Elsevier

Surface and Coatings Technology

Volume 206, Issue 5, 25 November 2011, Pages 1007-1010
Surface and Coatings Technology

Effect of hydrogen flow on the properties of hydrogenated amorphous carbon films fabricated by electron cyclotron resonance plasma enhanced chemical vapor deposition

https://doi.org/10.1016/j.surfcoat.2011.03.107Get rights and content

Abstract

The hydrogenated amorphous carbon films (a-C:H, so-called diamond-like carbon, DLC) have exceptional physical and mechanical properties and have wide applications. In the present study, amorphous hydrogenated carbon films (a-C:H) have been deposited on a Si (100) substrate at different hydrogen flow using electron cyclotron resonance chemical vapor deposition (ECR-CVD). The flow of hydrogen changed from 10 sccm to 40 sccm and the flow of acetylene was fixed at 10 sccm. The microstructure and properties of the a-C:H were measured using visible Raman spectra, Fourier transform infrared (FTIR) spectroscopy, UV–VIS spectrometer,surface profilometer and nano-indentation. The results showed that the sp3 content and sp3–CH2 structure in the amorphous hydrogenated carbon films increased with the hydrogen flow. The deposition rate decreased with the hydrogen flow. The residual stress and the nano-hardness of the amorphous hydrogenated carbon films increased with the hydrogen flow. Consequently, the a-C:H film become more diamond-like with the increase of hydrogen flow.

Highlights

► The a-C:H films have been deposited at different hydrogen flow using ECR-PECVD. ► The sp3 content and sp3–CH2 structure increased with the hydrogen flow. ► The deposition rate decreased with the hydrogen flow. ► The residual stress and the nano-hardness increased with the hydrogen flow.

Introduction

Joint replacement surgery is most commonly applied on hips, knees, and shoulders. But the particles from the implanted joints caused by friction process lead to long-term loosing between the implant and the bone. Because of this, a wear-reducing coating on the metal component, which is also biocompatible, should dramatically extend hip implant life. Diamond-like carbon (DLC), with its extreme smoothness, hardness, low coefficient of friction and biocompatibility, is an excellent candidate for such an application [1]. Since the deposition of DLC was first reported by Aisenberg [2], numerous deposition techniques have been developed, such as sputtering deposition [3], cathodic arc deposition [4], pulsed laser deposition [5], plasma enhance chemical vapor deposition [6], etc. Among these techniques, ECR-PECVD (electron cyclotron resonance plasma enhanced chemical vapor deposition) method with pulse power has a number of features which make it an attractive method. For example, microwave ECR plasma creates a high ion density and electron temperature at low pressures. The hydrogenated amorphous carbon films (a-C:H) can be deposited from different source gases such as CH4, C2H2, C2H4, C6H6, which can provide the source of carbon atoms. In addition, auxiliary gases like argon or hydrogen are also necessary because they can etch the sp2 bonding and stabilize the sp3 bonding. In other words, the auxiliary gas (hydrogen) affects the structure of a-C:H film. The high proportion of auxiliary gas (H2) leads to high sp3 content and the hydrogen flow was controlled 10 times than hydrocarbon [7] in the deposition process. However, for an artificial joint coating, the films with high hardness are adverse to decrease the wear debris and particles from joint cup (made by polyethylene). In order to decrease the hardness of the a-C:H film, this paper focused on the condition that the hydrogen flow was 1–4 times to the acetylene.

The properties such as mechanical property, adhesion force and biocompatibility were determined by the structure of the a-C:H films which used on the artificial joint. This paper reports the effect of hydrogen flow on the structure, especially the sp3 content and the C–H related bond of a-C:H films deposited by ECR-PECVD.

Section snippets

Experimental procedure

The a-C:H films used in the present study had been deposited in the ECR-PECVD system shown schematically in Fig. 1 [8]. The system consists of a cylindrical vacuum chamber and a microwave plasma power to create plasma inside a 50 cm diameter quartz dome. The microwave was guided through a rectangular waveguide and introduced into the ECR magnetron excitation chamber through a quartz window. The top of the chamber was surrounded by a set of solenoids to provide the necessary magnetic field. The

Results and discussion

Fig. 2 showed the deposition rates of the a-C:H films deposited at different hydrogen flows. It showed that the deposition rates decrease with the increase of hydrogen flow. As a general rule, the deposition rates are determined by the balance between the deposition of hydrocarbon radicals and ions and the etching by ion bombardment [9]. With the increase of H2 gas flow, the H+ etching effect increases. At the same time, the content of carbon ion in plasma is reduced, the carbon ion flux onto

Conclusion

Diamond-like carbon films are successfully deposited using ECR-PECVD method. The influence of hydrogen gas flow on the property and structure of a-C:H films is investigated. The deposition rate decreases from 3.8 nm/min to 2.8 nm/min as the hydrogen flow increased from 10 sccm to 40 sccm. The Raman and UV–VIS results indicate that the sp3 content changes as a function of hydrogen flow. The sp3 carbon atom content increases with the hydrogen flow. FTIR spectra indicate that the sp3–CH2 structure

Acknowledgements

This work was supported by NSAF (#10876030), the Fundamental Research Funds for the Central Universities (SWJTU11CX125) and the National High Technology Research and Development Program of China (863 Program #2006AA02A135).

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