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Abstract Diamond-like carbon (DLC) films were deposited on the nitrile butadiene rubber substrates by magnetron sputtering. The effects of the Ar sputtering pressure (SP) on the surface topography, structure, wettability and tribological performance of the DLC films were investigated. The DLC films' morphology as a function of SP was studied by atomic force microscopy, and their structural properties were investigated using Raman spectroscopy and FTIR. The Raman results revealed that a high SP contribute to forming sp3 bonds. The surface energy was calculated by the Owens-Wendt-Rabel-Kaelble method, and it peaked at a SP of 1.4 Pa. Tribological tests were performed using a ball-on-disc tribometry at a fixed load of 0.3 N under ambient conditions, which revealed that the tribological characteristics of DLC films can be tuned by varying the SP. The results showed that the DLC films prepared under 1.4 Pa SP exhibited enhanced triboperformance, based on a stable coefficient of friction lower than 0.25 during the whole test, which was very promising for practical tribological applications. [ABSTRACT FROM AUTHOR]

Abstract: The threading dislocation density of hydride vapor phase epitaxy (HVPE)-grown thick GaN layers was measured by high-resolution X-ray diffraction (HR-XRD). Three models were compared, namely mosaic model, Kaganer model and modified Kaganer model. X-ray rocking curves (XRC) of (0002), (101¯5), (101¯4), (101¯3), (101¯2), (101¯1) and (101¯0) planes were recorded for quantitative analysis. The screw-, edge-, and mixed-type threading dislocation densities were simulated from the XRD line profile by using the three models. The dislocation density was also measured by atomic force microscopy (AFM), wet chemical etching and cathodoluminescence (CL). The results showed that the Kaganer model was more physically precise and well explained the rocking curve broadening for HVPE-grown high-quality GaN compared with the mosaic model. Assuming a randomly distributed threading dislocation configuration, we modified the Kaganer model. Based on the modified Kaganer model, the edge and screw threading dislocation densities in HVPE-grown GaN thick films ranging from 20μm up to 700μm were analyzed. It was shown that screw-type dislocation density decreased more rapidly than edge-type dislocation with increase in film thickness. [Copyright &y& Elsevier]

To promote the adhesion strength between diamond-like carbon (DLC) films and nitrile butadiene rubber (NBR) substrates, titanium-doped carbon (Ti-C) films prepared by dual-target magnetron sputtering under varied substrate bias voltages were used as an interlayer on the rough NBR. The surface topography and structure of Ti-C films were investigated by atomic force microscopy (AFM) and Raman spectra. Raman analysis indicates that the increase of substrate bias voltage leads to an increase of the number or the size of sp2 clusters in the Ti-C interlayer. The adhesion strength and tribological properties of DLC films coated on NBR substrate were scrutinized by a scratch tester and a ball-on-disk tribometer, respectively. It was found that DLC film with a Ti-C interlayer at a certain bias voltage exhibited superior wear resistance with a low coefficient of friction (CoF) during the sliding of 6000 laps. No clear damages in the coatings were observed from the wear tracks. Besides, the scratch test also revealed a reliable adhesion when the interlayer was prepared at −150 V, as confirmed by a scratch crack width of ~50 μm as compared to that of the pure DLC film increasing to ~ 120 μm. Therefore, a Ti-C interlayer could significantly enhance the adhesion and wear resistance of DLC thin films deposited on NBR. Unlabelled Image • A Ti-C interlayer on rubber promotes the adhesion of diamond-like carbon film. • The tribology property of diamond-like carbon film is tailored by the Ti-C interlayer. • The wear resistance of diamond-like carbon film on rubber is tuned by bias voltage. [ABSTRACT FROM AUTHOR]