Elsevier

Thin Solid Films

Volume 529, 1 February 2013, Pages 301-305
Thin Solid Films

Effect of feed gas composition effects on the nanotribological properties of diamond-like carbon films

https://doi.org/10.1016/j.tsf.2012.03.107Get rights and content

Abstract

A series of experimental nanoindentation, nanowear and nanoscratch tests was conducted to investigate the relationship between the nanotribological characteristics of diamond-like carbon (DLC) and feed gas composition used for the deposition. The DLC films were deposited on silicon substrates in radio-frequency plasma enhanced chemical vapor deposition system with a mixture of hydrogen and methane gases. Raman spectroscopy results show that the integrated intensity ratios (ID/IG) of each profile correlate with sp2/sp3 ratios. The result also indicates that the hydrogen content in the source gas has a significant influence upon the sp2/sp3 ratio and hydrogen-to-carbon ratio in DLC films. It is demonstrated that the sp2/sp3 ratio decreases with increasing hydrogen content in the DLC film. Our result also reveals that a significant relationship between the hydrogen content and the nanotribological characterizations of the DLC films, namely lower hydrogen-to-carbon ratio leads to higher hardness, elastic modulus, friction coefficient, and lower wear depth. The surface reinforcement can be attributed to the fact that variation of surface energy arises from the different carbon hybridized states (sp2/sp3 ratio), which improve the surface properties via the hydrogen content in the source gas and associated nanotribological characteristics.

Highlights

► Tribological diamond-like carbon (DLC) coatings were prepared. ► RF-plasma-enhanced chemical vapor deposition with H2 and CH4 gas mixture ► Integrated intensity ratios (ID/IG) have been correlated with sp2/sp3 ratios. ► Tribological properties of DLC films studied by nanoindentation

Introduction

For decades, diamond-like carbon (DLC) films have attracted a desirable interest from both industry and the scientific community. DLC is a unique coating material for hardening the surface of moving mechanical parts, especially for tribological applications. DLC coatings are attractive for tribological applications because of their favorable properties including low friction coefficient, high mechanical hardness and excellent chemical inertness. DLC coatings have been the subject of growing attention within tribological applications as a result of their high hardness, high wear resistance, low friction coefficient, excellent chemical inertness, and their potential for use in a variety of energy-saving applications. Previous studies show that preparation methods can result in different compositions and rations, hence affect the film properties (composition, carbon bonding, surface roughness, mechanical strength, tribological behavior and electrical resistivity) [1], [2], [3], [4], [5], [6], [7], [8], [9], [10]. In general, the sp3- and sp2-bonded carbons have been revealed to coexist in amorphous or crystalline carbon microstructures and nanostructures [11], [12], [13], [14], [15], [16], [17].

Fontaine et al. [17] studied the effect of the hydrogen contents on the friction coefficient of DLC films. Their results showed that the friction coefficient for lower hydrogenated DLC films rises up to 0.6. By contrast, in the case of DLC films with the higher hydrogen content, the friction decreases down to lower values (less than 0.01). Therefore, the hydrogen content of the DLC films and the nature of the carbon–hydrogen bonds are now widely recognized to play a paramount role on the friction coefficient observed. A similar performance has also been reported for the tribological behaviors of hydrogenated and hydrogen-free DLC coatings by Ronkainen et al. [18]. Recently, many research works have been published on tribological phenomena of DLC films using a pin-on-disk tester or ball-on-disk tribometer [19], [20], [21], [22]. However, such conventional tests based on continuum theory might break down when the physical dimension falls in the nanometer regime. Recent development of nanotechnology provides a unique opportunity to microscopically manipulate various nano-mechanisms to achieve desirable tribological performances and good interfacial behaviors. In this study, we have employed nanoindentation to characterize tribological properties of DLC thin films for which a depth-sensing technique also was utilized to determine mechanical properties through the analysis of the load-depth curve. These DLC films have been deposited on a silicon substrate using radio frequency plasma enhanced chemical vapor deposition (RF-PECVD) method with pure methane gas (CH4) or a mixture of H2 and CH4 gases as the source gas. The nanotribological and nanowear properties for the DLC films were investigated by the nanoscratch tests. The topography of the wear tracks of samples prepared using various H2 contents in the fed gas was examined by scanning probe microscopy (SPM). Moreover, the role of H2 content in the deposition process on the properties of DLC films was examined using Raman spectroscopy, which has proven to be a powerful method to characterize DLC films.

Section snippets

Experiments

In this present study, the DLC films were deposited on a silicon substrate using the capacitively-coupled radio frequency (RF) plasma enhanced chemical vapor deposition (RF-PECVD) method [23]. The substrates were mounted on the RF-powered electrode with a negative dc self-bias of 220–250 V. The electrode was cooled in flowing water to keep the substrate near room temperature during the deposition of DLC films, and the substrate temperature was measured using a K-type thermocouple. The substrate

Result and discussion

The Raman analyses are performed for various DLC films derived from pure methane and various hydrogenated methane gas discharge plasmas. The results, shown in Fig. 1, indicate that the film structure contains both G-band and D-band, in which the two peaks in the curves correspond to peaks for G-band and D-band, the former being centered at 1560 cm 1, the latter at 1350 cm 1. In general, the shift of G band to a lower wavenumber usually reflects the increase of sp3 bonds, in which the ID/IG ratio

Conclusions

In this present study, DLC films were deposited by RF-PECVD using a mixture of hydrogen and methane gases. Raman spectroscopy results show that the integrated intensity ratios (ID/IG) of each profile correlate with sp2/sp3 ratios. The present result also indicates that the sp2/sp3 ratio and hydrogen-to-carbon ratio in DLC films strongly depended on hydrogen content in the source gas. In addition, a series of experimental nanoindentation, nanowear and nanoscratch tests has been employed to

Acknowledgment

The authors gratefully acknowledge the support provided to this research by the National Science Council, Taiwan, NSC 100-2120-M-194-002 and NSC 100-2120-M-194-004. The support of AFOSR under Contract No. FA4869-06-1-0056 AOARD 114105 is also acknowledged.

References (41)

  • S. Neuville et al.

    Thin Solid Films

    (2007)
  • M. Jelinek et al.

    Mater. Sci. Eng. B

    (2010)
  • Q. Zeng et al.

    Thin Solid Films

    (2011)
  • D. Caschera et al.

    Thin Solid Films

    (2011)
  • D. Caschera et al.

    Thin Solid Films

    (2011)
  • W. Zhang et al.

    Thin Solid Films

    (2002)
  • M. Suzuki et al.

    Diamond Relat. Mater.

    (2003)
  • J. Fontaine et al.

    Surf. Coat. Technol.

    (2001)
  • H. Ronkainen et al.

    Wear

    (2001)
  • A. Erdemir

    Tribol. Int.

    (2004)
  • A. Erdemir et al.

    Diamond Relat. Mater.

    (2000)
  • A. Erdemir et al.

    Surf. Coat. Technol.

    (2000)
  • A. Erdemir

    Surf. Coat. Technol.

    (2001)
  • R. Saha et al.

    Acta Mater.

    (2002)
  • S.M. Han et al.

    Thin Solid Films

    (2011)
  • M. Weidner et al.

    Thin Solid Films

    (2010)
  • X.Y. Zhu et al.

    Thin Solid Films

    (2011)
  • J.L. Bucaille et al.

    Thin Solid Films

    (2004)
  • B. Zhou et al.

    Diamond Relat. Mater.

    (2006)
  • S.I. Hosseini et al.

    Thin Solid Films

    (2011)
  • Cited by (0)

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