ICMCTF2003 Session D3: Properties and Applications of Carbon-based Films
Thursday, May 1, 2003 1:30 PM in Royal Palm 1-3
D3-1 The Effect of Bonding Characteristics on the Properties of Sputtered Si-aC:H Thin Films
J.T. Glass (Case Western Reserve University); R. Evans, G. Doll (The Timken Company); J. Bentley, K.L. More (Oak Ridge National Laboratory)
A brief review of the effects of impurities on the properties of amorphous carbon will be presented, followed by a discussion of the authors’ research on silicon-incorporated amorphous carbon (Si-aC:H). Films with up to 18 atomic percent Si were deposited on silicon and steel substrates by reactive sputtering in an unbalanced magnetron sputtering system. A Ti interlayer was utilized to enhance adhesion of the films to the substrates. Si was incorporated into the film via the introduction of tetramethyl silane into the reaction chamber. The objective of this research was to correlate the atomic-scale structural and chemical characteristics of the films with various mechanical, optical and electrical properties of the films. Transmission electron microscopy revealed that the Si-aC:H phase is amorphous and TiC exists at the Si-aC:H/Ti phase boundary for all compositions. XPS measurements indicated that the C-C sp@super 3@ interlinked network decreased with increasing Si content, accompanied by an increase in C-H and Si-H bonds. Radial distribution functions obtained using extended electron energy-loss fine structure analysis (EXELFS) were also utilized to examine the changes in bonding caused by the Si incorporation. Changes in nearest neighbor distances and coordination numbers were determined and compared to various changes in the macroscopic properties of the films.
D3-3 Stress Control of ta-C Films without Deteriorating Hardness by Nanoscale Manipulation
C.-S. Lee (Korea Institute of Science and Technology and Yonsei University, South Korea); T.-Y. Kim (Korea Institute of Science and Technology and Seoul National University, South Korea); K.-R. Lee (Korea Institute of Science and Technology, Korea); K.H. Yoon (Yonsei University, South Korea)
High residual compressive stress of tetrahedral amorphous carbon (ta-C) films has been considered as one of the major obstacles for their applications. In addition to the film delamination or changes in physical properties, the characterization of the film is also affected by the residual stress. Many efforts have been thus focused on reducing the residual stress without deteriorating other physical properties, such as hardness. In the present work, we reported two approaches by nanoscale manipulation of the film structure. Nanoscale multilayer with alternating ta-C and Si incorporated ta-C layer were prepared by hybrid FVA process. Changing the thickness fraction of ta-C:Si layer could reduce the residual stress by 40%. Residual stress was also reduced by incorporating nano-sized Ni dots at the interface between the film and the substrate. The reduction was strongly dependent on the size of the Ni dots. TEM and Raman spectrum analysis shows that the nano-sized Ni dots results in nanoscale graphitic phase embedded in hard ta-C matrix. In both cases, degradation of mechanical properties was insignificant. The stress reduction mechanism will be discussed in terms of the changes in nano-scale film structure.
D3-4 Effects of Substrate Temperature on Bonding Structure and Mechanical Properties of Amorphous Carbon Films
S. Chowdhury, M. Laugier, Z. Rahman (University of Limerick, Ireland, RO)
Diamond-like carbon thin films were prepared at different substrate temperatures by RF magnetron sputtering of a graphite target. The chemical bonding of the carbon structure was characterized by Raman spectroscopy. Raman measurements showed that increasing the substrate temperature results in an increase in the sp@super 2@-bonded fraction of carbon atoms. Mechanical properties, namely hardness and Young's modulus, were determined by the nano indentation technique. The hardness and Young's modulus values both increased with increase of substrate temperature up to 120@super o@C and decreased thereafter. These results indicate that substrate temperature has a strong influence on the bonding properties of the deposited film and the changes in bonding ratio (sp@super 2@/sp@super 3@) were correlated with changes in the mechanical properties.
D3-5 Correlation of Tribological, Microstructural and Surface Properties of Co-a:C Films
D.H.C. Chua, W.I. Milne (Cambridge Univerisity, United Kingdom); B.K. Tay, P. Zhang, D. Sheeja (Nanyang Technological University, Singapore); X.-Z. Ding (Singapore Institute of Manufacturing Technology, Singapore)
Cobalt containing ta-C films were fabricated by filtered cathodic vacuum arc deposition (FCVA) system. The Co concentration was varied from 1% to 20% by atomic percentage in target with different deposition parameters used. The mechanical and microstructural properties of the films were systematically studied. Raman and XPS results confirm that different concentration of Co under different deposition parameters affect the sp3 content in the film. Tribological measurements show that the critical load was much better at higher Co concentration but the reverse was true for hardness. AFM studies of Co:ta-C films showed that surface roughness was very low in the range of (5-10nm) irregardless of the Co concentration.. Contact angle measurements confirm that the surface energy of the films vary depending on various deposition parameters. Such metal composite coatings exhibit reduced stress, thus enabling deposition of relatively thick coatings while retaining good hydrophobicity and acceptable hardness and Young's modulus. By correlating all the data together, an optimum window could be found for various application-specific properties required.
D3-6 The Study of Dynamic Balance Deposition Effect of Metal Containing Amorphous Carbon Films
P. Zhang, B.K. Tay, J.Y.SZE Sze, Y.S. Liu, G.Q. Yu, D. Sheeja, Z.W. Zhao, S.P. Lau, C.Q. Sun (Nanyang Technological University, Singapore)
It is known that filtered cathode vacuum arc (FCVA) technique can deposit tetrahedral amorphous carbon (ta-C), which has interesting and useful properties because of the high sp@super 3@ fraction of carbon atoms (up to 87%) in the film. By incorporating metal elements into these ta-C films, some properties will greatly enhanced, such as Al, Ti incorporation can low the stress of the films while the hardness is still high, Al incorporation can low surface energy of the films, Ti, Co incorporation can improve the field emission properties of the films. @paragraph@It is observed that the metal composition of the metal containing amorphous carbon (a-C:Me) films deposited with negative 80 V bias varies from that of its corresponding metal/carbon target. It can be seen that the metal composition of a-C:Ti films is much higher (>2 times) than its corresponding target, while the metal composition of a-C:Al films is much lower (<0.5 times) than its corresponding target. We attribute this observation to the dynamic balance deposition (DBD), a balance between the deposition and self-sputtering, effect during the FCVA deposition process. @paragraph@It is important to study the factors which affect the metal composition of the a-C:Me films because many properties of these films are related to the type and amount of metal composition in the film . In this paper, a study of the metal composition as a function of substrate bias for the a-C:Al and a-C:Ti will be presented.
D3-7 Tedrahedral Amorphous Carbon as a Bio-mechanical Coating - Current Status
V-M. Tiainen, A. Anttila (University of Helsinki, Finland)
High quality ta-C coatings are a very promising approach for improving the wear resistance and the biocompatibility of human implants. In our recent hip simulator tests ta-C coating improved the wear resistance of the hip joint by a factor of 10@super 6@ compared with conventional ones. The 15000000 walking cycle tests equivalent to 15 years of clinical use were performed using Paul gait load profile with 3000 N peak load and bovine serum as the lubricant@footnote 1@. The 40-100 µm ta-C coatings were deposited with Filtered Pulsed Arc Discharge (FPAD) method developed in our laboratory@super 2,3@. These results are in good agreement with our earlier experiments@super 4@. On a commonly used CoCrMo alloy 1 µm ta-C decreased the corrosion rate of the substrate by a factor of 10@super 5@ when exposed to a saline solution equivalent to the body fluid in 37@super o@C for two years. According to various investigations conducted in different laboratories ta-C coatings seem to have a benign biological response. Usually the bone cell to implant bonding is improved whereas the tendency for blood clot formation is diminished. However, the biological response of ta-C can be tailored by doping or by changing the film quality. These aspects will be reviewed. @paragraph@@super 1@R. Lappalainen, M. Selenius, A. Anttila, Y.T. Konttinen, S.S. Santavirta, Reduction of Wear in Total Hip Replacement Prostheses by Amorphous Diamond Coatings, accepted for publication in Applied Biomaterials.@paragraph@ @super 2@A. Anttila, R. Lappalainen, V-M. Tiainen and M. Hakovirta, Superior attachment of high-quality hydrogen-free amorphous diamond films to solid materials, Advanced Materials, 9(1997)1161-1164. @paragraph@@super 3@ A. Anttila, J-P. Hirvonen, J. Koskinen, US Patent 5 078 848, 1992.@paragraph@@super 4@ A. Anttila, R. Lappalainen, H. Heinonen, S. Santavirta and Y. T. Konttinen, Superiority of Diamondlike Carbon Coatings on Articulating Surfaces of Artificial Hip Joints, New Diamond and Frontier Carbon Technology, 9(1999)283-288.
D3-9 Deposition of Diamond-like Carbon Films on Aluminium Substrates by RF-PECVD Technique: Influence of Process Parameters
N. Ravi (International Advanced Research Centre, India); V.L. Bukhovets, I.G. Varshavskaya (Russian Academy of Sciences, Russia); G. Sundararajan (International Advanced Research Centre for Powder Metallurgy and New Materials, India)
The properties of Diamond-like carbon (DLC) films are highly influenced by the properties of the substrate on which they are deposited. The DLC coatings have largely been carried out on hard substrate materials such as glass, steel and silicon. In contrast, DLC coatings on soft substrates such as polymers, aluminium, copper and titanium have been quite limited and in such cases techniques like Plasma immersion ion implantation (PIII), Laser assisted CVD, ion beam have been employed. Deposition of DLC films on aluminium has drawn recent attention owing to its many potential applications such as automobile pistons, bores, VCR heads, copier machine drums, textile components etc. It can be inferred that practically no literature is available with regard to deposition of DLC films exclusively on aluminum by utilizing RF-PECVD technique. @paragraph@In our experiments, DLC films have been deposited on commercial pure (c.p.) aluminium in a 250 kHz RF glow discharge sustained by methane gas in an asymmetric (small powered electrode and large grounded electrode) CVD reactor. The present study has been conducted to assess the influence of different process parameters such as the bias voltage, ion current density, methane gas flow rate and its pressure, deposition temperature and inter-electrode distance on the rate of deposition of DLC on c.p. aluminium. The density and thickness of these DLC coatings have been evaluated. Additionally, on selected samples, the tribological tests have been performed to evaluate their friction behaviour. The results from the above study will be presented and rationalized on the basis of existing models for DLC deposition.