Papers

ICMCTF2001 Session D2-1: Synthesis and Characterization of Diamond and Carbon-based Materials

Wednesday, May 2, 2001 8:30 AM in Room Royal Palm 4-6

Wednesday Morning

Start	Invited?	Item
8:30 AM		D2-1-1 Growth, Characterization and Mechanical Properties of Nanodiamond Films Deposited from Ar/CH4 Microwave Plasma C.T. Wu, K.H. Chen (Institute of Atomic & Molecular Sciences Academic Sinica, Taiwan); L.C. Chen (National Taiwan University, Taiwan); G. Lehmann, P. Hess (University of Heidelberg, Germany) The use of Ar/CH4 plasma has been effective for producing phase-pure nanodiamond films independent of film thickness [1]. In the present report, nanodiamond films were deposited by microwave plasma enhanced chemical vapor deposition from Ar/CH4 gas mixtures with and without H2. The addition of a minute amount of H2 greatly improves the stability of the microwave plasma, therefore, helps sustaining growth of very thick nanodiamond films. The effects of microwave power, chamber pressure, source gas composition, growth temperature and biasing during growth on the growth rate and grain size of the nanodiamonds have been investigated. It is observed that the higher the microwave power and gas pressure the higher the growth rate. Furthermore, the grain size of the nanodiamond films was strongly affected by the hydrogen gas flow rate and the substrate temperature. The uniformity and the grain size of the nanodiamond films were confirmed by high-resolution transmission electron microscopy from both plain view and cross-section view. Finally, the elastic constant and hardness of the nanodiamond films were characterized using surface acoustic wave spectroscopy. [1] D. Zhou, T. G. McCauley, L. C. Qin, A. R. Krauss and D. M. Gruen, J. Appl. Phys. 83, 540 (1998).
8:50 AM		D2-1-2 Gas-Phase and Plasma-Surface Reactions in Radiofrequency Discharges of C₂H₂-N₂-Noble Gas Mixtures M.A. Bica de Moraes, S.F. Durrant, F.P. Rouxinol (Universidade Estadual de Campinas, Brazil) Actinometric optical emission spectroscopy was used to investigate the reaction mechanisms occurring in radiofrequency discharges of C₂H₂-N₂-noble gas mixtures used to deposit amorphous nitrogenated carbon films. The noble gases employed were He, Ne, Ar and Kr. Both gas phase and surface reactions were investigated. The formation of the CH and CN species, probably two precursors of film growth, was studied as a function of the N₂ to C₂H₂ and noble gas to C₂H₂ flow ratios. Nitrogen strongly enhances the formation of CH due to gas phase reactions between atomic nitrogen and C₂H₂ or other carbon-containing species. The CH concentration also depends on the flow rate and nature of the noble gas, being particularly sensitive to He. As expected, the CN concentration increases with increasing N₂ to C₂H₂ flow ratio. However, a relatively high CN concentration could be observed even in discharges without nitrogen so long as a nitrogen-containing carbon film was previously formed on the walls of the vacuum chamber. The CN species were then attributed to surface reactions between the plasma and the film. Using a transient actinometric mode [S.F. Durrant et al., J.Vac. Sci. Technol. B, 13 (1995) 1901] the formation of CN by plasma-surface interactions was investigated in discharges of individual noble gases. The results strongly indicate that the emission of the CN species is due to metastable noble gas atoms which release their energy upon collisions with the film surface, breaking the carbon bond linking nitrile groups to other carbon atoms in the films surface.
9:10 AM		D2-1-3 Nitrogen-Doped Plasma Enhanced CVD Amorphous Carbon: Processes and Properties S.M. Smith, S.A. Voight, H.G. Tompkins, A. Hooper, A.A. Talin (Motorola, Inc.) In this work we discuss thin film amorphous carbon which is deposited in a dual frequency plasma enhanced CVD system with a nitrogen-containing ambient. Unlike most carbon films deposited using PECVD, the films in this study were deposited on the grounded electrode and therefore subject to little energetic bombardment during growth. Methane was used as the carbon-containing precursor. We illustrate some potential applications for this type of film and discuss the effect of various process parameters on resulting film properties, such as optical constants, stoichiometry, and chemical bonding and structure.
9:30 AM		D2-1-4 Technological Maps for ta-C Deposition by Subplantation Modelling B. Schultrich (Fraunhofer Institute for Materials and Beam Technology, Germany); N. Rackwitz (Fraunhofer Institute for Material and Beam Technology, Germany) The extremely broad structural variability of carbon films is based on the competition of trigonal sp² bonds leading to layered structures (as in graphite)and tetrahedral sp³ bonds leading to three-dimensional networks (as in diamond). These complementary structures may be combined in amorphous carbon films as they are produced by highly activated ion or plasma beams. Amorphous films with up to 80 % diamond bonds and corresponding hardness has been realized in this way. The necessary deposition conditions are qualitatively well known: high particle energy, low deposition temperature, not too grazing incidence. For quantitative estimation of the various technological parameters (including ion flux density and thermal transport) a model for the film formation has been developed. It is based on the subplantation of energetic particles into the surface layer, on the formation of pressure gradients by these interstitials, on the pressure-driven and temperature-determined relaxation. The different factors may be summarized in a subplantation parameter S describing the ratio of film growth rate to drift velocity. In this way it is possible to determine the carbon structure (characterized by the density or the corresponding sp² : sp³ ratio) in the multidimensional space of particle energy (and their distribution), substrate temperature, ion flux density and angle of incidence (i.e. geometry and position). From these technological maps characteristic tendencies are extracted and discussed in comparison with experimental results. The application of the simulation for optimization of the industrial Laser-Arc deposition of superhard amorphous carbon films is demonstrated.
9:50 AM		D2-1-5 Strucutre and Properties of Si Incoporated Tetrahedral Amorphous Carbon Films Prepared by Hybrid Filtered Vacuum Arc Process C.-S. Lee (Korea Institute of Science and Technology and Yonsei University, Korea); K.-R. Lee (Korea Institute of Science and Technology, KOREA); K.Y. Eun (Korea Institute of Science and Technology); K.-H. Yoon (Yonsei University, Korea) Because of high hardness and high fraction of sp³ hybridized atomic bonds, tetrahedral amorphous carbon (ta-C) film has attracted much attention. However, high residual compressive stress results in poor adhesion on various substrates and ambiguity in structure analysis by Raman spectroscopy. In addition to substrate biasing method, third element addition can be a promising method to control the residual stress and atomic bond structure. In the present work, ta-C film was prepared by filtered vacuum arc (FVA) of graphite without substrate biasing. Si was incorporated in the ta-C film by simultaneous magnetron sputtering of Si during the film deposition. Si concentration in the film could be varied from 0 to 75 at.% by increasing Ar gas flow to the sputter source. The residual compressive stress of ta-C film was strongly dependent on the Si concentration. Small amount of Si less than 1 at.% could reduce the residual compressive stress by 30% (from 7GPa at 0 at.% of Si to 5 GPa at 1 at.% of Si). When the Si concentration was larger than 20%, the residual stress decreased to less than 1 GPa when Si concentration was 75 at.%. The effect of Si on atomic bond structure and properties will be discussed based on the Raman, XPS and FTIR spectrum analysis. Tribological behavior of Si incorporated ta-C film will be also presented.
10:10 AM		D2-1-6 Dual Plasma Hot-Filament and Hollow Cathode CVD Technique of Diamond Growth A. Kromka, J. Jan, V. Malcher, V. Dubravcova (Slovak University of Technology, Slovakia) The influence of dual-plasma reactor arrangement on possible lowering of substrate temperature is presented. In such a hybrid design, the gas mixture consisting of methane and hydrogen is decomposed by dc plasma formed either over the hot filaments or over the hot hollow cathode plate, respectively. Diamond films have been grown on (100) silicon substrates in two basic reactor modifications, in the dual-plasma assisted HF CVD and in hybrid hollow-cathode CVD arrangement. The influence of process conditions and reactor design on the growth of diamond thin films is investigated independly on incubation and nucleation effects. Polycrystalline diamond films are characterized by Raman spectroscopy, scanning electron microscopy and X-ray diffraction measurements. The obtained results indicate and enhancement of gas decomposition in the hybrid hollow cathode arrangement where the substrate bombardment by electrons is five times higher than that one for the dual plasma HF CVD arrangement. Furthermore, a possible lowering of substrate temperature and activation energy of diamond growth process is discussed.
10:30 AM		D2-1-7 Nanostructured, Nitrogen Doped, Carbon Materials for Hydrogen Storage A. Badzian, T. Badzian, E. Breval, A. Piotrowski (The Pennsylvania State University) Astonishing feature of carbon materials is a variety of morphological forms created by growth processes. We report herein that a growth process originated from CVD diamond synthesis. Addition of nitrogen gas to the microwave plasma ignited in a CH4/H2 mixture has a profound influence on the crystal structure and morphology of diamond and graphite formed in this process. Diamond appears as nanocrystalline material with a high degree of disorder in stacking of tetrahedra. Graphite exists in several forms: single crystal net-like planar form, nanoparticulates, nanotubes with perpendicularly stacked graphite rings. Nitrogen incorporation into these forms is about 1at%. Nanotubes are also formed in the process of etching graphite by nitrogen plasma. Nanotubes and particulates are built from structural units, which are graphite nanocrystals with dimensions as small as 2.5 x 2.5nm. Self-assembling tendency of these units' results in different forms looking like built from bricks. They are as f ollows: rings 70nm in diameter, nanotubes 60nm in diameter or flat particles 25nm in diameter. This material contains few atomic%N. Electron diffraction indicates on lattice expansion of graphitic C-N nanocrystals comparing to pure graphite. C r eation of active sites for hydrogen molecule adsorption by incorporation of nitrogen atoms to the graphitic network is a subject of speculation. Hydrogen intake in materials grown from the C-H-N gas system is low in the range of 1wt%. The measurements have been performed using thermogravimetric method. TGA-150 Cahn microbalance measurements were corrected to the buoyancy effect.
10:50 AM		D2-1-8 High Quality Diamond Materials by Chemical Vapor Deposition J.E. Butler (Naval Research Laboratory) The growth of diamond materials spans a continuum of quality, grain sizes, and defect related properties, from materials exceeding the best quality natural diamonds to materials with so many defects as to be barely recognizable as crystalline diamond. In this presentation, I shall focus on the growth of high quality diamond materials, both polycrystalline and single crystal layers.
11:30 AM		D2-1-10 Effects of rf Power Burst Modulation of Magnetron Sputtering on the Properties of Amorphous Carbon Films J.L. Andjar, F.J. Pino, M.C. Polo, E. Bertran (Universitat de Barcelona, Spain) Thin films of amorphous carbon (a-C) were deposited on silicon and glass substrates by magnetron sputtering of a graphite target in an Ar atmosphere. The rf power (13.56 MHz) supplied to magnetron cathode was burst-modulated in order to study the effects of pulsed magnetron sputtering on the a-C growth. The main parameters of the pulsed rf sputtering process were: the peak power level, the sputtering-on time (dwell time) and the pulse modulation frequency. In addition, the energy of incident ions to the growing a-C surface was varied by applying a negatively bias voltage to the substrate. The structural and mechanical film properties were studied by Raman spectroscopy, transmission electron spectroscopy, and by performing stress, friction and wear measurements, respectively. The results were discussed in terms of the effects of pulsed magnetron sputtering parameters on the growth of a-C films to be used as hard protective coatings.