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In this letter we report the controlled growth and microstructural evolution of self-assembled nanocomposite multilayers that are induced by surface ion-impingement. The nanoscale structures together with chemical composition, especially at the growing front, have been investigated with high-resolution transmission electron microscopy. Concurrent ion impingement of growing films produces an amorphous capping layer 3 nm in thickness where spatially modulated phase separation is initiated. It is shown that the modulation of multilayers as controlled by the self-organization of nanocrystallites below the capping layer, can be tuned through the entire film.

The influence of oxygen concentration on the structure and mechanical properties of V0.5Al0.5OxN1−x thin films (0 ≤ x ≤ 0.8) was investigated. The unexpected experimental lattice parameter decrease with increasing oxygen concentration can be understood based on ab initio data: the oxygen incorporation induced formation of metal vacancies reduces the equilibrium volume and stabilizes the metastable solid solutions. Charge balancing is identified as the underlying physical mechanism by Bader decomposition analysis. Hence, property predictions for these oxynitrides are only meaningful if the defect structure is described.

Influence of surface roughness on the friction of TiC/a-C nanocomposite coatings while sliding against bearing steel balls in humid air was examined by detailed analyses of the wear surfaces and the wear scar on the ball counterparts by atomic force microscopy, optical, and confocal microscopy. It was observed that the surface roughness of the coatings essentially determines the wear behavior of the ball counterpart, which consequently influences the transfer film formation. A rough coating causes abrasive wear of the steel ball during the running-in period, which impedes the formation of a stable transfer film and leads to higher values of coefficient of friction (CoF). Moreover, the CoF does not show a decreasing trend after the running-in period, although the roughness of the coating was greatly reduced. Replacing the worn ball with a new one after the running-in period yields lower CoF values similar to that observed for a smooth coating. In both of the cases, no wear of the steel ball occurs and a stable transfer film forms and effectively covers the contact area. The influence of the wear debris on the formation of the transfer film is also discussed.Keywords Roughness Á Friction Á Hardness Á Nanocomposite coating For metals, in most cases, initial surface textures are rapidly destroyed as soon as wear starts. However, under low loading conditions and/or for materials with a high hardness, wear rate is low and thus the initial surface roughness may play an important role in tribology. This is usually the case of hard protective coatings . The low friction of these coatings has been mainly attributed to the formation of a transfer film on the sliding surfaces of the counterface materials. The transfer film is believed to be formed by a friction-induced phase transformation of surface layer of DLC [7], and is mainly composed of amorphous graphitelike carbon that isolates the counterface material. As a result, sliding occurs mainly between the transfer film and the DLC coating, yielding low friction [8]. The presence of small amount of metal from the coating and its oxides as well as the iron oxides (due to oxidation of iron from the steel ball counterpart) in the transfer film in the case of the metal containing DLC are reported [4,5,9]. Also the presence of metal carbide (TiC) nano-crystallites, at the sliding surfaces, enhances the surface graphitization of the DLC matrix and promote formation of transfer film [3]. The density and chemical nature of the transfer film largely influence the CoF. The transfer film formation is affected by the environment, contact pressure, and sliding velocity [10][11][12]. The surface roughness of DLC coatings may also influence the

Mechanical, structural, chemical bonding (sp 3 /sp 2), and tribological properties of films deposited by pulsed-DC sputtering of Ti targets in Ar/C 2 H 2 plasma were studied as a function of the substrate bias voltage, Ti-target current, C 2 H 2 flow rate and pulse frequency by nanoindentation, Raman spectroscopy and ball-on-disc tribometry. The new findings in this study comprise: dense, column-free, smooth, and ultra-low friction TiC/a-C:H films are obtained at a lower substrate bias voltage by pulsed-DC sputtering at 200 and 350 kHz frequency. The change in chemical and phase composition influences the tribological performance where the TiC/a-C:H films perform better than the pure a-C:H films. In the case of TiC/a-C:H nanocomposite films, a higher sp 2 content and the presence of TiC nanocrystallites at the sliding surface promote formation of a transfer layer and yield lower friction. In the case of a-C:H films, a higher sp 3 content and higher stress promote formation of hard wear debris during sliding, which cause abrasive wear of the ball counterpart and yield higher friction.

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An analysis of dynamic roughening and smoothening mechanisms of thin films grown with pulsed-dc magnetron sputtering is presented. The roughness evolution has been described by a linear stochastic equation, which contains the second-and fourth-order gradient terms. Dynamic smoothening of the growing interface is explained by ballistic effects resulting from impingements of ions to the growing thin film. These ballistic effects are sensitive to the flux and energy of impinging ions. The predictions of the model are compared with experimental data, and it is concluded that the thin film roughness can be further controlled by adjusting waveform, frequency, and width of dc pulses.