Characterization of composite carbon coatings deposited by dc cathodic arc technique
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I. INTRODUCTION
II. EXPERIMENTAL
The possibility of depositing diamond-like carbon is considered to be associated with ion activation of filmforming processes. The variety of coating techniques is limited, however, by low thermal load capacity of many substrate materials as well as by fast rate deposition. Both enhanced ion activation and fast rate deposition at substrate temperatures below 200 °C are advantages of cathodic arc deposition techniques (CADT). Their application to carbon deposition has been reviewed recently.12 The main characteristics of these techniques are the erosion of a graphite cathode by the high power density of cathode spots typical of that discharge3 and the deposition of insulating films from the highly ionized carbon plasma of the arc discharge.2 Erosion products of the cathode are ions, macroscopic fragments of the cathode material and, to a negligible extent, also neutral carbon atoms.4 Means for separation of the macroparticles have been developed to avoid the incorporation of macroscopic graphitic fragments.5'6 CADT-deposited carbon coatings are reported to exhibit exceptional hardness and high electrical resistivity.1'7 The structure of carbon thin films deposited by dc CADT with particle separation is described in terms of a diamond-like short-range order of carbon atoms.1'8 The particle separation involves, however, decreased substrate current densities and thus lower growth rates of the films as well as smaller applicable deposition areas.1 In the present paper we report on first results of structural and tribological investigations of carbon films deposited by cathodic arc evaporation of graphite with controlled cathode spot position2 and without application of particle separators.
A. Deposition process
J. Mater. Res., Vol. 6, No. 1, Jan 1991 http://journals.cambridge.org
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The deposition process was performed in a vacuum chamber of 30 cm in diameter and 50 cm in length evacuated by a vacuum system with an oil diffusion pump. Figure 1 is a schematic view of the deposition apparatus used in our experiments. It consists of an evaporator assembly (1) suitable for the dc cathodic arc evaporation of graphite2 and a vacuum chamber (2) with a substrate holder (3). The substrates are mounted at a distance of about 30 cm from the cathode erosion face in close thermal contact to the water-cooled and dc/rf biased substrate holder of 12 cm in diameter. A high purity graphite cylinder of 5 cm in diameter served as a consumable cathode (4). The magnetic coils in Fig. 1 characterize the general principle applied to stimulate the cathode spot motion across the cathode erosion face by the application of external magnetic fields. Together with a suitable control unit, the coils are part of an evaporation source with controllable cathode spot position.2 In addition to the features of the deposition apparatus shown in Fig. 1, a shutter in front of the substrate holder serves to effect definite deposition cycles. The substrate materials applied in our experiments are liste
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