Studies on structure and electronic properties of amorphous nitrogenated carbon films prepared in dual electron cyclotron resonance–radio frequency plasma from a mixture of methane and nitrogen are presently reported. These films are characterized by Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, x-ray photoemission spectroscopy (XPS), ultraviolet photoemission spectroscopy (UPS), electrical conductivity measurement, and optical absorption spectroscopy. Symmetry breaking of aromatic rings are at a very small amount of nitrogen incorporation is understood from FTIR spectra. The relative contribution of C=N and C–N bonds is found to change with the variation of the nitrogen content in the samples, which shows a similar trend with the shift of the G peak to a higher wave number and the increase of the ID/IG ratio. From decomposition of XPS C 1s and N 1s peaks a three-phase model of CN bonds is proposed. UPS valence band spectra obtained by using a Helium II source, are decomposed into p-π, p-σ, 2s bands and a mixture of s-p band. The intensity of p-π band increases as a function of nitrogen concentration, confirming the increase of sp2 bonds in the samples. An enhancement of the room temperature electrical conductivity and a decrease of the optical gap are observed with the addition of nitrogen in the films. The effect of nitrogen doping in carbon films is also emphasized. Our analyses establish an interrelationship between the microstructure and electronic structure of nitrogenated carbon films, which helps to understand the change in electronic properties of the carbon films due to a low amount of nitrogen incorporation.
A surface model was developed for diamondlike-carbon film deposition, and was connected in a self-consistent way with a one-dimensional plasma chemistry and physics model for a CH4 radio-frequency (rf) discharge. The surface model considers the adsorption of multiple species (CH3, CH2, and H), and solves for the surface coverage of each species. Comparison is also done with a one-adsorbed-species model. Deposition is assumed to take place via direct ion incorporation, and ion-induced stitching of adsorbed neutrals; film removal takes place via etching and sputtering. The effects of ion flux/energy and surface temperature are examined in detail: At high ion energies direct ion incorporation dominates, in spite of competition with sputtering; at intermediate energies stitching prevails, while for lower ion energies etching can become largest. Mass balances are written at the surface–gas interface, permitting the determination of the effective sticking coefficients of the reacting neutrals. The sticking coefficients calculated from the surface model are fed back into the gas-phase chemistry model to recalculate the neutral densities. The process is repeated until a self-consistent solution is obtained. It is shown that the effective sticking coefficient of a neutral changes drastically from a low value for the plasma-off (or low ion energy) state, to a high value for the plasma-on and high ion energy state, resulting in higher consumption at the surface. The results show that it is imperative for meaningful results to solve surface and gas-phase chemistry models in a self-consistent way, a fact demonstrated by successful comparison with experimental data for the deposition rate and the gas-phase densities.
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