Ultra-elastic recovery and low friction of amorphous carbon films produced by a dispersion of multilayer graphene

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Abstract

Hydrogenated carbon films with embedded multilayer graphene were prepared by magnetron sputtering a Ni target in methane. The films demonstrate ultra-elastic recovery (81%) and low friction coefficient (0.06), in contrast with films that did not contain graphene, whose elastic recovery and friction coefficient are 50% and 0.12, respectively. The excellent mechanical properties were attributed to the presence of multilayer-graphene embedded in amorphous carbon matrix.

Graphical abstract

Highlights

► Target poisoning methods can be employed to grow carbon nanostructured films. ► Multilayer graphene will enhance the mechanical properties of amorphous carbon films. ► Multilayer graphene can improve the tribology properties.

Introduction

The mechanical and tribological behaviors of carbon films are not only related to bonding configuration, but also dominated to some extent by microstructure. Our recent work has shown that the introduction of carbon allotropes, such as fullerene, nanotube and expanded graphite, could decrease the internal stress and increase the hardness and elasticity of amorphous carbon films [1], [2], [3]. The presence of fullerene-like structure brought ultra high elasticity and super low friction to amorphous carbon films [4], [5].

Graphene is the two-dimensional building block for carbon allotropes of every other dimensionality. It was predicted to have a range of unusual properties, such as electronic properties, thermal conductivity, mechanical stiffness and high elasticity [6]. If graphenes are introduced into carbon films, we deduce that the graphene contained amorphous carbon films may possess interesting properties. It was verified in our previous work that the incorporation of multilayer graphene oxide sheets into amorphous carbon films by liquid process showed an improved hardness and elastic recovery [3]. However, amorphous carbon and graphene are normally grown by different methods, so the growth of graphene contained amorphous carbon structures by chemical or physical vapor deposition is a challenge. Encouragingly, it is well known that, noble metals (Ru, Pt and Ni) were extensively used as catalysts for the deposition of graphene layers [7], [8]. In the present work, graphene-like structures were intentionally grown on the Ni target surface firstly and then sputtered off to deposit onto Si substrate to form graphene embedded amorphous carbon films. The graphene embedded amorphous carbon films showed both ultra-elastic recovery (81%) and low friction coefficient (0.06).

Section snippets

Film deposition

Prior to the deposition, a base pressure of 4.0 × 10 3 Pa was attained. Then methane (99.99%) was introduced into the chamber as the plasma source and the reactive gas. The gas pressure was kept at 0.4 Pa during the whole experimental process. In the first step, the substrate holder backed against the Ni target. A layer of carbon film (Fig. 1) was grown firstly on the Ni (99.6%) target surface to prevent Ni from being sputtered out (by sputtering Ni target in methane for 5 min, with sputtering power

Composition and structure analyses of the films

The plane and cross-section FESEM images of the carbon films grown on Ni target (Fig. 1) show a porous structure. The inserted Raman spectrum (Fig. 1a) with two sharp peaks implies that the grown film is highly ordered [10]. Two second-order Raman peaks centered at 2700 and 3200 cm 1, corresponding to the 2D and 2 G vibration, also appear, indicating the presence of ordered structures [11]. The HRTEM image (Fig. 1b) indicates that the films grown on target surface are layered structure [12].

The

Conclusions

In conclusion, the graphene/amorphous carbon composite films can be prepared by magnetron sputtering Ni target in methane. The multilayer graphene structure was generated from the decomposition of methane on Ni target which is usually used as catalyst to fabricate graphene, and then the multilayer graphene were sputtered out and grew up into carbon matrix on Si substrate due to the annealing effect of plasma. This unique structure of the films restrains plastic deformation, which in turn

Acknowledgments

The project was supported by “863” program (No. 2007AA03Z338) of the Ministry of Science and Technology of China and National Natural Science Foundation of China (Nos. 50823008, 50975273).

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