AVS 49th International Symposium
    Surface Engineering Tuesday Sessions
       Session SE+NS-TuM

Paper SE+NS-TuM10
Preparation, Structure, and Properties of Composite Fullerene-Like CNx Films Produced by Pulsed Laser Ablation

Tuesday, November 5, 2002, 11:20 am, Room C-111B

Session: Nanocomposite and Nanolayered Coatings
Presenter: A.A. Voevodin, Air Force Research Laboratory
Authors: A.A. Voevodin, Air Force Research Laboratory
J.G. Jones, Air Force Research Laboratory
J.S. Zabinski, Air Force Research Laboratory
Zs. Czigany, Linkoping University, Sweden
L. Hultman, Linkoping University, Sweden
Correspondent: Click to Email
Production of composite CNx films made of fullerene-like structures in an amorphous matrix using laser ablation of graphite in nitrogen is reported. Deposition was optimized based on investigations of chemistry, excitation stage, kinetic energy, temperature, and spatial distributions of molecular (CN and C2) and atomic (C and N) species, using element specific imaging, time-of-flight experiments, fluorescence spectroscopy, and molecular vibration sequence analyses. Studies showed the importance of plume / substrate interaction in generating excited CN and C2 molecules with high vibrational energy at the condenasation surface for low deposition pressures. Films were characterized with x-ray photoelectron spectroscopy, Raman spectroscopy, high-resolution transmission electron microscopy, nanoindentation, and stress analyses. Nitrogen content directly depended on the concentration of CN radicals at the condensation surface. Formation of fullerene-like structures required a high vibrational temperature of these radicals, which was maximized at about 4 eV for depositions at 10 mTorr N2 and laser fluences of ~7 J/cm2. The presence of C2 had only a minor effect on film composition and structure. Optimization of plasma characteristics and a substrate temperature of 300 C helped to produce about 1000 nm thick solid films of CNx (N/C ratio 0.2 - 0.3) and pure carbon consisting of fullerene-like fragments and packages. Films exhibited elastic recovery of about 80%, elastic modulus of 160-250 GPa and hardness of up to 30 GPa, which was twice that of fullerene-like carbon films. The unusual combination of high elasticity and hardness was explained by cross-linking of fullerene fragments induced by the incorporated nitrogen. Correlations between plasma composition, film structure and properties are established. Results of film mechanical testing demonstrate benefits of the film application as a hard protective coating to resist brittle fracture at high contact loads.