Microstructure and Wear Resistance of Doped Diamondlike Carbon Prepared by Pulsed Laser Deposition
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331 Mat. Res. Soc. Symp. Proc. Vol. 505 © 1998 Materials Research Society
level, will cause the film to bulge and peel off from the substrates. It thus places a seemingly insurmountable barrier to the application for thick DLC films. In the past, some efforts have been directed toward improving the adhesion of DLC films by depositing an interlayer between the DLC film and the substrate[4,6-8]. It was found that Cu/Cr appeared to provide the best adhesion[6]. However, the authors did not provide convincing evidence for their observations in light of the fact that there is a weak chemical bonding between carbon and copper, which as has been known leads to poor adhesion of diamond films to copper substrates. This paper is an attempt to investigate the microstructure and tribological behavior (wear resistance), with the focus being at reducing the compressive stress in DLC films deposited by PLD through incorporation of low concentration of metal atoms into the film, without affecting the DLC bonding characteristics of the films. The emphasis is laid on the novel and simple way such that these metallic dopants can be incorporated into the growing DLC films via PLD. EXPERIMENTAL PROCEDURE To incorporate metallic dopants into the DLC films, the target configuration schematically illustrated in Fig. 1 was adopted. During the course of pulsed laser deposition, the target was spinning and the focused laser beam would impinge sequentially on graphite and metal portions to ablate the target materials to form a composite film. Copper and 1Piece titanium were chosen as dopants because a copper interlayer between the substrate and the DLC film has been considered to improve the adhesion of the Pure Graphite %% film though Cu is not a carbide former, while Ti is a Target Pellet were wafers (100) silicon The former. strong carbide Fig. I Schematic illustration of the target used as substrates, which were cleaned in acetone configuration used in this investigation and methanol ultrasonic baths followed by HF dip to remove the native oxide layer before loading into the laser deposition chamber. The laser beam source used was KrF pulsed excimer laser (X=248 nm, ts=25ns) at a repetition rate of 10 Hz, with an energy density close to 3.0 J/cm 2. All the depositions were conducted at room temperature in a high vacuum exceeding 1x10 7 torr for 40 minutes, producing an approximate film thickness of -240 nm. The films were then analyzed using Raman spectroscopy and x-ray photoelectron spectroscopy (XPS) for bonding characteristics and Rutherford backscattering spectroscopy (RBS) for chemical composition. Transmission electron microscopy was used to study the microstructure, with radial distribution function analysis and coordination defect information obtained from the diffraction patterns. A "crater grinding method" based upon microabrasion was used to measure the wear rate and to study the comparative wear characteristics of the samples.
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RESULTS AND DISCUSSIONS Fig.2 shows the RBS results for three samples, i.e. pure DLC, DLC+Cu
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