Nanoindentation and Nanowear Studies of Thin Carbon Coatings
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217 Mat. Res. Soc. Symp. Proc. Vol. 505 01998 Materials Research Society
Since the thickness of the overcoats may soon be further reduced to 5-10 nm, nanotribological and nanomechanical characterization are believed to be critical in determining their tribological performance and optimizing the process parameters. In this respect nanoindentation test, 9 nanowear' 0 and scratch resistance 1 1 tests have been found to be of extreme value to evaluate the coating properties. The purpose of this paper is to present the results of wear performance and mechanical properties of a-C and CN thin overcoatings on silicon. EXPERIMENTAL Thin film carbon coatings were deposited on silicon using a Facing Target Sputtering (FTS) system.' 2 The background pressure of the FTS system was less than 5 x 10-7 Torr. The sputtering gas pressure was maintained at 0.5 mTorr. The a-C films were deposited on Si(100) substrate in pure Ar sputtering gas; the CN films were deposited on Si(100) substrate in a mixed gas of 0.2 mTorr Ar and 0.3 mTorr N2 .The deposition rate for both a-C and CN films was approximately 1 A/s. The films replicated the topography of the surface with rms roughness of less than 0.5 nm. Nanoindentation Test: Nanoindentation of thin-coated system requires indentation to be performed at shallow depths usually in the nanometer scale regime. A nanoindentation system with a three-plate transducer with electrostatic actuation and capacitive sensor developed by Hysitron Inc. to make loaddisplacement measurements with sub-nanometer sensitivity was used in present study.' 3 This system when used in conjunction with a commercial Atomic Force Microscope (AFM) provides in-situ images of the indents. The load-displacement curves obtained provide a "mechanical fingerprint" of a material's response to deformation, from which parameters such as hardness (H) and Young's modulus of elasticity (E) can be determined. In determining H and E however, a tip-shape calibration which relates the projected area (A) to the contact depth (he) needs to be carried out. This procedure is based on the method suggested by Oliver and Pharr. 14 Using a 90' 3-sided pyramidal diamond indenter, several indentations in standard fused silica sample (E = 72.0 GPa) at various contact depths were performed. A plot of load-displacement curves in 8007 Sample: Fused Silica fused silica in the depth range of 5-200 700-
nm is shown in Fig. 1 below. Note the loading portion of the curve overlay on
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each other, which shows excellent reproducibility of the system with no drift over the length of the experiment. From each of the curves, the projected was calculated. A plot of the computed area as a function of contact depth is plotted and a fitting procedure is employed to fit the (A) versus (hJ)data to a fifth order polynomial of the form
Displacement (nm)
Fig. 1 Load-displacement curves for fused silica at various contact depths A=2.598h'+Cih,+C2h 1+..3.hc -2 1/4 +C hc
Data Loading...
