Effect of Film Thickness on the Nanoindentation Measurements of Hard Diamondlike Carbon Films Prepared by Pulsed Laser D

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EFFECT OF FILM THICKNESS ON THE NANOINDENTATION MEASUREMENTS OF HARD DIAMONDLIKE CARBON FILMS PREPARED BY PULSED LASER DEPOSITION Q. Wei, J. Sankar, A. K. Sharma* and J. Narayan* NSF Center for Advanced Materials and Smart Structures, Department of Mechanical Engineering, North Carolina A&T State University, Greensboro, NC 27411 *Department of Materials Science and Engineering, Burlington Labs, P. O. Box 7916, North Carolina State University, Raleigh, NC 27695-7916 ABSTRACT We have investigated the effect of film thickness on the nanoindentation measurements of hard diamondlike carbon (DLC) films. The DLC films were deposited on Si (100) substrates by pulsed excimer laser deposition (KrF, λ=248nm, duration=25 ns, energy density about 3.0 J/cm2, repetition rate 10 Hz) in high vacuum (~5x10-7 torr) at room temperature for various periods of time (from 5 minutes to 20 minutes). The thickness of the films was measured by optical profilometry, and ranges from 200 to 50 nm. The nanohardness and elastic modulus of these films were measured by a depth-sensing nanoindentation technique with NanoindenterXP. Preliminary experimental observations show that the nanoindentation results are a function of film thickness. Both the hardness and Young’s modulus versus displacement curves of the 200nm thick film exhibit a peak at around tenth of the film thickness. The rest of the samples with smaller film thickness show plateaus, which are higher than the hardness and Young’s modulus values of the substrate. INTRODUCTION Due to its wealth of atomic structure and properties, amorphous carbon has been drawing interest of research for the past two decades. The wide spectrum of the atomic structure and properties of amorphous carbon stems from the capability of carbon to form different hybridizations. Depending on the short-range environment, physical and mechanical properties of amorphous carbon can vary between the two crystalline extrema of carbon, i.e. graphite and diamond. When amorphous carbon mainly consists of tetrahedrally bonded carbon atoms, it is called diamondlike carbon (DLC), or tetrahedral amorphous carbon (t-aC). Highly tetrahedral carbon material can possess properties comparative to those of crystalline diamond. For example, the elastic modulus and hardness of crystalline diamond are about 1000 and 100 GPa, respectively [1]. The elastic modulus and hardness of mostly tetrahedral DLC can be as high as 700 and 70 GPa, respectively [2]. Further more, the mechanical and physical properties of DLC can be tailored with ease by changing the sp3/sp2 ratio. Combined with all the unique properties, DLC thin coatings have found wide applications such as tribological thin coatings that require chemical stability, good wear resistance and low coefficient of friction; infrared antireflective coatings; field emission sources for advanced flat panel displays; sensors; and so on [3,4]. About one decade ago, it was considered that the presence of hydrogen would be necessary to stabilize the sp3 bonding states and to saturate the dangling

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