Huiwen Liu

Characterization of hydrogenated diamond-like carbon films electrochemically deposited on a silicon substrate

Diamond-like carbon (DLC) films were deposited on a Si substrate by electrolysis in a methanol solution at ambient pressure and low temperature. The morphology and microstructure of the resulting DLC films were analysed using atomic force microscopy, Raman spectroscopy, Fourier transformation infrared spectrometry, x-ray photoelectron spectroscopy (XPS), and x-ray excited Auger electron spectroscopy (XAES). The surface energy and mechanical properties of the DLC films were examined, and the growth mechanism of the DLC films in liquid phase electro-deposition is discussed as well. The results of the study show that the hydrogenated diamond-like carbon films are smooth and compact. The percentage of sp3 carbon in the DLC films is determined as 55?60%, based on the corresponding XPS and first-derivative XAES spectra of graphite, diamond, and the tested films. The DLC films show low surface free energy, good mechanical properties, excellent friction?reduction and wear-resistance. It is suggested that methanol dissociates to generate the active species of and C2H4 at high voltage applied to the electrode, followed by the generation of the alkyl chain [?CH2?CH2?]n whose C?C and C?H bond lengths and C?C?C and H?C?H bond angles are close to that of diamond. Subsequently, a diamond-like structure was formed by the ordered dehydrogenation of a short-chain [?CH2?CH2?]n in the electrolysis process.

Preparation and characterization of electrochemically deposited carbon nitride films on silicon substrate

Carbon nitride films (CNx films) were deposited on Si(100) substrates by the electrolysis of methanol–urea solution at high voltage, atmospheric pressure, and low temperature. The microstructure and morphology of the resulting CNx films were analysed by means of Raman spectroscopy, x-ray photoelectron spectroscopy (XPS), Fourier-transform infrared spectrometry (FTIR), x-ray diffraction (XRD), and atomic force microscopy. The tribological properties of the CNx films were examined on an UMT-2MT friction and wear test rig. The Raman spectrum showed two characteristic bands: a graphite G band and a disordered D band of carbon, which suggested the presence of an amorphous carbon matrix. XPS and FTIR measurements suggested the existence of both single and double carbon-nitride bonds in the film and the hydrogenation of the carbon nitride phase. The XRD spectrum showed various peaks of different d values, which could confirm the existence of the polycrystalline carbon nitride phase. The hydrogenated CNx films were compact and uniform, with a root mean square roughness of about 18 nm. The films showed excellent friction-reduction and wear-resistance, with the friction coefficient in the stable phase being about 0.08. In addition, the growth mechanism of the CNx films in liquid phase electro-deposition was discussed as well. It was assumed that the molecules of CH3OH and CO(NH2)2 were polarized under high electric field, and the CNx film was formed on the substrate through the reaction of the –CH3 and –NH2 groups on the cathode.

Preparation and characterization of hydrogenated diamond-like carbon films in a dual DC-RF plasma system

A dual direct current and radio frequency (DC-RF) plasma system was used to deposit hydrogenated diamond-like carbon (DLC) films from methane plasma. It has the advantages of separately controlling ion density and ion energy by RF power and DC bias, respectively, over conventional simply capacitive-coupled radio frequency plasma enhanced chemical vapour deposition system. Thus, the hydrogenated DLC films were obtained at different RF powers and DC biases, using CH4 plus Ar as the feedstock. The effects of RF power and DC bias on the structure and properties of the films were investigated by means of Fourier transformation infrared spectroscopy, Raman spectroscopy, x-ray photoelectron spectroscopy, and nano-indentation. The results were as follows: the sp3 content, hardness, and Youngs modulus of the DLC films increased with increasing RF power at a constant DC bias of ?200?V and reached the maximum values at an RF power of 300?W, after which they decreased with further increase of the RF power. The DC bias had a similar but greater effect on the structure and properties of the films, owing to a greater influence of the ion energy on the characteristics of the films than the ion current density. The film deposited at an RF power of 300?W and DC bias of ?200?V has the most diamond-like characteristics with maximum hardness, Youngs modulus, and sp3 content. Since both the ion current density and ion energy greatly affect the structure and characteristics of the DLC films, it is imperative to select proper processing parameters to obtain high quality DLC films.

Graded composition and structure in nanocrystalline Ni?Co alloys for decreasing internal stress and improving tribological properties

In this paper, nanocrystalline Ni?Co alloys with continuously graded composition and structure were produced by the electrodeposition method. The internal stress of the graded Ni?Co nanocrystalline alloys generated during the electrocrystallization and the tribological properties were investigated and compared with Ni?Co alloys with a uniform structure. The results show that with continuous changes in composition and structure, the internal stress generated during the electrodeposition process was decreased to approximately the minimum level. Additionally, the graded Ni?Co nanocrystalline alloys exhibited a remarkably improved wear resistance and a much lower friction coefficient compared with the Ni?Co alloys with a uniform structure under the dry sliding wear conditions. And the graded Ni?Co nanocrystalline alloys retain perfect friction and wear properties as the annealing temperature increases up to 400?C.

Effect of relative humidity on the tribological properties of hydrogenated diamond-like carbon films in a nitrogen environment

Hydrogenated diamond-like carbon (DLC) films were deposited on Si (100) wafers by a plasma enhanced chemical vapour deposition technique using CH4 plus Ar as the feedstock. The friction and wear properties of the resulting films under different relative humidities, ranging from 5% to 100%, in a nitrogen environment, were measured using a ball-on-disc tribometer, with Si3N4 balls as the counterparts. The friction surfaces of the films and Si3N4 balls were observed on a scanning electron microscope, and investigated by x-ray photoelectron spectroscopy. The results showed that the friction coefficient increased continuously from 0.025 to 0.09 with increase in relative humidity from 5% to 100%, while the wear rate of the films sharply decreased and reached a minimum at a relative humidity of 40%, then it increased with further increase of the relative humidity. The interruption of the transferred carbon-rich layer on the Si3N4 ball, and the friction-induced oxidation of the films at higher relative humidity were proposed as the main reasons for the increase in the friction coefficient. Moreover, the oxidation and hydrolysis of the Si3N4 ball at higher relative humidity, leading to the formation of a tribochemical film, which mainly consists of silica gel, on the friction surface, are also thought to influence the friction and wear behaviour of the hydrogenated DLC films.

Self-assembled stripes on the anodic aluminum oxide by atomic force microscope observation

Non-polished aluminum sheets were anodized. The nanostructures were investigated in details using an atomic force microscope (AFM). The coexistence of self-assembled stripes and porous arrays on the Al surface was observed. The formation mechanism of the stripes is discussed based on the Brusselator model. We suggest that the self-assembled patterns on the Al surface strongly depend on the competition of the formation and the dissolution rate of alumina film during the reaction process. It is also found that this type of ordered structure can only form in certain conditions.

The effect of solid lubricants on the tribological behaviour of zirconia at high temperatures up to

The tribological properties of TZP ceramics under solid lubrication up to have been investigated in this paper. The use either of graphite or of can reduce the friction coefficient and rate of wearing of TZP/ sliding couples from 25 to . However, their lubricating characteristics can deteriorate due to the oxidation of these lubricants at excessively high temperatures. Using and Cu can reduce the rate of wearing of TZP ceramics, but they have no apparent influence on the friction coefficient. exhibits good lubricating properties above , which is due to its complete crystallization and orientation along the (002) plane.