Evidence for trans-polyacetylene in nano-crystalline diamond films

In CVD deposited diamond films a Raman mode at approximately 1150 cm(-1) is often used as a simple criterion for a nanocrystalline diamond phase in the sample. Since this line shows a dispersion of approximately 25 cm(-1)/eV it was suggested to originate from trans-polyacetylene segments in the grain boundaries. We calculated the position of the T, mode of transpolyacetylene using a vibronic model for resonance Raman scattering and, compared the results with the measured positions of the 1150 cm(-1) mode for diamond samples on different substrates and found a very good agreement. Within the calculations we were able to estimate the mean number of uninterrupted conjugated bonds in the chains. Additionally, the response for the 1150 and 1480 cm(-1) lines turned out to be unstable vs. exposure to elevated temperatures which is further evidence for its origin from conjugated segments. (C) 2002 Elsevier Science B.V. All rights reserved.