Papers

ICMCTF2008 Session D2-1: Diamond and Diamond-Like Carbon Materials

Tuesday, April 29, 2008 1:30 PM in Room Royal Palm 4-6

Tuesday Afternoon

Start	Invited?	Item
1:30 PM		D2-1-3 Development of Diamond-Like Carbon Coated Electrodes for Corrosion Sensor Applications at High Temperatures K.T. Chiang, L. Yang, R. Wei, K. Coulter (Southwest Research Institute) The coupled multielectrode array sensors have been used as online and real-time monitors for localized corrosion in both laboratory and field systems. Multiple miniature electrodes made of materials identical to the engineering component are used as sensing electrodes. However, these devices have an upper operating temperature limit of approximately 70°C because crevice formation between the electrode and the mounting material. In this paper, a crevice-free electrochemical sensor for corrosion monitoring at temperatures above 100°C is presented. A diamond-like carbon thin film was deposited on the sensing electrodes using a plasma immersion ion deposition process. The diamond-like carbon coating properties were characterized by scanning electron microscopy, transmission electron microscopy and laser Raman spectroscopy. The effectiveness of the diamond-like carbon film in protecting the Alloy 22 (Ni-22Cr-13Mo-3Fe-3W) electrodes in an corrosive NaCl-NaNO₃-KNO₃ salt mixture was demonstrated at 150°C. The average localized corrosion rate measured from the probe with coated electrodes in the NaCl-NaNO₃-KNO₃ salt mixture at 150°C was approximately 0.43 µm/yr. In contrast, the average corrosion rate measured using uncoated Alloy 22 electrodes was approximately two orders magnitude higher than that measured from the probe with coated electrodes. The effective corrosion monitoring capability of the new electrochemical sensor at high temperatures was attributed to the pinhole-free microstructure, high electrical impedance, and high corrosion resistance properties of the diamond-like carbon film.
1:50 PM		D2-1-4 Thermal Stability of UBM Sputtered DLC Coatings With Various Hydrogen Contents H. Ito, K. Yamamoto (Kobe Steel, Ltd., Japan); M. Masuko (Tokyo Institute of Technology, Japan) DLC coatings are used for various sliding members. However, such members used in automobiles, may be exposed to high temperature under insufficient lubrication conditions. Regarding thermal stability of DLC coatings, transition to graphitic structure is suggested in some papers. However, no much work has been done to investigate the effect of hydrogen content on thermal stability. In this study, thermal stability of DLC coatings with various hydrogen contents is reported. DLC coatings were deposited by UBM sputtering. Samples used for thermal stability test were coated with three different hydrogen contents: 1, 10 and 20 at%. Thermal treatment of DLC coatings was conducted in vacuum up to 600°C. In the case of hydrogen content of about 20 at%, results indicated that the hardness of as-deposited film is 25 GPa, after thermal treatment between 100 to 40°C, hardness was nearly constant around 23 GPa. However, it drastically decreased down to 12 GPa after the annealing at 600°C. Raman scattering spectroscopy was carried out to observe the change of micro-structure of DLC. As-deposited samples show broad peaks of G and D band around 1500cm-1, after annealing at 600°C, splitting of D and G band peaks occurred, suggesting a structural change of DLC film to graphitic one. Ball on disk type sliding tests with dry condition was carried out for various DLC films. The wear amount of film after annealing at 600°C was increased drastically, corresponding to the structural change induced by annealing. Also change in structure and tribological property by annealing will be reported by using DLC coatings with variable hydrogen contents.
2:10 PM		D2-1-5 Preparation of Superhard ta-C Films With Low Internal Stress by Means of Excimer Laser Ablation and Irradiation - Relationships Between Preparation Parameters and Properties S. Weissmantel, G. Reisse, D. Rost, M. Nieher (University of Applied Sciences Mittweida, Germany) Recently, we presented a novel method for the preparation of thick superhard ta-C films with low internal stress¹. The method is a combination of excimer laser ablation for film deposition and excimer laser irradiation of as-deposited sub-layers for the reduction of the high stresses. By applying the laser irradiation process alternating to the deposition process and using proper parameters, the method proved to be efficient for the preparation of stress-free several micrometer thick ta-C films. In this presentation we are going to discuss the optimization of the deposition and irradiation parameters in context with surface roughness. In the second part we will present the mechanical properties of up to 4 µm thick ta-C films prepared by our method on WC-hard metal inserts and various types of steel, emphasizing the relationships between the preparation parameters and the film hardness. It will be shown that excellent adhesion on WC-hard metal and steel can be obtained by using intermediate layers, which are also deposited by excimer laser ablation immediately prior to the ta-C deposition. Optimum film hardness measured by a dynamic indentation method was found to be in the range of 55 to 65 Gpa and the optimum Young´s modulus in the range of 700 - 900 Gpa. The tribological properties and the wear resistance of such ta-C films will also be presented and compared to other hard coatings. Finally, some examples of coated tools will be shown and the industrial potentialities of the method will be discussed. ¹S. Weissmantel, G. Reisse, D. Rost, Surface & Coatings Technology 188-189 (2004) 268.
2:30 PM		D2-1-6 Superhard Low Friction Carbon Coatings Deposited by Combined HIPIMS-Unbalanced Magnetron Sputtering W.-D. Münz, S. Kunkel, M. Schenkel, T. Zufrass (SVS Vacuum Coating Technologies, Germany); J. Winter, N. Bibinov (PAC Plasma Consulting Applications GmbH & Co. KG, Germany); M. Stüber, M. Rinke (Forschungszentrum Karlsruhe, IMF I, Germany); H. Kersten, T. Strunskus (IEAP, University of Kiel, Germany); K. Bewilogua, P. Willich (Fraunhofer IST, Germany) Based on research concerning Me-DLC and C-DLC coatings as well as on adhesion enhancing multilayer intermediate layers carried out at Fraunhofer IST, the C-DLC process has been revised employing a combined HIPIMS unbalanced magnetron sputtering process in an industrial multi-target PVD coater. Introducing the well known WC layer as the intermediate adhesion layer a binder free WC target was used to allow a HIPIMS metal ion pretreatment of the substrates prior to film deposition. Providing sufficiently high pulse energies OES analyses have verified W⁺² and W⁺³ ions in the wavelength range between 200 and 300 nm. The ion bombardment was carried out with an acceleration voltage of typically -1.2 kV. Reducing the bias voltage to -75 V a first WC layer was grown in pure HIPIMS mode. The deposition process was continued by simultaneous HIPIMS and UBM sputtering of WC up to a thickness of 0,5 µm. Carbon deposition took place by UBM sputtering of 99,99 % graphite targets in an argon/acetylene atmosphere. Varying the acetylene flow rate a distinct hardness maximum was found at rather low flow rates as compared to argon with H_Pl values between 40 and 50 GPa and a friction coefficient of F = 0.1. Increasing the acetylene flow further, the hardness decayed to 15 GPa and the friction coefficient reached values as low as F = 0.07 to 0.08. The deposition rate depended strongly on the power dissipated on the graphite targets as well as on the acetylene flow rates (0.8 to 2.5 µm/h). The superhard coating exhibited a hydrogen content of 10 at. %. The hardness of the coatings clearly depend on the bias voltage. Raman analyses of the superhard coatings showed peak intensity ratios of D and G bands typical of amorphous carbon. In addition the ratio of sp²/sp³ which has been measured by NEXAFS changes significantly with the acetylene flow. This observation supports the hypothesis of the incorporation of C-nanoparticles formed in the plasma and embedded into the growing DLC film thus explaining the hardness maximum. First industrial tests of the sandwich layer WC/C-DLC revealed excellent results on drawing tools, medical tools and automotive parts.
3:10 PM		D2-1-8 Structural and Mechanical Properties of DLC Films Deposited by an Anode Layer Source M. Kahn (Joanneum Research Forschungsgesellschaft GmbH, Austria); M. Cekada (Jozef Stefan Institute, Slovenia); R. Berghauser (Joanneum Research Forschungsgesellschaft mbH, Austria); C. Mitterer (University of Leoben, Austria); Ch. Bauer (University of Graz, Austria); W. Waldhauser, E. Brandstaetter (Joanneum Research Forschungsgesellschaft mbH, Austria) In sensor technology and for medical implants highly defect free DLC coatings are mandatory. The paper presents newest data from the chemical and mechanical investigation of high quality diamond-like carbon films deposited by an anode layer source. An anode layer source is a special type of an ion gun, which can be fed with carbon precursors like acetylene to deposit such highly defect free diamond-like carbon at room temperature. The study focuses on the influence of the process parameters like discharge voltage in the anode layer source, process pressure and acetylene flow on the properties of the deposited films. Films were deposited onto unmoved, rotated and oscillated substrates. The structure of the films was investigated by Raman spectroscopy and the mechanical properties were investigated by nanoindentation. The residual stresses in the films were determined by employing the curvature method. The main Raman bands of the diamond-like carbon films show a correlation of the peak position, intensity and full width at half maximum to the deposition parameters. In general, the films are becoming higher in sp³ content while lowering the voltage applied to the anode layer source in the investigated area from 3 kV to 1 kV. The chemical homogeneity was characterised by automated Raman mappings. Moreover, the Raman band parameters were correlated with hardness, stress and young’s modulus.
3:30 PM		D2-1-9 Aging Behavior of the Plasma Treated Si-Incoporated Diamond-Like Carbon Surface J.W. Yi (Korea Institute of Science and Technology, Korea); H.R. Kim (Ewha Womans University, Korea); M.W. Moon (Korea Institure of Science and Technology, Korea); J.-K. Kim (Korea Institute of Materials Science, Korea); K.-R. Lee (Korea Institute of Science and Technology, Korea) We have investigated the aging effect of O₂2 and N₂ plasma treatment on a pure DLC and Si-DLC (2% Si incorporated) surfaces by measuring wetting angle of a water droplet. The pure DLC and Si-DLC films deposited on Si(100) substrate using rf-PACVD technique [1] were treated with N₂ and O₂ plasma with bias voltage at -400V for 10 min in rf-PACVD chamber. Upon exposing films to ambient air conditions, wetting angle were measured with time upto 30 days. Each wetting angle was measured on three different locations and a droplet of 5 micro-liter in volume was blown off the surface with nitrogen following the measurement. In case of N₂ plasma treatment, wetting angle for the as-treated pure DLC and Si-DLC surface was measured of 10° as-treated, then reached the steady state angle of 60° after 10 days. However in case of O₂ plasma treatment on pure DLC, initial wetting angle was measured less than 5°, then increased gradually upto 50° after 10 days, implying that recovery rate on N₂ treated pure DLC films were found to be much faster than that on O₂ treated surfaces. However, O₂ treated Si-DLC was maintained as less than 15° even after 30 days, indicating a permanent hydrophilic surface. In order to examine the aging phenomena of wetting angle, surface bonding characteristics were performed with XPS analysis. The pure DLC and Si-DLC films as-treated and aged by 20 days were compared for structural changes in atomic bondings at the activated surfaces. Furthermore surface morphologies of films were explored using AFM for analysis of permanent wetting angles at steady state after N₂ and O₂ treatment.
3:50 PM		D2-1-10 Electrical Properties Within 70-300 K Of Boron Containing Diamond-Like Carbon Films Deposited By Femtosecond Pulsed Laser Ablation C. Donnet, A. Sikora (University Jean Monnet, France); A. Berkesse, O. Bourgeois, J.L. Garden (Institut Néel UPR CNRS 2940, France); C. Guerret-Piécourt (Ecole Centrale de Lyon, France); A.S. Loir, F. Garrelie (University Jean Monnet, France) We have studied the electrical properties of pure diamond-like carbon (DLC) and boron-doped DLC thin films grown on sapphire substrates by femtosecond pulsed laser deposition. The amorphous DLC films, containing a majority of sp³ bonds, have been deposited at room temperature by ablating graphite targets with an amplified Ti:sapphire laser of 800 nm wavelength and a pulsed duration of 150 fs in high vacuum conditions. Doping with boron has been performed by ablating alternatively graphite and boron targets with the femtosecond laser. The morphology of these films at the microscopic scale has been examined by Atomic Force Microscopy (AFM) and Scanning Electron Microscopy equipped with a field emission gun (SEM-FEG). Raman spectroscopy has been also used to characterize the structural disorder in the films. Two types of films have been studied: films of pure DLC and boron-doped films with different percentage of doping in the 2-8% range. A regular electrical four probe technique was used to measure the resistance. The typical resistivity ranges between 100 Ohm.cm for pure DLC down to few Ohm.cm for highest doped DLC at RT. The electrical resistivity of these films has been characterized in the temperature range of 70 K to 300 K. The global behaviour of the resistance is an exponential decrease with increasing temperature. A theoretical model is proposed to explain this temperature dependence of the resistance, where the electrical conductivity of DLC is assumed to be due to hopping. For doping by metallic elements, it was observed that the resistivity decreases. The addition of dopant may change the proportion of sp³ and sp² bonds which could play a significant role in electrical properties of the DLC films. The measured temperature coefficients of resistance (TCR), which represent the sensibility of the thermometer, are as high as 3.85% for pure DLC films. TCRs decrease when the doping increases. The deposition parameters are optimized in order to get the best performances: the higher temperature coefficient of resistance, up to 300 K and the lower resistivity. The high value of TCR measured for pure DLC will allow its use as a thermometer element in micro and nanodevices at room temperature.
4:10 PM		D2-1-11 Formation of Nano-Columnar Amorphous Carbon Films via Electron Beam Irradiation and their Mechanical Characterization T.A. Aizawa (Osaka Prefecture University, Japan); E.I. Iwamura (Arakawa Chemicals Co. Ltd., Japan); T. Uematsu (Tokyo Metropolitan Institute of Research for Industry, Japan) Hard mono-layered carbon-origin coatings have been successfully applied to cutting tools, forming dies and various mechanical parts. In particular, DLC (diamond-like carbon) is widely used in market from protective coating of rotating discs to wear-resistant coating of automotive parts. Their mechanical behavior is mainly described by hardness; e.g. ratio of sp³ to sp² has been traditionally discussed to control their hardness. Authors have been concerned with the controllability of mechanical behavior by nano-structuring the coating. It was found that the naturally grown amorphous carbon film should be modified to have a nano-columnar structure via the electron beam (EB) irradiation. High-resolution TEM as well as Raman-spectroscopy, has become a tool to describe the formation of nano-columnar structure via EB-irradiation. In the present paper, nano-indentation tests are fully utilized to describe the variation of mechanical responses with increasing the duration time in EB-irradiation. Without EB-irradiation, a load-displacement curve during loading and unloading has a typical hysteresis due to nonlinear deformation inside coating. In case of EN-irradiation for 300 s, this hysteresis is much reduced so that load-displacement curve becomes reversible. This change in mechanical behavior corresponds to regularization of microstructure in Raman spectroscopy as well as formation of fine microstructure in the observation via the in-lens SEM observation. Through regularization via electron beam irradiation, nano-columnar composite of graphite-cluster intercolumnar network in the original amorphous carbon coating is formed to change its mechanical response. Finite element method is further utilized to explain the reversible deformation in nano-indentation for the nano-composite coating.
4:30 PM		D2-1-12 Hemocompatibility of Plasma Treated Si Incorporated Diamond-Like Carbon Films R.K. Roy, M.W. Moon, K.-R. Lee, D.K. Han (Korea Institute of Science and Technology, Korea); J.-H. Shin (Asan Hospital, Korea); T. Hasebe (Tachikawa Hospital, Japan); A. Kamijo (University of Tokyo Hospital, Japan) We investigated the effect of surface modification on the hemocompatibility in Si incorporated hydrogenated amorphous carbon (a-C:H) films prepared by r.f. PACVD method. Si incorporated diamond like carbon films (Si-DLC) were prepared using benzene and diluted silane (SiH₄/H₂ = 10:90) as the precursor gases. The Si-DLC films were then subjected to plasma treatment using various gases like N₂, O₂, H₂ and CF₄. The plasma treated Si-DLC films showed a wide range of water contact angles from 13.4° to 92.1°. A hydrophilic surface was obtained for O₂ plasma treated Si-DLC films while CF₄ plasma treatment gives rise to a hydrophobic surface. The blood plasma protein adsorption tests showed higher albumin adsorption for O₂, N₂ and CF₄ plasma treated Si-DLC films while minimum fibrinogen adsorption was observed in case of H₂ plasma treated Si-DLC films. A higher aPTT was noted in case of O₂ plasma treated Si-DLC films. The high albumin to fibrinogen ratio seemed to explain the improved hemocompatibility of the O₂ plasma treated Si-DLC films. The O₂ plasma treated Si-DLC films also minimized platelet adhesion and activation compared to other samples. The O₂ plasma treated Si-DLC films can be a suitable coating material for endovascular SMART nitinol stents. We found that C-O bonds on the surface play a significant role in improving the hemocompatibility.