Papers

ICMCTF2009 Session D2-1: Diamond and Diamond-Like Carbon Materials

Monday, April 27, 2009 10:00 AM in Room Royal Palm 4-6

Monday Morning

Start	Invited?	Item
10:00 AM		D2-1-1 Preparation and Comparison of a-C:H Coatings using Reactive Sputter Techniques M. Keunecke, K. Weigel, K. Bewilogua (Fraunhofer Institute for Surface Engineering and Thin Films, Germany); R. Cremer (CemeCon A.G., Germany); H.-G. Fuss (Cemecon AG, Germany) Amorphous hydrogenated carbon (a-C:H) coatings are widely used in several industrial applications. These coatings commonly will be prepared by plasma activated chemical vapor deposition (PACVD). The mainly used method to prepare a-C:H coating in industrial scale bases on a glow discharge in a hydrocarbon gas like acetylene or methane using a substrate electrode powered with medium frequency (m.f. - some 10 to 300 kHz). Some aims of further development are adhesion improvement, increase of hardness and high coating quality on complex geometries. A relatively new and promising technique to fulfill these requirements is the deposition of a-C:H coatings by a reactive d.c. magnetron sputter deposition from a graphite target with acetylene as reactive gas. An advancement of this technique is the deposition in a pulsed magnetron sputter process. Using these three mentioned techniques a-C:H coatings were prepared in the same deposition machine a Cemecon CC 800/9. For adhesion i mprovement different interlayer systems, e.g. CrN were applied. The effect of different substrate bias voltages (d.c. and d.c.pulse) was investigated. Applying magnetron sputter technique in the d.c. pulse mode, micro hardness values up to 40 GPa could be reached. Beside the hardness other mechanical properties like resistance against abrasive wear and adhesion were measured and compared. Cross sectional SEM images showed the growth structure of the coatings. The coating process capability will be demonstrated with images of coated mills.
10:20 AM		D2-1-2 Effect of Boron Incorporation on the Structure and Electrical Properties of Diamond-Like Carbon Films Deposited by Femtosecond and Nanosecond Pulsed Laser Ablation A. Sikora (Université Jean Monnet, France); O. Bourgeois, J.L. Garden (CNRS et Université de Grenoble, France); J.N. Rouzaud (Ecole Normale Supérieure, France); J.C. Sanchez-Lopez, T.C. Rojas (Instituto de Ciencia de Materiales de Sevilla, Spain); A.S. Loir, F. Garrelie, C. Donnet (Université Jean Monnet, France) The influence of the incorporation of boron in Diamond-Like Carbon (DLC) films on the microstructure of the coatings has been investigated. The a-C:B films have been deposited at room temperature in high vacuum conditions, by ablating graphite targets either with a femtosecond pulsed laser (800 nm, 150 fs, femto-DLC), or with a nanosecond pulsed laser (248 nm, 20 ns, nano-DLC). Doping with boron within the range 2-8 % has been performed by ablating alternatively graphite and boron targets. The film structure and composition have been highlighted by coupling Atomic Force Microscopy, Scanning Electron Microscopy, Electron Energy Loss Spectroscopy and High Resolution Transmission Electron Microscopy. Using the B K edge, EELS characterization reveals the boron effect on the carbon bonding. Moreover, the plasmon energy reveals a tendency of graphitization associated to the boron doping. The boron particles synthesized by femtosecond PLD have been characterized by HRTEM and reveals that the particles are amorphous or crystallized. The nanostructure of the boron doped nano-DLC and the boron doped femto-DLC are thus compared. In particular, the incorporation of boron in the DLC matrix is highlighted, depending on the laser used during deposition. Electrical measurements will show that some of these films have potentialities to be used in low temperature thermometry (77-300 K range), considering their conductivity and temperature coefficient of resistance (TCR).
10:40 AM		D2-1-3 Retrospective Lifetime Prediction of Failed and Explanted DLC Coated Hip Joint Balls G. Täger, L.E. Podleska (University Essen, Germany); C.V. Falub, G. Thorwarth, M. Stiefel, R. Hauert (Empa, Switzerland) Background Particle induced osteolysis is still a maior concern in total hip arthroplasty. Numerous efforts are made to improve tribogy and reduce wear induced particles which cause subsequent inflammation and implant loosening. One of these modifications is thin film coating of the bearing surfaces using diamond like carbon coatings. Materials&methods In a consecutive trial 101 DLC-coated femoral heads (DLC-group) and another 101 femoral heads consisting of Al₂O₃, both articulating against polyethylene cups, were implanted. Patients were comparable for age, gender, activity index and indications. Surgery followed a standard protocol. There were no further differences regarding design, cementless fixation or any other surgical issue. Results Survivorship analysis for aseptic loosening 8.5 years following implantation resulted in a significant difference between both groups with a 54% survival for DLC/PE compared to 88% for Al₂O₃/PE bearings (p <0.001). SEM showed delamination of the carbon layer which caused excessive debris of polyethylene and in some cases even of the metallic substrate of the heads XPS depth profiling and cross sectional SEM analysis performed on the explanted DLC coated TiAlV hip joint balls revealed that the coating consists of several DLC-Si layers with an adhesion promoting Si interlayer on top of the TiAlV substrate. Using an adhesion determination technique a delamination speed of about 50 micrometer per year was estimated for the DLC coated TiAlV hip joints, in agreement with the size of the ob-served delaminated spots. High-resolution SEM monitoring of the Focused Ion Beam (FIB) transversal cuts in the vicinity of the delaminated spots revealed that the delamination of the DLC coatings is correlated with the in-vivo corrosion of the under laying adhesion promoting Si interlayer. Conclusion Despite the promising effects of thin film coatings, detailed investigation on the surfaces characteristics have to be performed prior to clinical use
11:20 AM		D2-1-5 Properties of Nanostructured Surfaces of DLC Thin Films Prepared by Pulsed-DC PECVD C. Corbella, S. Portal, M. Rubio-Roy, E. Bertran, M.C. Polo, E. Pascual, J.L. Andújar (University of Barcelona, Spain) Diamond-like carbon (DLC) thin films, which show attractive mechanical properties for their performance as hard and tribological coatings, have been prepared at room temperature by pulsed-DC plasma-enhanced chemical vapour deposition (PECVD). Previous to the deposition, substrate nanostructuring has been performed in order to tailor the surface properties of DLC. For that, spherical silica submicroparticles of between 300 and 500 nm diameter were synthesized by sol-gel method and deposited on silicon wafers by Langmuir Blodgett. After that, the samples were annealed to promote chemical bonds between the spheres and the substrate, and finally, DLC films with thickness equivalent to particle size were deposited. A systematic study of the surface properties has been performed: wettability (contact angle), friction coefficient (nanotribometer) and abrasive wear rate (Calotest) were evaluated to optimize substrate nanostructure and deposition parameters. Such surface modification is suitable for applications requiring protective coatings with tunable hydrophobicity.
11:40 AM		D2-1-6 Topography Development of Toluene Based a-C:H Coatings Deposited by RF-PECVD C. Hormann, S. Meier (Fraunhofer Institute of Mechanics of Materials IWM, Germany) PECVD deposition using toluene as hydrocarbon precursor gas has proven to be an efficient method to deposit amorphous hydrogenated carbon (a-C:H) films for tribological applications. These coatings feature an unusual surface topography compared to films deposited from conventional precursors like methane or acetylene. Mound-like structures on the nano- and micrometer scale develop early during film growth and show a distinct dependence on the initial substrate structure and the progress of deposition. We investigated this growth both experimentally and using continuum simulation models and present results which show that taking into account non-local self shadowing effects of the surface topography during deposition we can reproduce the experimentally observed behaviour in simulation.