Preparation of superhard amorphous carbon films with low internal stress

Tetrahedral amorphous carbon (ta-C) films were prepared by pulsed laser deposition using a 248-nm excimer laser wavelength and up to 45 J/cm(2) laser pulse energy fluence. Fluences above 6 J/cm(2) and mean kinetic energies of the ablated species above 30 eV, respectively, as well as substrate temperatures below 100 degreesC were found to be necessary for the formation of ta-C films with high sp(3) percentage. Such films are completely amorphous and have up to 85% sp(3) bonds. As-deposited films show high compressive stresses in the range of 8-10 GPa. The possibilities to reduce those stresses by means of thermal and pulsed laser annealing were investigated. We found that both methods allow the preparation of nearly stress-free diamond-like carbon films with several micrometers of thickness and good adherence to Si and WC hard metal substrates. The Vickers microhardness of those films was measured to be 55-65 GPa and the Young's modulus was measured to be 800-900 GPa by using a dynamic indentation method. (C) 2004 Elsevier B.V. All rights reserved.