Papers

ICMCTF2006 Session D2-2: Diamond and Diamond-Like Carbon Materials

Wednesday, May 3, 2006 8:30 AM in Room Sunset

Wednesday Morning

Start	Invited?	Item
8:30 AM		D2-2-1 The Versatility of Hot-Filament Activated Chemical Vapour Deposition L. Schäfer, M. Höfer (Fraunhofer IST, Germany) In the field of activated chemical vapour deposition (CVD) of polycrystalline diamond films hot-filament CVD is widely used for applications where large deposition areas are needed or three-dimensional substrates have to be coated. We have developed processes for the deposition of conductive, boron-doped diamond films as well as for tribological diamond coatings on deposition areas up to 50 cm by 100 cm. Such large area multi-filament processes are used to produce diamond electrodes for advanced electrochemical processes or large batches of diamond coated tools and parts, respectively. These processes demonstrate the high degree of uniformity and reproducibility of hot-filament CVD. The usability of hot-filament CVD for diamond deposition on three-dimensional substrates is well known for CVD diamond shaft tools. We also develop interior diamond coatings for drawing dies, nozzles, and thread guides. Hot-filament CVD also enables the deposition of diamond film modifications with tailored properties. In order to adjust the surface topography to specific applications we apply processes for smooth, fine-grained or textured diamond films for cutting tools and tribological applications. Rough diamond is employed for grinding applications. Multilayers of fine-grained and coarse-grained diamond have been developed, showing increased shock resistance due to reduced crack propagation. Hot-filament CVD is also used for the deposition of carbide and other non-diamond films. They may be applied e.g. as diffusion barriers to allow the separation of the substrate and the growing diamond film, avoiding interdiffusion and interfering reactions and promoting adhesion. In-situ deposition also enables the deposition of diamond-carbide composite layers which are used e.g. for improvement of adhesion and for stress engineering.
9:10 AM		D2-2-3 Comparative Study of Diamond-Like Carbon Films from Difference Chemical Sources S-.J. Park, K.-R. Lee (Korea Institute of Science and Technology, Korea) Plasma enhanced chemical vapor deposition (PECVD) method is one of the most relevant techniques for diamond-like carbon (DLC) coating. Various hydrocarbon gases such as methane, acetylene, or benzene have been used as the precursor gas. However, the effect of the chemical structure of the precursor molecule is yet to be fully understood. In the present work, DLC films deposited from glow discharge of n-hexane(C₆H₁₄) and benzene(C₆H₆) were compared in detail. These molecules are significantly different in the chemical structure although the number of carbon atoms in the molecule is the same: n-hexane has the straight-chain alkane structure while benzene has aromatic ring structure. Hydrogenated diamond-like carbon films were deposited on Si (100) wafer using 13.56MHz r.f PACVD. The bias voltage was systematically changed from -200V to -800V. The growth rate and the residual stress and hardness of the films were measured and the structure of the film was characterized using Raman and FT-IR. The growth rate of the DLC film from benzene was much higher than that of the DLC film from n-hexane. But the residual stress and hardness of DLC film from n-hexane were much higher than those of DLC film from benzene, showing maximum point at bias -500V. From the FT-IR spectra, the DLC film from benzene had more sp¹ C-H bond and sp² C-H bond than the DLC film from n-hexane. The differences would result from the difference in the plasma decomposition behavior of the precursor molecules. The present results suggested that n-hexane was decomposed into lighter ionized molecules in the glow discharge, resulting in higher kinetic energy per carbon atom.
9:30 AM		D2-2-5 Predicted Thermal-Mechanical Properties of Carbon Nanostructures: Fullerenes vs. Diamondoids D.W. Brenner (North Carolina State University); O.A. Shenderova (International Technology Center) Carbon nanostructures have been targeted for a number of mechanical and thermal management applications due to there high modulus and thermal conductivity, respectively. Although most of the emphasis has been on fullerene-like structures such as fullerene nanotubes, diamond nanorods and related diamondoid structures hold equal promise for many applications. We have been using molecular modeling to predict the mechanical and thermal transport properties of a wide range of carbon-based nanostructures. For example, although pristine fullerene nanotubes are predicted to have a higher tbermal conductivity than diamond nanorods of similar diameters, the thermal conductivities of nanotubes are much more reduced by surface functionalization than are diamond nanorods, making the latter attractive for applications in which heat is transferred from a matrix to a carbon nanostructure via cross-linking. This and similar phenomena, including non-equilibrium heat transport, will be discussed.
10:10 AM		D2-2-7 The Characteristics of Diamond-Like Carbon Film Deposited by Filter Arc Deposition K.-W. Weng (Mingdao University, Taiwan); S. Han (National Taichung Institute of Technology, Taiwan); Y.-C. Chen (National Chung Hsing University, Taiwan); D.-Y. Wang (Mingdao University, Taiwan); H.-C. Shih (National Tsing Hua University, Taiwan) Diamond-like carbon (DLC) film was successfully deposited on SKD 51 by filter arc deposition (FAD) in this study. An interlayer of Cr/CrN between the substrate and DLC film was formed, which enhanced the adhesion and the mechanical properties of the film assembly. A magnetic field built for filtering was found to be effectively preventing from the macroparticles incorporation during the deposition of DLC films. High sp³ bonding of the film structure was obtained at an optimal condition through the varying of the bias voltage and current. To compare the process parameters, various mechanical properties of the deposited films were studied, e.g. hardness, adhesion and wear behavior. The crystal structure was investigated by using x-ray diffraction (XRD) and transmission electron microscopy (TEM). While, the surface morphology and chemical composition of films were studied by field emission scanning microscopy (FESEM), x-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. The major contribution of this study is to be able to deposit a well intact DLC films with good adhesion by developing an economic process for the enhancement of the mechanical properties of the DLC film assembly on the SKD 51.
10:30 AM		D2-2-8 Friction and Wear Behavior of Amorphous Hard Carbon (ta-C) Coatings Under Different Lubrication Conditions Ch. Kleemann, H.-J. Scheibe, T. Schuelke (Fraunhofer USA, Inc.) Using the Laser-Arco technology (high-current pulse-arc techniques), ta-C films with thick-nesses between 1 and 12 µm and an average hardness of about 40 GPa have been depos-ited onto steel substrates under industrial deposition conditions. The films are characterized with respect to their density, elastic modulus, adhesion and surface roughness in a range between Ra » 20 nm (polished) and maximum Ra » 150 nm (as deposited). Their friction and wear behavior was studied with a Pin-on-Disk tribometer in the reciprocating module configu-ration. Different lubrication conditions (dry / 50% humidity and using a typical engine oil Val-voline SAE10W30) are applied in the tests against different ball materials (bearing steel, sap-phire and hard metal) with commercially available surface quality. The loads on the balls were selected that a comparable contact pressure in the range between 800 and 2,400 MPa could be realized. Run-in effects were separated from the stationary behavior by tests with a large number of cycles (106) corresponding to a distance of 1,000 m. In all tests the friction was determined during the test, the wear rate was determined after the test for the ball and for the coated disk. The wear behavior depends on the hardness of the counter body material, the surface roughness of the ta-C coating and the lubrication condi-tions. The highest wear resistance and lowest friction coefficient is found in friction pairs with comparable hardness at all lubrication conditions. Under dry running conditions the smooth-ness of the surfaces plays an important roll.
10:50 AM		D2-2-9 Hydrophobic and Wear Resistant Amorphous Carbon Based Multilayer Coatings K. Bewilogua, I. Bialuch, H. Ruske (Fraunhofer IST, Germany) By adding elements like Si, O or F, diamond-like carbon films (a-C:H) can be considerably modified. For instance silicon containing a-C:H:Si is known for friction coefficients which are clearly lower than those of pure a-C:H. Highly hydrophobic coatings can be realized by incorporation of Si and O (a-C:H:Si:O). However, an optimization of one property mostly leads to a deterioration of other properties. Thus highly hydrophobic films commonly have a low wear resistance. We tried to overcome this relation by multilayer coatings. Such coatings consisting of a-C:H and a-C:H:Si:O single layers were prepared by a mid frequency glow discharge process using alternately methane and hexamethyldisiloxane (HMDSO) as precursor. The number of layer packs (1 pack consists of 1 a-C:H and 1 a-C:H:Si:O layer) was varied between 1 and 36 while the total coating thickness was kept nearly constant in a narrow range around 3.5 µm. For 3 to about 10 layer packs rather low abrasive wear rates, not far from that of pure a-C:H, were measured. On the other hand, the hydrophobicity remained quite near to those of a-C:H:Si:O. Important was the material (a-C:H or a-C:H:Si:O) and also the thickness of the top layer. A further reduction of the abrasive wear rates could be achieved with a modified deposition regime where the methane flow was constant and only the HMDSO flow was alternately varied. The coating adhesion could be markedly improved if a duplex process was used starting with a plasma nitriding step. Investigations by Secondary Ion Mass Spectroscopy and Scanning Electron Microscopy were carried out to prove the distinction of both phases in the layer packs.
11:10 AM		D2-2-10 Super-Hydrophobic and Low Wetting Angle Hysterisis Surface Controlled by a-C:H:Si:O Film Deposition and Nano Structuring of Si Surface : Double Rough Structure and Free Energy Calculation T.-Y. Kim (Korea Institute of Science and Technology, Korea); I. Bialuch, K. Bewilogua (Fraunhofer IST, Germany); K.-H. Oh (Seoul National University, Korea); K.-R. Lee (Korea Institute of Science and Technology, Korea) By combining nanoscale surface structuring of Si with a hydrophobic a-C:H:Si:O coating, we generated the super-hydrophobic surface with very low wetting angle hysteresis. Nanoscale undulated Si surface was prepared by CF₄ plasma etching using nano-sized metal dots as the mask. The size and distribution of the metal dots were controlled by the thickness of the metal film, which made it possible to manipulate the surface structure of Si in a systematic manner. The a-C:H:Si:O film was deposited by the r.-f. PECVD using mixtures of hexamethyldisiloxane (HMDSO) and Ar as the precursor gas. Wetting angle of pure water on the smooth surface of this film was varied from 60 to 100° by changing the composition of the supplied gas mixture. We observed that a double rough structure is very efficient to make a super-hydrophobic surface. Wetting angle of pure water on the double rough surface was 165° with the wetting angle hysteresis (the angle difference between forwarding and receding angle) less than 5°. Free energy calculation of a simplified rough surface proposed a criterion for rough surface design that can be applied to the moving droplet applications.
11:30 AM		D2-2-11 Plasma Biasing to Control the Growth Conditions of Diamond-Like Carbon A. Anders (Lawrence Berkeley National Laboratory); N. Pasaja (Chiang Mai University, Thailand); S.H.N. Lim (Lawrence Berkeley National Laboratory); T.C. Petersen, V.J. Keast (University of Sydney, Australia) It is well known that the bonding structure of diamond-like carbon, and in particular the sp²/sp³ ratio, can be controlled and tuned by the energetics of the condensing carbon ions or atoms, and films assisting ions, if present. In many cases, the energy of ions arriving at the surface of the growing film is determined by the bias applied to the substrate. The bias causes a sheath to form between substrate and plasma in which the potential difference between plasma potential and surface potential drops. In this contribution, we demonstrate that the same results can be obtained with substrates that are grounded or not biased by shifting the plasma potential. This "plasma biasing" is shown to work well with pulsed cathodic carbon arcs, resulting in tetrahedral amorphous carbon (ta-C) films that are comparable to films obtained with the more conventional substrate bias. To verify this, ta-C films made by conventional bias and plasma bias were characterized by transmission electron microscopy (TEM) and electron energy loss spectrometry (EELS). This work was supported by the Thailand Research Fund, by the American Australia Association, and by the U.S. Department of Energy under Contract No. DE-AC02-05CH11231.