Raman Spectroscopy and TEM of Long Linear Carbon Chain Formed in CNT Field Emission Cathode

Long linear carbon chains (LCCs) encapsulated in carbon nanotubes (CNTs) were produced on a film scale by field emission discharge of CNT films. LCCs inside CNTs were characterized by Raman spectroscopy and transmission electron microscopy. After an electric discharge of a CNT film cathode, long LCCs encapsulated in single-wall CNTs as well as double-wall and triple-wall CNTs were formed in the film. The length of LCCs is longer than 30 nm (i.e., more than 230 carbon atoms). Not only a single LCC but also two or three LCCs in parallel inside a CNT were found. Raman spectra showed prominent peaks, called "LCC bands", in a region from 1790 to 1860 cm(-1) originating from longitudinal optical phonons of LCCs. The observation of strong LCC bands are due to resonance Raman scattering, i.e., the excitation photon energies between 1.85-2.54 eV match with energy gaps of the long LCCs inside CNTs.