Thick stress-free amorphous-tetrahedral carbon films with hardness near that of diamond

We have developed a process for making thick, stress-free, amorphous-tetrahedrally bonded carbon (a-tC) films with hardness and stiffness near that of diamond. Using pulsed-laser deposition, thin a-tC films (0.1-0.2 mu m) were deposited at room temperature. The intrinsic stress in these films (6-8 GPa) was relieved by a short (2 min) anneal at 600 degrees C. Raman and electron energy-loss spectra from single-layer annealed specimens show only subtle changes from as-grown films. Subsequent deposition and annealing steps were used to build up thick layers. Films up to 1.2 mu m thick have been grown that are adherent to the substrate and have low residual compressive stress (<0.2 GPa). The values of hardness and modulus determined directly from an Oliver-Pharr analysis of nanoindentation experimental data were 80.2 and 552 GPa, respectively. We used finite-element modeling of the experimental nanoindentation curves to separate the "intrinsic" film response from the measured substrate/film response. We found a hardness of 88 GPa and Young's modulus of 1100 GPa. From these fits, a lower bound on the compressive yield stress of diamond (similar to 100 GPa) was determined. (C) 1997 American Institute of Physics. [S0003-6951(97)00852-8].