Study of nanocarbon thin-film field-electron emitters by Raman spectroscopy

Raman spectroscopy was used to study the features of the electron-phonon interaction in thin carbon films that are capable of low-field emission of electrons. It was found that in the Raman spectra of samples with this ability the characteristic peaks of carbon were almost completely suppressed, and also a wide photoluminescence band could be present. At the same time, the Raman spectra of non-emitting samples had the form typical of graphite-like carbon spectrum. This observation is in accordance with the two-barrier model of low-field electron emission from thin films of considered type, corresponding to which their emissive capability is maintained by the presence of hot electrons. Thus, in thin films consisting of numerous isolated carbon islands (nanoclusters) the extraction of electrons into the vacuum is facilitated by prolonged hot electron lifetime. Such prolongation, in turn, can be associated with the suppression of electron-phonon interactions by the spatial confinement effect. Consequently, it should result in the decrease of prominent bands in Raman spectra which are originated by electron-phonon interactions, while the photoluminescence intensity may, on the contrary, rise. Particularly such deformations of the Raman spectra were observed in the present study.