THICK STRESS-FREE AMORPHOUS-TETRAHEDRAL CARBON-FILMS WITH HARDNESS NEAR THAT OF DIAMOND

We have developed a process for making thick, stress-free, amorphous-t etrahedrally bonded carbon (a-tC) films with hardness and stiffness ne ar 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 i n 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 an nealed specimens show only subtle changes from as-grown films. Subsequ ent 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 s ubstrate and have low residual compressive stress (<0.2 GPa). The valu es of hardness and modulus determined directly from an Oliver-Pharr an alysis of nanoindentation experimental data were 80.2 and 552 GPa, res pectively. We used finite-element modeling of the experimental nanoind entation curves to separate the ''intrinsic'' film response from the m easured substrate/film response. We found a hardness of 88 GPa and You ng's modulus of 1100 GPa. From these fits, a lower bound on the compre ssive yield stress of diamond (similar to 100 GPa) was determined. (C) 1997 American Institute of Physics. [S0003-6951(97)00852-8].