Correlation between the sp2-phase nanostructure and the physical properties of unhydrogenated carbon nitride

Abstract

Spectroscopic analysis of a -C and a -CN x films prepared by ultrafast high repetition rate pulsed laser deposition J. Appl. Phys. 97, 073522 (2005); 10.1063/1.1874300 Effects of thermal annealing on the structural, mechanical, and tribological properties of hard fluorinated carbon films deposited by plasma enhanced chemical vapor deposition This paper consists of an investigation of the structural arrangement of the sp 2 phase in amorphous unhydrogenated carbon nitride ͑a-CN x ͒ films and its effect on their physical properties. The a-CN x films ͑0.16Ͻ x Ͻ 0.25͒ were synthesized using a hybrid deposition system combining laser ablation of graphite and a source of atomic nitrogen. The microstructure of the films was investigated by Raman spectroscopy and electron paramagnetic resonance ͑EPR͒, while their optical and mechanical properties were determined by spectroscopic ellipsometry and nanoindentation, respectively. It was found that deposition at high laser intensities leads to an increase in the spin density ͑Ͼ10 20 /cm 3 ͒ and the EPR linewidth ͑of a few gausses͒ along with a decrease in nitrogen content. Visible Raman measurements indicate that these effects are accompanied by an increase in the degree of disorder of the sp 2 phase, as inferred from the broadening and downshift of the G Raman band, and a reduction of the CN triple bond signal. The analysis of these results in terms of the structural configuration and bonding in the films, show that an enhancement of the connectivity of the sp 2 phase in the layers, takes place when deposition is performed at high laser intensities. These structural modifications are strongly correlated to a decrease in the optical gap from 0.61 to 0.21 eV as well as to an increase of the hardness value of the films from 12 to 24 GPa. The transition from a reduced to an enhanced connectivity of the sp 2 phase occurs when the nitrogen content decreases below 22 at. %, as a result of the detected reduction of the triply bonded CN species in the layers.

Impact of the annealing temperature on Pt/g-C 3 N 4 structure, activity and selectivity between photodegradation and water splitting

“….003 is coherent with previous literature findings. Most of the literature agrees that with such a g value and the absence of the typical hyperfine splitting expected from nitrogen; the EPR signal in carbon nitride polymers is likely to arise from unpaired electrons preferentially localized on carbon atoms [10,17,18]. However, a study based on solid state NMR and EPR shows that nitrogen located electron should not be ruled out, as electron delocalization could explain the absence of hyperfine splitting [19].…”

Template-free synthesis of porous graphitic carbon nitride microspheres for enhanced photocatalytic hydrogen generation with high stability

“…Thus, the sample was characterized by the electron paramagnetic resonance (EPR) to determine the structural defects. As shown in Fig S4, the EPR spectrum of CNMS-550 shows a strong signal at g value of 2.003 for the delocalized electrons in the conduction band as compared to the bulk g-C 3 N 4 and CNMS [16,42], indicating that the existence of trapping states or defects on the CNMS-550 sample.…”

Textural and electronic structure engineering of carbon nitride via doping with π-deficient aromatic pyridine ring for improving photocatalytic activity

“…6. Only one single Lorentzian line centered at a g value of 2.0034 both in dark and visible light irradiation are observed for the CN and CN-DPY 0.07 samples [32], demonstrating a well-established CN semiconductor structure even for the pyridine-doped samples. These Lorentzian lines originate from the unpaired electron on the carbon atoms of the aromatic rings within -bonded nanosized clusters.…”