Carbon nitride (CNx) and amorphous carbon (a-C) thin films are deposited by reactive magnetron sputtering onto silicon (001) wafers under controlled conditions to achieve amorphous, graphitic and fullerene-like microstructures. As-deposited films are analyzed by Spectroscopic Ellipsometry in the UV–VIS–NIR and IR spectral ranges in order to get further insight into the bonding structure of the material. Additional characterization is performed by High Resolution Transmission Electron Microscopy, X-ray Photoelectron Spectroscopy, and Atomic Force Microscopy. Between eight and eleven resonances are observed and modeled in the ellipsometrically determined optical spectra of the films. The largest or the second largest resonance for all films is a feature associated with C–N or C–C modes. This feature is generally associated with sp3 C–N or sp³ C–C bonds, which for the nitrogen-containing films instead should be identified as a three-fold or two-fold sp² hybridization of N, either substituted in a graphite site or in a pyridine-like configuration, respectively. The π→πlow asterisk electronic transition associated with sp² C bonds in carbon films and with sp² N bonds (as N bonded in pyridine-like manner) in CN_x films is also present, but not as strong. Another feature present in all CN_x films is a resonance associated with nitrile often observed in carbon nitrides. Additional resonances are identified and discussed and moreover, several new, unidentified resonances are observed in the ellipsometric spectra.

This book highlights some of the most important structural, chemical, mechanical and tribological characteristics of DLC films. It is particularly dedicated to the fundamental tribological issues that impact the performance and durability of these coatings. The book provides reliable and up-to-date information on available industrial DLC coatings and includes clear definitions and descriptions of various DLC films and their properties.

In 1994, researchers at Linköping University discovered the fullerene-like allotrope of carbon nitride (FL-CN_x) by using reactive magnetron sputtering in a nitrogen-containing atmosphere at rather low ion energy assistance. FL-CN_x is a predominantly sp₂-hybridized material with nitrogen structurally incorporated either substitutionally in a graphite sheet or in a pyridine-like manner, which initiates bending by formation of pentagons and cross-linking, respectively. The assumed nitrogen-induced cross-linkage between the sheets contributes considerably to the strength of FL-CN_x by preventing interplanar slip. This results in an extremely fracture tough, elastic, and compliant material, which deforms by reversible bond rotation and bond angle deflection rather than slip and bond breaking.

Even though the synthesis of super-hard-crystalline ?- C3 N4 remains elusive, noncrystalline C Nx compounds are of increasing importance owing to their competitive properties. Especially the fullerene-like allotrope of C Nx exhibits outstanding elasticity in combination with low work of indentation. This new class of thin solid film materials is characterized by a microstructure of bent and intersecting basal planes. Substitutional incorporation of nitrogen into the predominantly s p2 hybridized graphitic layer triggers the formation of curvature-inducing pentagons and interplanar cross-links at a much lower energy cost as compared to carbon-only materials. The term "fullerene- like" was coined to reflect the nanometer scale of curved structural units. Thus, fullerene-like C Nx deforms by bond angle deflection and compression of the graphitic interplanar lattice spacing, whereas the superior strength of the s p2 bonds inhibits plastic deformation giving the material an extremely resilient character. The orientation, radius of curvature of basal planes, and density of cross-linking can be adjusted by the synthesis conditions. Here, the existence of significant numbers of precursor molecules is a determining factor. The inherent resiliency of the material in combination with the carbon-based beneficial friction promises to give rise to numerous tribological applications. © 2007 American Vacuum Society.

Nanocomposite Ti-Si-C thin films were deposited by dc magnetron sputtering from a Ti3SiC2 target onto Si(1 0 0) and high-speed steel substrates at 300 °C. The as-deposited films consisted of nanocrystalline (nc-) TiCx and amorphous (a-) SiCx, as determined by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Annealing in vacuum up to 1450 °C resulted in improved crystallinity and a decreased volume fraction of the amorphous phase. Additionally, differential scanning calorimetry (DSC) was used to monitor heat flows connected to the respective reactions in the material, where a broad exothermic peak attributed to grain growth of crystalline TiCx appeared, while an exothermic reaction related to the formation of Ti3SiC2 was not detected. Tribological testing in a ball-on-disk setup was conducted at room temperature, 500 and 700 °C against an alumina counterpart. The room temperature measurement resulted in a coefficient of friction value of 0.8, at elevated temperatures the coefficient of friction decreased to 0.4. © 2006 Elsevier B.V. All rights reserved.

Amorphous carbon nitride (CNx) coatings are now being developed for a range of applications, e.g. as a protective top layer for hard disks or as a coating to reduce the friction between synthetic joints in the human body. The purpose of this work is to assess the mechanical properties of the latest generation of fullerene-like CNx deposited on different substrates in order to expand the number of potential applications. Samples of CNx on four different substrates have been studied using quasistatic nanoindentation with a wide range of peak loads, from 500 mu N to 500 mN and dynamic nanoindentation for peak loads from 100 mu N to up to 10 mN. Improved deposition techniques generate samples with extremely high values of hardness/Young's modulus, in some cases greater than 0.4 which is not achieved by any other hard material. Adhesion and fracture resistance are comparable to or better than that of traditional high hardness coatings, such as SiC and TiN, on similar substrates. The sample of CNx on titanium showed differences in hardness and Young's modulus at low loads, where the influence of the substrate is negligible, compared to coatings deposited on other substrates. This arises due to the fact that Ti from the substrate may have diffused into the coating in the deposition process creating a sort of C-N-Ti high hardness layer which would have some advantages of both the fullerene-like and traditional hard coating systems. (c) 2005 Elsevier B.V. All rights reserved.

Carbon nitride (CN_x) thin films were deposited on silicon (100) and (111) substrates at 300 °C by laser ablation of a graphite target using a pulsed Nd:YAG laser in a nitrogen atmosphere. The composition and structural properties of the films were investigated as functions of gas pressure and laser fluence. X-ray photoelectron spectroscopy (XPS) revealed a strong dependence of the amount of structurally incorporated nitrogen upon gas pressure. A maximum was observed at the highest laser fluence of 10 J/cm² and at an intermediate pressure of 4 Pa. Further analyses of the XPS N 1s core level spectra of the CN_x films, exhibiting the highest elasticity in nanoindentation experiments, revealed a typical double-peak arrangement; most pronounced for the highest laser fluence at low pressures. These two peak components indicate that the nitrogen bonded onto a graphitic structure dominates over the two-fold coordinated pyridine-like bonding configuration. This favors the growth of intersecting corrugated graphene structures that may be considered to have “fullerene-like” microstructures. Additionally, Fourier Transformed Infrared Spectroscopy analyses of films deposited at different pressures show the presence of 2229 and 2273 cm^{− 1} stretching peaks associated with CN triple bonds (CN) of nitriles and isocyanides, 1640 cm^{− 1} and 1545 cm^{− 1} associated with the CC and CN and a peak at 1730 cm^{− 1}, which is connected to the CO carbonyls groups. Films grown at 0.66 Pa revealed the strongest CN peak.

Humidity influences the tribological performance of the head–disk interface in magnetic data storage devices. In this work we compare the uptake of water of amorphous hydrogenated carbon (a-CH_y) and carbon nitride (a-CN_x) films, widely used as protective overcoats in computer disk drive systems, with two types of amorphous non-hydrogenated carbon (a-C and a-C_sp²) films, and fullerene-like carbon nitride (FL-CN_x) films. Carbon films were deposited on quartz crystal substrates by reactive dc magnetron sputtering in Ar/N₂ discharges. After deposition, some of the films were coated with a 2-nm-thick layer of Z-tetraol, a lubricant used in hard disk devices. A quartz crystal microbalance placed in a vacuum chamber was used to measure the adsorption of water at room temperature and at pressures of water corresponding to relative humidities in the range RH = 0 to 90%. Water adsorption and desorption is fast, indicating that equilibrium with ambient humidity is reached on time scales of minutes, much faster than the time scales for fluctuations in ambient humidity. The amount of water adsorbed on the non-lubricated amorphous carbon films is significantly higher than that on the fullerene-like films. The presence of the lubricant influences water adsorption but its impact differs on different carbon films.

The bonding structure of highly ordered fullerenelike (FL) carbon nitride (CNx) thin films has been assessed by x-ray absorption near-edge spectroscopy (XANES). Samples with different degrees of FL character have been analyzed to discern spectral signatures related to the FL microstructure. The XANES spectra of FL-CNx films resemble that of graphitic CN x, evidencing the sp2 hybridization of both C and N atoms. The FL structure is achieved with the promotion of N in threefold positions over pyridinelike and cyanidelike bonding environments. In addition, the relative p* / σ* XANES intensity ratio at the C(1s) edge is independent of the FL character, while it decreases ∼40% at the N(1s) edge with the formation of FL arrangements. This result indicates that there is no appreciable introduction of C-sp3 hybrids with the development of FL structures and, additionally, that a different spatial localization of π electrons at C and N sites takes place in curved graphitic structures. The latter has implications for the elastic properties of graphene sheets and could, as such, explain the outstanding elastic properties of FL-CNx.