Y. Gerbig

Structure and mechanical properties of argon assisted carbon nitride films

Abstract This paper reports on the effects of Ar dilution on the structure, bonding and tribological properties of nitrogen-doped amorphous carbon films (a-C:H:N) deposited by r.f. glow discharge from CH 4 –N 2 and CH 4 –N 2 –Ar mixtures on silicon substrates. For different N 2 fractions, film structure and chemical composition were examined using Raman spectroscopy, X-ray reflectivity (XRR) and X-ray photoelectron spectroscopy (XPS). The mechanical and tribological properties were investigated by scratch testing and a tribometer in a ball-on-disk configuration. Results indicate that, as argon is introduced in the gas mixture, progressive graphitization of the films occurs and the mass density decreases. The behavior of the adhesive strength, as a function of nitrogen content, achieved with Ar addition is of the same order as those reported for CN x films. However, at a fixed nitrogen partial pressure, films obtained without Ar dilution show better adhesion and a denser sp 3 bonded carbon network.

Fluorinated amorphous carbon thin films: Analysis of the role of the plasma excitation mode on the structural and mechanical properties

The effects of pulsed plasma enhanced chemical vapor deposition on the thermally induced gas effusion characteristics of fluorinated amorphous carbon thin films are investigated. The main contributions to the effusion spectra are found to come from hydrogen, hydrocarbons, and CF4. With a plasma excitation frequency of 10−3 s, the film produced is relatively compact and the effusion of hydrogen-related species dominate. A strong change in the effusion characteristics for the highest on-time plasma excitation (10−1 s) indicates that an interconnected network of voids is present. Strong effusion of CF4 related species is in fact found to be consistent with a surface desorption process and can only be observed when the void network dimensions are large enough. Nanoindentation measurements showed increased elasticity of the film, as well as increased hardness upon reduction of the plasma excitation period. Raman spectroscopy was applied to corroborate the effusion results, indicating a structural transition fr...

Wear resistance of a high-nitrogen austenitic stainless steel coated with nitrogenated amorphous carbon films

In this paper, the dependence of wear resistance on grain size of nitrogen-alloyed austenitic stainless steel is investigated and compared to measurements for the same samples coated with nitrogenated amorphous carbon [a-C:H(N)] film, deposited by means of plasma-enhanced chemical vapour deposition. To this aim, ball-on-disk (BoD) tests were performed to investigate the wear stability of coated and uncoated substrates. Long-time test results on the uncoated material show that no improvement in the low-friction performance (LFP) duration was found with decreasing grain size of the substrate. On the other hand, an improvement in the low-friction performance duration with substrate microstructure refinement was found in the case of nitrogen-doped overcoats. An effect of the film structure on the LFP duration was also detected in the case of the finest-grained samples, indicating a synergic effect between the ultrafine grain structure and the nitrogen-doped carbon coating.

Spectroscopic analysis of the structure of amorphous nitrogenated carbon films after wear tests

Abstract The effects of wear tests on the electronic structure of amorphous nitrogenated carbon (a-C:H:N) films prepared in a radiofrequency plasma-enhanced chemical vapor deposition system from a mixture of methane and nitrogen have been investigated. The tribological properties were investigated with a tribometer in a ball-on-disk configuration. For different N 2 fractions, film structure and chemical composition were examined using conventional Raman and X-ray photoelectron spectroscopy, and also by means of high-lateral-resolution soft X-ray photoemission microscopy using synchrotron radiation. Nitrogen incorporation into the as-deposited amorphous carbon network results in an increase in the number of Nsp 2 -C bonded sites with respect to the films grown in a nitrogen-free atmosphere. The wear stability of the films was analyzed as a function of the nitrogen fraction, and a thorough description of the electronic structure was obtained in the as-deposited state and after wear testing. High-lateral-resolution photoemission microscopy reveals for the first time that inhomogeneities within the film after wear testing are correlated to nitrogen incorporation. The study of energy distribution curves and high-lateral-resolution images on the nitrogenated samples shows that a modification of the surface chemistry occurs by mechanical action.

Wear resistance of a high nitrogen austenitic stainless steel coated with amorphous carbon films: influence of grain size and film composition

In this paper, the wear resistance of nitrogen alloyed austenitic stainless steels is, for the first time, investigated and compared to that measured for the same samples coated with amorphous carbon (a-C:H) films deposited by means of plasma enhanced chemical vapour deposition. Ball on Disk (BoD) tests are performed in order to investigate the wear stability of coated and uncoated substrates with different grain sizes. For the uncoated samples, the BoD results show a strong dependence of the wear track volume versus grain size. Furthermore, a strong improvement of the wear resistance is found in a-C:H coated specimens with respect to the uncoated ones with the same substrate microstructure. The effects of nitrogen incorporation into the films are also investigated showing an improvement of the tribological properties of the coated stainless steel. In particular, a synergic effect is detected between the grain refining and the film in the case of nitride amorphous carbon overcoats with a consequent increase of the wear resistance.