Photoelectron emission and Raman scattering studies of nitrogenated tetrahedral amorphous carbon films

Abstract

Structure of nitrogenated carbon films prepared from acetylene and nitrogen mixture in electron cyclotron resonance plasmaNitrogenated tetrahedral amorphous carbon ͑N:ta-C͒ films prepared by the filtered cathodic vacuum arc technique were studied by x-ray photoelectron spectroscopy ͑XPS͒, Raman spectroscopy, spectroscopic ellipsometry, ultraviolet photoelectron spectroscopy and temperature dependent resistance measurement. As the nitrogen flow rate varies from 0 to 20 sccm, the nitrogen content in the deposited film increases from 0 to 4.6 at. %. Curve fitting of the C 1s and N 1s XPS spectra shows that the C-C sp 3 fraction decreases with an increase in nitrogen content and that the nitrogen atoms are mainly bonded in sp 2 C-N bonds. The pure ta-C film has a work function of 4.35 eV and the N:ta-C films have a value around 4.55 eV. With an increase in nitrogen flow rate, the intensity ratio of the D peak to the G peak, I D /I G increases monotonously from 0.44 to 1.25 and the G peak width decreases from 220 to 199 cm Ϫ1 . The Tauc optical band gap decreases from 2.2 to 1.8 eV.

Amorphous hydrogenated carbon-nitride films prepared by RF-PECVD in methane–nitrogen atmospheres

“…An increase in the nitrogen incorporation for increasing N 2 /CH 4 ratios is observed which saturates for higher N 2 /CH 4 ratios. Similar results have been reported for material grown in FCVA system [4] and Electron Cyclotron Wave Resonance [5]. The maximum N/C value obtained is well bellow the 1.33 expected for theoretical C 3 N 4 [3,5].…”

“…Similar results have been reported for material grown in FCVA system [4] and Electron Cyclotron Wave Resonance [5]. The maximum N/C value obtained is well bellow the 1.33 expected for theoretical C 3 N 4 [3,5]. The saturation trend represents one of the major difficulties for obtaining carbon nitride films.…”

“…As a result of the nitrogen incorporation into carbon films it was found that both optical and the electrical properties [2,3], as well as the mechanical properties of the material can be modified. The mechanical properties are mainly controlled by the fraction of sp 3 bonded carbon, forming the skeleton of the material, the optical and electrical properties are determined by clustering of the sp 2 sites (rings or chains) and by the hydrogen content which decreases the connectivity of the sp 3 , forming termination CH n groups, therefore lowering the hardness of the material [4,5]. Conventional plasma deposition processes result in films where, both the H content and the sp 3 fraction decrease with increasing ion energy, so that films are polymer-like at low ion energy and graphite-like at high ion energy.…”

Effect of N2/CH4 flow ratio on microstructure and composition of hydrogenated carbon nitride films prepared by a dual DC-RF plasma system

“…The strong increase of N/C at a low content of N 2 in the gas mixture seems to be mainly due to the incorporation of nitrogen species coming from the plasma on the film surface during deposition [26]. Similar results have been reported for material grown in FCVA system [27] and Electron Cyclotron Wave Resonance [28]. The increase of the nitrogen content led to a sudden loss of sp 3 bonding, and consequent formation of fine graphite sp 2 bonded structures embedded in sp 3 matrix, which is to be further discussed later in the XPS analysis of the a-CN:H films.…”

“…The assignments of above binding energies are well established [30][31][32][33]. Additional peaks at the binding energies of 286.5 eV and 287.9 eV are related to nitrogen incorporation [28] and oxygen contamination, respectively. The binding energy values for the sp 2 and sp 3 components in the XPS C1s spectra of the a-CN:H films are consistent with that of the graphite and diamond mentioned above.…”