Valence band electronic structure of carbon nitride from x-ray photoelectron spectroscopy

This article reviews the valence band (VB) electronic structure of carbon nitride and reports on results obtained from carbon nitride films prepared by pulsed laser deposition (PLD). In the present work, two series of carbon nitride films have been synthesized by nitrogen-ion-beam-assisted PLD and reactive PLD in nitrogen atmosphere, respectively. X-ray photoelectron spectroscopy (XPS) is applied to determine the VB electronic structures. XPS VB spectra reveal that the electronic structures of the prepared carbon nitride films depend on nitrogen supply manner. In the case of nitrogen-ion-beam-assisted deposition, four bands in the regions ∼0–6.2, ∼6.2–13.7, ∼13.7–20.8, and ∼20.8–30 eV are clearly observed in the VB electronic structure, which stem from C 2p electrons associated with π bonds and sp2N in a planar graphite structure, C 2p and N 2p electrons associated with σ bonds, a mixture of 2s and 2p electrons, and C 2s and N 2s electrons, respectively. For the films deposited by reactive PLD in a nitrogen atmosphere at room temperature, a new band that results from N lone pairs of β-C3N4 structure appears at ∼5 eV in region ∼1.0–7.4 eV, instead of the band at ∼2.3 eV in region ∼0–6.2 eV in the case of nitrogen-ion-beam deposited films. At elevated deposition temperature, the evolution of carbon nitride films towards amorphous carbon structure is observed. Furthermore, both nitrogen content and substrate temperature have a strong influence on the VB electronic structures of carbon nitride films. The evolution of VB electronic structure is also discussed by relating to the XPS core-level spectra of the carbon nitride films.