Nanomechanical Properties of Amorphous Carbon and Carbon Nitride Thin Films Prepared by Shielded Arc Ion Plating
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resistance of the films were evaluated based on nanoindentation. These nanomechanical properties of the a-C:N and a-C films were compared and discussed in terms of the preparation conditions and chemical structures of the films. EXPERIMENTAL
An ion plating apparatus used in this study is schamattically depicted in Fig. 1. A sintered graphite target (Toyo Tanso IG5 10, ash 10 ppm), 64 mm in diameter and 32 mm in thickness, was mounted on a target holder and served as a cathode. Arc discharge was generated in Ar or N2 gas at a pressure of 1 Pa in order to synthesize a-C or a-C:N, respectively. A cathodic direct current at the target was maintained at 60 A. Si(100) wafers of 10 mm x 30 mm with 0.5 mm in thickness were used as substrates. Films of 150 nm in thickness were prepared onto these substrates, to each of which a dc bias voltage of 0 - -500 V was applied during deposition. In general, macroparticles generated at arc discharge points on the target frequently arrive at the substrate surface. Accordingly, such particles significantly degrade a deposited film. In order to reduce the macropar-
M.FC Substrate
Shielding Plate V
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Ar N2 Iron Plate Graphite
Pump
Magnet
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-t
DC Power Supply
Substrate DC Bias Voltage Supply
Fig. 1 Shielded arc ion plating
A
Diamond tip
titles on the substrate, a shielding plate of
stainless steel was inserted between the target and the substrate, as be described previously in detail [6]. The chemical compositions of the a-C:N films and chemical bonding states of both the a-C and a-C:N films were analyzed by X-ray photoelectron spectroscopy (XPS, ShimazuKratos, AXIS) using MgKa radiation. The hardness of the films was measured by a nanoindenter (Hysitron, TriboScope) interfaced with an atomic force microscope (AFM, Park Scientific Instruments, Autoprobe-LS). A Berkovich-type diamond tip whose radius was less than 100 nm was used for the measurement. A force-displacement curve of each sample was measured at a peak load force of 250 g.tN. Loading, holding and unloading times for each indentation were 2.5,
B I nm
2
1
2 pim
Fig. 2 A) Schematic illustration of the wear test B) A wear profile of an a-C film.
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0 and 2.5 s, respectively. The hardness of each film was determined from five measurements [15]. The wear resistance of the film was analyzed as schmatically illustrated in Fig. 2A. First, each film surface was scanned with a diamond tip at a constant load force of 20 RiN. The tip-scanning was repeated 30 times in a I jim-square region with 512 lines at a scanning rate of 2 jim/s. After this tip-scanning, the wear profile of the film was acquired using the indenter in the AFM mode at a contact force less than 5 jiN using the identical Berkovich tip. The profile shown in Fig. 2B was acquired on an a-C film prepared at Vs = -100 V. The central scanned region of I gm x I jim was worn and depressed from the surrounding unscanned region. Its wear depth was estimated to be less than 1 nm. We were able to distinctly detect a wear depth in sub-nm scale. Wear depths of co
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