful. By performing a thin film preparation with deuterium and H–D substituted hydrocarbon sources we provide direct evidence that these two modes originate from trans-polyacetylene in the diamond film.