Characterization of metal-containing amorphous hydrogenated carbon films
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H. Dimigen and H. Hubsch Fraunhofer-Institut fiir Schicht- und Oberfldchentechnik, Vogt-Kolln-Strafie 30, D-2000 Hamburg 54, Germany (Received 8 April 1991; accepted 4 November 1991)
Metal-containing amorphous hydrogenated carbon (Me-C: H) films were prepared on silicon substrates. Two kinds of metals (Ti, Ta) were incorporated in the process of reactive rf diode— (13.56 MHz) and DC-magnetron sputtering, respectively. Elastic recoil detection (ERD) and Rutherford backscattering (RBS) of MeV He+ ions were used to determine the hydrogen content and mass density of Me-C: H films. The mechanical properties, i.e., microhardness, Young's modulus, and adhesion, were measured with the help of a nanoindenter and scratch tester. Results show that (1) the mechanical properties of Me-C: H films depend mainly on metal concentrations. At a certain metal concentration, optimal hardness, Young's modulus, and critical load were obtained; (2) the Me-C: H films with an optimal metal concentration possess similar hardness, Young's modulus, and higher critical load compared with the corresponding values of diamond-like carbon (a-C: H) films, due to the improvement of the toughness of the films by the incorporation of metals. Therefore, Me-C: H films show high promise of being wear-resistant protective coatings.
I. INTRODUCTION
Diamond-like carbon (a-C: H) films have been well studied and numerous works about their preparation,1"3 chemical,4-5 optical,6'7 electrical,8"10 and mechanical11'12 properties have been published. These films have high hardness, chemical inertness, and low sliding coefficient of friction. However, their high internal stress and insufficient adhesion on many substrates have also been found to limit their practical application, especially as wear-resistant coatings. To solve these problems Dimigen and Hubsch13'14 suggested the incorporation of metals into the a-C:H films. They found that metalcontaining hydrogenated carbon (Me-C:H) films possess excellent tribological properties, namely small, humidity-independent friction coefficients, low adhesive and abrasive wear, no counterpart-material transfer, negligible slip-stick, and low deposition temperatures (100-200 °C).15 In this work Ti-C: H and Ta-C: Hfilmswith various concentrations of metals were prepared on silicon wafer substrates by reactive rf diode and DC-magnetron sputtering, respectively. The dependence of the properties of Me-C: H films on metal concentrations was studied.
sputtering (13.56 MHz). Figure 1 shows schematically the experimental equipment. The rf voltage was applied via a tantalum carbide target with the vacuum chamber grounded. Before each deposition the substrate was plasma etched and the target was presputtered in pure argon (2.0 Pa) at -1.5 KV target bias and -800 V substrate bias. A grounded shutter was placed between both electrodes. In order to improve the film adhesion, first a thin Ta layer about 0.7 /xm thick was deposited on a Si wafer substrate after removing the shutter and changing the substrate bias to +20 V. The acetylen
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