Electronic states of trans-polyacetylene, poly(p-phenylene vinylene) and sp-hybridised carbon species in amorphous hydrogenated carbon probed by resonant Raman scattering

摘要

Inclusions of sp-hybridised, trans-polyacetylene [trans-(CH)x] andpoly(p-phenylene vinylene) (PPV) chains are revealed using resonant Ramanscattering (RRS) investigation of amorphous hydrogenated carbon (a-C:H) filmsin the near IR - UV range. The RRS spectra of trans-(CH)x core Ag modes and thePPV CC-H phenylene mode are found to transform and disperse as the laserexcitation energy \hbar{\omega}L is increased from near IR through visible toUV, whereas sp-bonded inclusions only become evident in UV. This is attributedto \hbar{\omega}L probing of trans-(CH)x chain inhomogeneity and thedistribution of chains with varying conjugation length; for PPV to the resonantprobing of phelynene ring disorder; and for sp segments, to \hbar{\omega}Lprobing of a local band gap of end-terminated polyynes. The IR spectra analysisconfirmed the presence of sp, trans-(CH)x and PPV inclusions. The obtained RRSresults for a-C:H denote differentiation between the core Ag trans-(CH)x modesand the PPV phenylene mode. Furthermore, it was found that at various laserexcitation energies the changes in Raman spectra features for trans-(CH)xsegments included in an amorphous carbon matrix are the same as in bulktrans-polyacetylene. The latter finding can be used to facilitateidentification of trans-(CH)x in the spectra of complex carbonaceous materials.