Fullerene-like Hydrogenated Carbon Films Research Articles

Superlubricity of carbon nanostructural films enhanced by graphene nanoscrolls

Recently, macroscopic superlubricity has been realized by forming spherical geometries at a sliding interface to cause nanoscopic point contact. Here, we showed macroscopic superlubricity (~0.005) enhanced by graphene nanoscrolls, which were formed at the sliding interface of a tribological pair composed of graphite-like and fullerene-like hydrogenated carbon films.

Heating induced nanostructure and superlubricity evolution of fullerene-like hydrogenated carbon films

Fullerene-like hydrogenated carbon (FL-C:H) films hold superlubricity properties at room condition, which important for saving energy, for engine use, however, high temperature serving (below 500 °C) are needed considering. In this paper, FL-C:H films were annealed with protecting of nitrogen. The tribological test show that all films have superlubricity properties, of which friction coefficient are 0.008 (200 °C), 0.005 (250 °C), 0.004 (300 °C), 0.005 (400 °C), 0.004 (500 °C), respectively. In addition, the hardness is incremental when the annealed temperature increased from 200 to 300 °C, and decremental from 300 °C to 500 °C. Interestingly, the changes of hydrogen content can be neglect in present work. Combined HRTEM, Raman spectra and XPS results, one can speculate that the degree of order for FL-C:H films increase along with the argument of annealed temperature, but competition of growth and ordering of short-chain hydrocarbon and graphene stacks that determine the hardness and H3/E2 ratio, which further influences the wear volumes. However, the friction coefficient only depends on curved grahene which can formation scroll graphene between contact surface to low friction force.

Microstructure changes of self-mated fullerene-like hydrogenated carbon films from low friction to super-low friction with the increasing normal load

Self-mated fullerene-like hydrogenated carbon films (FL-C:H films) realized the conversion from low friction (~0.012) to super-low friction (~0.006) state due to the increasing normal load.The structure changes in the conversion and the effect of environments (N2 and humid air) on the structure changes were discussed by the combination of SEM, TEM, Raman and XPS spectra. With the increasing normal load, smaller wear scar area (or contact area) and thicker tribofilm could be observed. At smaller scale (such as nanoscale), not only more perfect graphitic structure can be formed, but newly formed longer graphitic sheets also tended to curve.

Synthesis of fullerene-like hydrogenated carbon films containing iron nanoparticles

Fullerene-like hydrogenated carbon films deposited by plasma enhanced chemical vapor deposition (PECVD) as compared with other methods can attain super-low friction and wear. But they often have bad adhesion to steel substrate and their structures are tailored by non-metal elements as F, N etc. In this work, we have prepared the films on steel balls by the combination of PECVD and plasma nitriding, among which iron nitride particles are sputtered and introduced in the films. The films have longer wear life and better adhesion to the steel substrate due to the N diffusion from iron nitride particles to the atom matrix of the ball.

Observation of structure transition as a function of temperature in depositing hydrogenated sp2-rich carbon films

In this study, we carried out the transition experiments of graphite-like (GL) to fullerene-like (FL) structures by placing high temperature steel substrates in the depositing environment which can form FL hydrogenated carbon films. We investigated the changes of bond mixtures, H content, aromatic clusters and internal stress at the transition process, and proposed the transformation mechanism inferred from Raman, TEM cross-section, FTIR and XPS results. It was found that the size of aromatic clusters and accordingly graphene planes and the formation of edge dangling bonds were the key steps. H+ bombardment leaded to the splitting of large graphene planes (at GL stage) into more and smaller planes (at FL stage) and the formation of edge dangling bonds; Some of these dangling bonds were reduced by the formation of pentagons and subsequent curving of the smaller planes, which were an indicator of FL structures.

The correlation between nano-hardness and elasticity and fullerene-like clusters in hydrogenated amorphous carbon films

Fullerene-like hydrogenated carbon films have outstanding mechanical and frictional properties, but their structures have never enjoyed elaboration. In this study, we investigate the relation between nano-hardness and elasticity and fullerene-like clusters by changing energy supply form (direct current and pulse) and H2 concentration in the feedstock. It is found that the films have a network of H-rich amorphous carbon and H-poor or -deficient fullerene-like carbon, and the network change can affect hardness and elastic recovery. This is due to the energy minimization process of the film growing system in a very short pulse period at low temperature.

Ultra-low friction and excellent elastic recovery of fullerene-like hydrogenated carbon film based on multilayer design

Multilayer fullerene-like hydrogenated carbon (FL-C:H) films were synthesized by using the chemical vapour deposition technique with a different flow rate of methane. The typical fullerene-like structure of as-prepared films was investigated by using transmission electron microscopy and Raman spectra. The prepared multilayered FL-C:H films showed a high elastic recovery ( $${\sim }$$ 90 $$\%$$ ), ultra-low friction coefficient ( $${\sim }$$ 0.019) and low wear rate $$({\sim }3.0\times 10^{-9}\,\hbox {mm}^{3}\,\hbox {Nm}^{-1})$$ in humid air.

Probing the effect of doped F and N on the structures and properties of fullerene-like hydrogenated carbon films

Richer fullerene-like (FL) structure interface layers with sp2‑carbon rich are observed in the sliding contacts of ultra-low friction fullerene-like hydrogenated carbon (FL-C:H) films, which can offer a new design possibility to further optimize these films' tribological performances by element doping such as hydrogen, fluorine and nitrogen. In this paper, we provide an understanding about the structure-performance relationship such as the effects of FL structures and incorporated elements such as fluorine and nitrogen. Meanwhile, the detailed structure, mechanical and frictional behaviors and surface properties of the doped films have been investigated. The results indicate that N atoms promote the formation of more cross-linked FL structure, while F atoms terminate sp2 bond linking state of curved graphitic similar to hydrogen, and thus destroy the FL continuous network structure. Moreover, the N-6 FL-C:H film exhibits higher hardness (~18.6GPa), better elasticity recovery (~83%) and a very smooth morphology (rms~0.242nm), lower friction (0.017) and wear (1.25×10−9mm3/Nm).

The tribological behaviors between fullerene-like hydrogenated carbon films produced on Si substrates, steel and Si3N4 balls

Fullerene-like hydrogenated carbon (FL-C:H) films were prepared on Si substrates, steel and Si3N4 balls by plasma enhanced chemical vapor deposition with methane gas. The frictional behaviors of steel/FL-C:H, Si3N4/FL-C:H, F-steel/FL-C:H and F-Si3N4/FL-C:H couples were investigated and their worn surfaces were analyzed by scanning electron microscopy (SEM) and 3D surface profiles. The results showed that the F-steel/FL-C:H and F-Si3N4/FL-C:H couples had lower friction and wear than the steel/FL-C:H and Si3N4/FL-C:H ones, respectively. The tribological differences are due to the change of microstructures and accordingly mechanical properties for FL-C:H films on a Si substrate, steel and Si3N4 balls.

Mechanical properties and tribological behavior of fullerene-like hydrogenated carbon films prepared by changing the flow rates of argon gas

Fullerene-like hydrogenated carbon (FL-C:H) films as carbon materials were prepared by direct current plasma enhanced chemical vapor deposition (dc-PECVD) technique. The content of FL nanostructure was confirmed by high-resolution transmission electron microscopy (HRTEM), visible Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). The effect of fullerene-like nanostructure on the friction behavior of the films was studied using a reciprocating ball-on-flat tribometer in humid environment. It is concluded that the curved FL nanostructure provide the film excellent mechanical properties and friction performance. Interestingly, combining with the results of Raman analyses of the wear debris, we find that new FL nanostructure form during the friction process. These new FL nanostructure may originate from the rapid annealing and stress relaxation of unstable carbon clusters.

Medium ion energy synthesis of hard elastic fullerene-like hydrogenated carbon film with ultra-low friction and wear in humid air

In this article, we prepared the fullerene-like hydrogenated carbon film by using the chemical vapor deposition (CVD) technique with pure CH4 and low ion energy supply (500V). The film exhibits high hardness (~16.8GPa), good elasticity recovery (~82%) and ultra-low friction (~0.023) and wear in humid air. Meanwhile, compared with previous deposition methods, this synthesis method offers advantages such as simpler operation, easier controlling, and lower cost.

Tribological study of hydrogenated amorphous carbon films with tailored microstructure and composition produced by bias-enhanced plasma chemical vapour deposition

We investigated the mechanical and tribological properties of hydrogenated amorphous carbon (a-C:H) films on silicon substrates by nanoindentation, ball-on-disc tribotesting and scratch testing. The a-C:H films were deposited from an argon/methane gas mixture by bias-enhanced electron cyclotron resonance chemical vapour deposition (ECR-CVD). We found that substrate biasing directly influences the hardness, friction and wear resistance of the a-C:H films. An abrupt change in these properties is observed at a substrate bias of about −100 V, which is attributed to the bias-controlled transition from polymer- to fullerenelike carbon coatings. Friction coefficients in the range of 0.28–0.39 and wear rates of about 7 × 10 − 5 mm 3/Nm are derived for the polymeric films when tested against WC–Co balls at atmospheric test conditions. On the other hand, the fullerenelike hydrogenated carbon films produced at ion energies > 100 eV display a nanohardness of about 17 GPa, a strong reduction in the friction coefficient (∼ 0.10) and a severe increase in the wear resistance (∼ 1 × 10 − 7 mm 3/Nm). For these films, relative humidity has a detrimental effect on friction but no correlation with the wear rate was found.

Fullerene-like hydrogenated carbon films with super-low friction and wear, and low sensitivity to environment

A novel hydrogenated carbon film containing fullerene-like nanostructure was prepared by pulse bias-assisted plasma enhanced chemical vapour deposition, and the fullerene-like arrangement in the film was characterized by high resolution transmission electron microscopy. The as-prepared hydrogenated carbon film exhibited super-low friction and wear in both dry N2 and humid ambient atmospheres, and was superior to the conventional hydrogenated carbon films. These excellent tribological properties could be attributed to the unique fullerene-like nanostructure, which endows the film with some special chemical and physical features, such as high chemical inertness, hardness and elastic recovery owing to the closed, curved and caged graphite planes, and hence, improves the tribological properties of the hydrogenated carbon film.

Effects of pulse bias duty cycle on fullerenelike nanostructure and mechanical properties of hydrogenated carbon films prepared by plasma enhanced chemical vapor deposition method

Fullerenelike hydrogenated carbon films were produced by pulse bias-assisted rf inductively coupled plasma enhanced chemical vapor deposition (ICPECVD). The effects of pulse duty cycle on the microstructure and mechanical properties of the resultant films were investigated by means of high resolution transmission electron microscopy (HRTEM), Raman spectroscopy, nanoindentation, and stress measurement. The low pulse duty cycle was found the key in the formation of fullerenelike structure in hydrogenated carbon films, and thus increased the hardness, elasticity, and internal stress of the films. The role of pulse duty cycle in evolution of fullerenelike structure was also discussed in terms of ion bombardment, hydrogen removal, and “annealing” effects.

The evolution of the structure and mechanical properties of fullerenelike hydrogenated amorphous carbon films upon annealing

Hydrogenated amorphous carbon films were deposited on Si (100) substrates using dc-pulse plasma chemical vapor deposition. Structurally, the as-deposited carbon films could be considered as nanocomposite thin films with fullerenelike microstructure in diamondlike carbon matrix based on our previous result [Q. Wang et al., Appl. Phys. Lett. 91, 141902 (2007)]. In this paper, the evolution of the structure and the mechanical properties of hydrogenated carbon films with fullerenelike microstructure on the annealing in vacuum was investigated. The fullerenelike hydrogenated carbon films annealed at 500 °C showed higher hardness (16.9% harder) and higher elastic recovery (11.2% higher) than the as-deposited films. The friction coefficient of fullerenelike hydrogenated carbon films in air with 40% relative humidity remained constant at about 0.037 when annealed at 600 °C. The wear rate of the films decreased sharply when annealed at 200 or 300 °C. Structural analysis shows that annealing at 300 °C improved tribological properties originated from the volume increase in the fullerenelike microstructure, and further annealing at 600 °C improved mechanical properties originated from the transformation of nanosized curved sp2 to sp3 clusters.

Super-low friction and super-elastic hydrogenated carbon films originated from a uniquefullerene-like nanostructure

Hydrogenated carbon films were grown by a plasma-enhanced chemical vapor deposition (PECVD) techniqueusing CH4 and H2 as feedstock at ambient temperature. The microstructure of the films was characterized byhigh resolution transmission electron microscopy (HRTEM). The images showed thepresence of curved basal planes in fullerene-like arrangements. An apparent amorphousgraphene structure with nm-sized packages of basal planes in a turbostratic feature wasobserved. The fabricated fullerene-like hydrogenated carbon films (FL–C:H) possesssuperior mechanical properties, i.e. high hardness (19 GPa) and high elasticity(elastic recovery of 85%). More importantly, the films exhibit ultra-low friction(μ = 0.009) under ambient conditions with 20% relative humidity.

Direct spectroscopic evidence of self-formed C60 inclusions in fullerenelike hydrogenated carbon films

The detection of self-formed C60 inclusions in hydrogenated carbon (C:H) with fullerenelike (FL) structure is reported. This material is synthesized by bias-enhanced electron cyclotron resonance chemical vapor deposition at low substrate temperatures (<120°C). The FL structure is identified by high-resolution transmission electron microscopy whereas the presence of C60 inclusions is derived from spectral signatures in the C(1s) x-ray absorption near edge structure. The formation of FL-C:H takes place for negative bias voltages higher than 100V, in parallel with dehydrogenation and drastic improvement of the tribomechanical film properties.