Papers

ICMCTF2005 Session D2-3: Diamond-Like Carbon and Diamond Materials

Friday, May 6, 2005 8:30 AM in Room Royal Palm 1-3

Friday Morning

Start	Invited?	Item
8:30 AM		D2-3-1 The Reduced Residual Compressive Stress of Si Incorporated ta-C Films : Molecular Dynamics Study S-.H. Lee, S.-C Lee (Korea Institute of Science and Technology, South Korea); Y.-C. Chung (Hanyang University, South Korea); K.-R. Lee (Korea Institute of Science and Technology, South Korea) There have been remarkable interests in the structures and properties of tetrahedral amorphous carbon (ta-C) films owing to their superior chemical and physical properties. However, high residual compressive stress of ta-C film results in the delamination of the films from the substrate. Many studies have been thus focused on the reduction of the residual stress. Recently, it was reported that a small amount of Si addition to ta-C films could significantly reduce the residual stress with a little degradation of the mechanical properties [1]. In order to understand the role of Si atoms in the ta-C film structure, we investigated the deposition behaviors of highly energetic carbon and silicon atoms on a diamond (100) substrate by using a molecular dynamic simulation. Brenner and Tersoff potentials were used for C-C and C-Si interactions, respectively. The film depositions were simulated at a kinetic energy of 75 eV for the Si concentration ranging from 0.5 % to 20 %. We examine the structure and properties such as atomic bond configuration, radial distribution, average density, average residual stress and elastic modulus. The MD simulation reproduced the experimental observations [1]. The mechanism and the role of the incorporated Si will be addressed in terms of the atomic bond structure near the incorporated Si atom. [1] Churl Seung Lee, Kwang-Ryeol Lee, Kwang Yong Eun, Ki Hyun Yoon and Jun Hee Han, Diam. Rel. Mater., 11, 198-203 (2002).
8:50 AM		D2-3-2 Nanocomposite Metal-Carbon Based Films Deposited by Femtosecond Pulsed Laser Ablation N. Benchikh, F. Garrelie, C. Donnet (University Jean Monnet, France); C. Wolski, R.Y. Fillit (Ecole Nationale Superieure des Mines, France); F. Rogemond, J.L. Subtil (University Jean Monnet, France) Nanostructured coatings of metal containing diamond-like carbon have been prepared by femtosecond pulsed laser deposition (PLD). The films have been deposited by ablating sequentially graphite and metallic targets under vacuum conditions with an amplified Ti:sapphire laser. Nickel or tantalum have been co-deposited with carbon at concentrations in the range of 2 – 15 at.%. The objective was to characterize the a-C:Ni and a-C:Ta film compositions and nanostructures, considering the opposite chemical affinity of both metallic elements in respect to carbon. The films have been investigated by Rutherford backscattering spectrocopy, X-ray photoelectron spectroscopy, grazing angle X-ray diffraction, electron energy loss imaging, scanning and high resolution transmission electron microscopies. Evidence of nanometer sized particles embedded in the carbonaceous matrix is shown. Metallic and carbide inclusions have been identified respectively with Ni and Ta co-ablation. The ability of femtosecond pulsed laser deposition to deposit nanocomposites carbon based films and to control their nanostructure is discussed.
9:10 AM		D2-3-3 Silicon Induced Changes in the Microstructure and Nano-Mechanical Properties of Hydrogenated Amorphous Carbon Films Prepared by PECVD A.A. Ogwu (University of Paisley, United Kingdom); B. Beake (Micro-Materials, Ltd., United Kingdom); D. Haddow (Thales Optronics Ltd, Glasgow, United Kingdom); T. Okpalugo, P. Maguire, J.A. McLaughlin (University of Ulster, Northern Ireland, United Kingdom) The reliability of MEMS devices fabricated from a-C:H(DLC)and other films, recently reported in the literature, will depend on the mechanical and physical properties of the thin films used for their fabrication. Visible wavelength Raman spectroscopy at 514.3nm has been used to investigate the structural network modification induced by silicon addition to hydrogenated amorphous carbon thin films during deposition by the plasma enhanced chemical vapour deposition (PECVD)process.The changes induced in the nano-mechanical properties of the films by silicon addition was also monitored by nano-indentation and nano-impact testing. Our investigation has revealed that although silicon addition will reduce stiction in the films, through changes in the surface chemical bonds, beneficial for MEMS applications, it can have a deleterious effect on their mechanical properties if not added optimally.
9:30 AM		D2-3-4 Effects of Sulfur Addition to CH_x Films C.A. Freyman, Y.W. Chung (Northwestern University) Amorphous hydrogenated carbon films (CH_x) have shown ultra low friction coefficients (µ<0.01) in dry nitrogen testing environments. The ultra low friction properties degrade with the addition of water vapor to the testing environment. In this work, we explore the effects of sulfur addition to magnetron sputtered a-C:H films on elastic modulus, hardness and tribological properties as a function of relative humidity in the testing environment. Film microstructure and chemical state of sulfur have been investigated with transmission electron microscopy, electron energy loss spectroscopy, x-ray photoelectron spectroscopy, auger electron spectroscopy. Hydrophobicity of these films was obtained via contact angle measurements. These studies show that with appropriate control of the film-substrate interface, sulfur addition of a few atomic percent is sufficient to reduce the adverse effect of humidity on friction.
9:50 AM		D2-3-5 Three Dimensional Film Coating of Hydrogenated Amorphous Carbon Y.K. Koga, O.T. Tsuda, M. Ishihara (AIST, Japan); Y. Setsuhara (Osaka University, Japan) Three dimensional plasma CVD system of hydrogenerated amorphous carbon film coating has been developed. By a high density volumetric plasma source system equipped with multiple low inductance antenna, the thickness of films on the hexagonal substrate holder was obtained with 4 percent uniformity. The films are durable for the tribology test with a high load of 20 N up to more than 20000 cycles, showing the low specific wear rate and the friction coefficient of 0.04.
10:10 AM		D2-3-7 Gas Permeation Through Polymer Membranes Modified by a-C:H(N) Films Deposited using Butene, Butadiene and Nitrogen Gas Mixture R.A. Simao, C.A. Achete, E. Castro Vidaurre, C. Habert (Coppe - UFRJ, Brazil) Pure amourphous hydrogenated carbon (a-C:H) and amorphous nitrogen incorporated (a-C:H(N)) films, with thickness up to 1 µm, were deposited onto asymmetric porous substrates of polysulfone (PSf) membranes by 13.56 MHz r. f. self bias glow discharge using pure Butadiene, Butene or mixtures with nitrogen. Several deposition parameters, namely bias voltage (V_b) , nitrogen partial pressure (P_N) and total pressure P, were varied in a controlled way. The permeation of the gases N₂, and CO₂ was measured and the reduction of the permeability coefficient was correlated to composition and structure of the a-C:H(N) films obtained with different gases. The stoichiometry of the layers was analyzed using ion-beam techniques on films deposited onto silicon samples. The surfaces were analyzed using optical microscopy and atomic force microscopy (AFM). Room temperature conventional gas permeation measurements were performed on uncovered membranes and as a function of film thickness for layers deposited with different gases, (V_b) and (P_N). It was observed a general tendency of reduction of the permeability coefficient with the film thickness, reaching a minimum reduction of 95% for polymerlike layers of about 100 nm. Surprisingly, the barrier efficacy of the coating decreases with increasing a-C:H(N) film thickness or increasing bias voltage. This unexpected result is attributed to both, appearance of a network of cracks on the hole surface of the coating and the severe etching of the membrane surface during the deposition.
10:30 AM		D2-3-8 Comparative Study Of Amorphous Hydrogenated Carbon Films Produced from Methane, Butane, Butadiene C.A. Achete, P.J.G. Arajo, R.A. Simao (Coppe - UFRJ, Brazil); C.M. Lepienski (Catholic University of Parana, Brazil) Amorphous hydrogenated carbon (a-C:H) films and its alloys are being successfully used opptical filters, protective layers semiconductors and also as a barrier against permeation and in polymers superficial modification in order to produce liquid-gas separation membranes. However, the residual stress is still a serious problem to be solved to improve the quality of the system. In the present work a-C:H were produced by glow discharge at the radio frequency of 13,56MHz using the following gases: Methane, Butane, Butadiene. This technology can be used with membranes, polymers surfaces, mechanical tools, surfaces needing protective coatings such as fibers and optical "things". Different self-bias were used in order to investigate its influence on the produced films. Pieces of silicon (100) were used as substrate. The nano hardness was measured by nano identation technique and related to the applied self-bias. Films that present high values of residual stress can have cracks. Different values for the residual stress, nano-hardness were obtained by changing the work gas. The a-C:H films thermal stability was measured by the gas effusion technique. The nano-structure of the films as its frictional coefficient was analyzed by he atomic force microscopy (AFM).
10:50 AM		D2-3-9 Modification of Atomic Bond Structure of Tetrahedral Amorphous Carbon by Ar Background Gas in Filtered Vacuum Arc Process T.-Y. Kim, S-.H. Lee (Korea Institute of Science and Technology, South Korea); C.S. Lee (Korea Electronics Technology Institute, South Korea); K.-R. Lee (Korea Institute of Science and Technology, South Korea); J.-H. Han (Korea Research Institute of Standard and Science, South Korea); K.H. Oh (Seoul National University, South Korea) The properties and atomic bond structure of tetrahedral amorphous carbon (ta-C) films deposited by filtered vacuum arc process with Ar background gas, was investigated. Even if no Ar atoms are incorporated in the ta-C films as observed by Rutherford backscattering spectrometry, atomic bond structure and the properties were sensitive to the Ar flow rate. As the Ar flow rate increased, defect density of the film measured by electron spin resonance (ESR) was significantly decreased whereas the sp²/sp³ fraction of the films characterized by Raman spectroscopy was not varied. The residual compressive stress of the film decreased by about 35% with increasing the Ar flow rate. On the other hand, the sheet resistance of the film increased as the Ar flow rate increased. This phenomenon could be explained by the relaxation of the atomic bond distortion in the films resulting in the reduction of the unpaired π electrons. Molecular dynamic simulation of ta-C film deposition showed that this phenomenon is closely related to the energy dispersion of the carbon ions due to the Ar background gas.