Photoelectron-spectroscopy study of amorphousa-CNx:H

Abstract

We report in situ x-ray photoemission, ultraviolet photoemission (UPS), and electron-energy-loss photoelectron-spectroscopy studies of the electronic structure of nitrogen-containing amorphous hydrogenated carbon (a-CN:H). Films with different nitrogen concentrations are prepared by the ion-beamdeposition technique. The photoemission measurements do not reveal a shift in the Fermi level with respect to the top of the valence band, as would be expected from an n-type nitrogen-doping mechanism proceeding via substitution. The C 1s core-level shifts observed as a function of nitrogen content are identified as chemical in nature, and the variation in line shape and peak position is explained in terms of a two-phase superposition model. A simple model fit to the He I UPS valence-band spectra reveals the effects of nitrogen on the spectral shape. It illustrates, in particular, the sensitivity of the partial p-m density of states (DOS) to the presence of nitrogen, and confirms the role played by the m bonds in controlling the electronic structure of a-C:H. The observed increases in area and width of the p-~DOS with increasing nitrogen content are in line with an existing model which favors a defect density increase and a size increase of the graphitelike islands formed by the clustering of m. states in aromatic rings.

Surface energy of the plasma treated Si incorporated diamond-like carbon films

“…It indicates that the surface structure has become more graphitized with nitrogen incorporation into the surface. Mansour and Ugolini have also observed that nitrogen incorporation in amorphous hydrogenated carbon films favors graphitization [42]. From He I UPS valence band spectra, they noted increase in area and width of the p − π density of states (DOS) with increasing nitrogen content which is in accordance with the increase in size of the graphite like island due to clustering of π states in the aromatic rings.…”

Composition and chemical bonding of pulsed laser deposited carbon nitride thin films

“…We would like to underline that our interpretation of the components of the N 1s and C 1s core level lines is coherent with the values of the binding energies ͑BE͒ of reference organic polymers containing nitrogen. Pyridine ͑CvN, sp 2 hybridization͒ has a C 1s BE at 285.5 eV 17,[25][26][27] and a N 1s BE at 400.6 eV. [25][26][27] Urotropine or HMTA ͑C-N, sp 3 hybridization͒, exhibits a C 1s BE at 286.9 eV ͓287.3 eV for hexamethylenetetramine ͑HMTA͔͒ 17,28-30 and a N 1s BE at 399.4 eV.…”

“…Pyridine ͑CvN, sp 2 hybridization͒ has a C 1s BE at 285.5 eV 17,[25][26][27] and a N 1s BE at 400.6 eV. [25][26][27] Urotropine or HMTA ͑C-N, sp 3 hybridization͒, exhibits a C 1s BE at 286.9 eV ͓287.3 eV for hexamethylenetetramine ͑HMTA͔͒ 17,28-30 and a N 1s BE at 399.4 eV. The deconvoluted peaks from the C 1s spectra at Ϸ287 eV ͑C1͒ and from the N 1s spectra at Ϸ399 eV ͑N1͒ could also be assigned to CwN bonds 16,18,26,31 but the binding energy of the peak C1 in both the samples ͓Figs.…”

Nitrogen modification of hydrogenated amorphous carbon films

“…Interestingly, they observed that nitrogen was able to increase the conductivity of a-C:H, and this has since been repeated by numerous other groups. [4][5][6][7][8][9][10] However, it has been unclear whether N increased the conductivity by doping-raising the Fermi level towards the conduction band, or by graphitization of the bonding-narrowing the band gap.…”