Mechanical properties of laser-assisted deposited amorphous carbon films
Mechanische Eigenschaften von Laser-unterstützt abgeschiedenen amorphen Kohlenstoffschichten
Amorphous hydrogen-free carbon films (a-C) combine the outstanding properties of diamond with those of the amorphous microstructure. Their main properties like hardness, Young's modulus and density depend on the ratio of sp3:sp2 bonded carbon atoms. a-C films were deposited with pulsed laser deposition (PLD) and laser-induced pulsed vacuum arc (Laser-Arc). These techniques generate a high energy plasma from a graphitic target material that enables films with a high content of sp3 bond (> 80 per cent), high hardness (up to 75 GPa), and Young's modulus E > 700 GPa to be deposited, depending on the deposition conditions. Comparable with the mechanical properties of diamond, superhard amorphous carbon films can be produced with these techniques. The corresponding technological optimization has been made possible by the permanent non-destruction control of film quality by the laser-acoustic technique. It yields to the Young's modulus, which represents the averaged bonding stiffness within t he film. The Young's modulus is shown to be a clear indicator of the sp3 fraction in DLC films. It correlates well with the results obtained by EELS, Raman spectroscopy and ellipsometry. A strong correlation was found between Young's modulus and density for DLC films.