Bulk and surface-enhanced Raman spectroscopy of nitrogen-doped ultrananocrystalline diamond films

摘要

Ultrananocrystalline diamond films (UNCD) grown in an Ar-rich microwave plasma with nitrogen gas added in amounts of 0-25% were studied by Raman spectroscopy using 514.5 and 413.1 nm laser excitation. Besides the Raman spectra of diamond, the first and second order Raman scattering of disordered graphite and polyacetylene were detected and analyzed for samples with different nitrogen content. With surface enhanced Raman scattering (SERS) a variety of surface vibrational modes was observed: (ⅰ) CH_x stretching vibrations of sp~3 and sp~2 hybridized carbon in the range of 2800-3100 cm~(-1); (ⅱ) the sp~2 and sp~1 hybridized CC(CN) stretching modes in the range of 1600-2300 cm~(-1); and (ⅲ) lines in the range of 200-1250 cm~(-1) related to different kinds of vibrations of substituted aromatic rings. These results indicate that in N-doped UNCD films the intergrain material is a well connected mixture of predominantly sp~2 phase with some amount of sp~1 phase of carbon and nitrogen that is suggested to provide high electrical conductivity.