Deposition of BC/ta-C Multilayer Thin Films by Laser Ablation

We deposited amorphous multilayer thin films of boron carbide (BC) and tetrahedral amorphous carbon (ta-C) by pulsed laser deposition (PLD) using B4C and graphite targets at room temperature. The laser beam (266 nm, 4-5 ns pulse width) from a Q-switchd Nd:YAG laser was used to irradiate the targets at a constant laser fluence of 4 J/cm2. The multilayer films consisted of bilayer structures with a bilayer period in the nanometric range (1-128 nm). The hardness of BC/ta-C multilayer thin films measured by a nanoindentation technique were between 38 and 48 GPa, dependent on the thickness of the layer. The highest hardness value was obtained for = 8 nm. The coefficient of friction was in the range 0.1-0.27, which is lower than that of BC single-layer films (>1.0). We also deposited amorphous multilayer thin films of boron nitride (BN) and ta-C to compare with BC/ta-C multilayer thin films.