ICMCTF1998 Session D2-2: Synthesis and Characterization of Diamond and Related Materials (2)

Tuesday, April 28, 1998 1:30 PM in Room Forum/Senate/Committee

Tuesday Afternoon

Start	Invited?	Item
1:30 PM		D2-2-1 Deposition Rate Effects on the Properties of Highly Tetrahedral Amorphous Carbon (ta-C). M. Chhowalla, G.A.J. Amaratunga (University of Liverpool, United Kingdom) Tetrahedral amorphous carbon (ta-C) with sp³ diamond like fraction upto 80% can be deposited using numerous deposition techniques. The sp³ bonding in ta-C is promoted by the shallow implantation (subplantation) of energetic carbon species into the surface of the growing film. Ion energy and substrate temperature have been shown to be critical parameters for deposition of highly ta-C. In this study, using a filtered cathodic vacuum arc plasma, we report on the importance of deposition rate as an additional factor which may partially account for the observed differences in the optimum energy. We have found that an increase in the ion flux (i.e. deposition rate) leads to a decrease in the optimum ion energy. We argue that the shift in the optimum ion energy can be attributed to the surface heating effects due to ion bombardment. We correlate our data to a model which takes into account thermal effects of deposition rate.
1:50 PM		D2-2-2 Development of Adherent Diamond Coatings on Titanium Alloy J.R. Vijayen, V.K. Sarin (Boston University) The titanium alloy, Ti-6%Al-4%V, has many attractive properties including a high elastic modulus, relatively low density, and high specific strength. Such properties have resulted in its widespread use in the aerospace and biomedical industry. It is projected that enhancing the wear resistance of these alloys could further extend their engineering applications. It has been reported that substantial improvements in tribological performance can be realized through deposition of a thin diamond coating. However, the adhesion characteristics of such coatings on Ti-6%Al-4%V alloys are poor. This is primarily due to differences in thermal expansion coefficients between the diamond and titanium alloy which generates high stresses at the coating/substrate interface. The oxy-acetylene combustion flame technique was employed to assist in the development of adherent diamond coatings on Ti-6%Al-4%V alloy. The effect of fundamental process parameters such as substrate temperature, inlet gas stoichiometry, and substrate position in the flame on nucleation and growth rate, morphology, and coating adhesion were quantitatively and qualitatively evaluated. Process parameters were optimized to yield high quality, continuous diamond coatings on the titanium alloy substrates. The coatings were characterized using Scanning Electron Microscopy (SEM) and X-Ray Diffraction (XRD). The adhesion was evaluated by indentation and macroscratching testing techniques.
2:10 PM		D2-2-3 Fracture Strength in High Temperature of Free Standing CVD Diamond Films Y.K. Kishi, Z.Y. Yajima, K.S. Shimizu (Kanazawa Institute of Technology, Japan); S.T. Takeuchi, M.M. Murakawa (Nippon Institute of Technology, Japan) The mechanical properties of CVD diamond films must be known as quantitatively as possible in order to render them to be usable for various industrial parts. In regard of this several investigators have measured the properties in question, but their results including, for example, those on Young's modulus and fracture strength have been inadequate particularly from the view point of clarifying the effect of the thickness and test temperature. In this paper, the above-mentioned properties to be the most fundamental mechanical ones were evaluated. Three points bendig test conducted under R.T.-1073K have been employed for investigating the relationship between stress - strain curves and thickness of free standing diamond films. The effects of film thickness and test temperature on Young's modulus and fracture strength of the films were discussed on the basis of these experimental results.
2:50 PM		D2-2-5 The Investigation of Thermal Effect on the Properties of Pulsed Laser Deposited Diamond-like Carbon Films H.H. Park, H.S. Jung, S.Y. Lee, Y.S. Jung (Yonsei University, KOREA) Diamond-like carbon(DLC) films have excellent properties for wide range of high technology applications but the relation between growth mechanism and properties of the films was not well known. The purpose of this study is to find the factor which affects the properties of DLC films.We have grown thin carbon films by pulsed laser deposition and investigated the extent to which the properties of such film are substrate dependent. As received or surface cleaned Si(100) and Si(111) wafers were used to investigate the effects of surface orientation and native oxide on the formation of DLC. Films were grown by ablating material from graphite target. The substrate temperature was 20°C and the power density was 12 J/cm². The effects of variation in these parameters were also examined but it was revealed that the above condition was optimal one for the preparation of DLC. The distance between target and substrate was kept as 3cm. The properties of DLC films were characterized by various techniques. The surface morphology and bonding structure of DLC films were analyzed by scanning electron microscope, atomic force microscopy and Raman spectroscopy. The chemical state of the films was also investigated by x-ray photoelectron spectroscopy and in-depth analysis was done by angle-resolved x-ray photoelectron spectroscopy. These various characterization techniques confirm that there is a correlation between substrate condition and the degree of diamondlike qualities.
3:10 PM		D2-2-6 Thermal Diffusion in MD Simulations of Thin Film Diamond Deposition B.A. Palithorpe, D. Mitchell (University of Sydney, Australia) Molecular Dynamics simulations of carbon atom depositions are used to investigate energy diffusion from the impact zone. A modified Stillinger-Weber potential models the carbon interactions for both sp2 and sp3 bonding. Simulations were performed of 50 eV carbon atom depositions onto the (111) surface of a 3.8nm x 3.4 nm x 1.0 nm diamond slab containing 2816 atoms in 11 layers of 256 atoms each. The bottom layer was thermostated to 300K. At every 500-th simulation time step (27fSec), the average local kinetic energy, and hence local temperature, is calculated. To do this the substrate is divided into a set of 15 concentric hemispherical zones, each of thickness one atomic diameter (0.14nm) and centered on the impact point. Aside from the central zone, each shell contains at least 5-10 atoms, with outer shells containing more atoms.
3:30 PM		D2-2-7 On the Hardness of a-C:H Films Prepared by the Methane Plasma Decomposition F.C. Marques, R.G. Lacerda (Universidade Estadual de Campinas - UNICAMP, Brazil) The major problem for the application of a-C:H is the substantial intrinsic stress usually present in films with high hardness. That hinders the use of hard carbon films in many applications where films thicker than few tenths of a micron are needed. It is extremely important, for technological application, the production of hard carbon films at low stress and, if possible, at high deposition rate. Recently, it has been reported that the incorporation of nitrogen and boron into the a-C:H network reduced the stress without changing the film hardness. In this work, it is reported a remarkable stress reduction of hard a-C:H films prepared at a relatively high deposition rate, without incorporating any strange element into the film network. The films were prepared in a conventional rf sputtering system, but used in a different way. They were deposited, at the same time, on both anode and cathode electrodes through the methane plasma decomposition. The films prepared on the anode are soft, but those prepared on the cathode are hard. The deposition rate of the films deposited on the cathode increases, from 0.1 to 2.4 ao A/s, as the negative bias voltage increases from 100 V to 1200 V. A significant decrease in the intrinsic stress (from 2.5 to 0.5 GPa) was obtained, with ony a slight reduction of their hardness (from 22 to 17 GPa), in the same bias range. Therefore, films with hardness of 17 GPa, stress as low as 0.5 GPa and deposition rate of 2.4 ao A/s were prepared. These are interesting properties for technological applications. The stress versus bias voltage curve presents a sharp peak in the 100 to 200 V bias range, similar to those observed in tetrahedral carbon films (ta-C and ta-C:H). This result gives major support to the sub-implantation model proposed to explain the formation of hard amorphous carbon films. In summary, hard amorphous hydrogenated carbon films were obtained under low stress and at high deposition rate.
4:10 PM		D2-2-9 Structural Investigations of Silicon Carbide Films Formed by Fullerene Carbonization of Different Substrates K. Volz, S Schreiber, M Zeitler, B. Rauschenbach, B Stritzker (University of Augsburg, Germany) Silicon carbide is a wide band gap semiconducter, which also has excellent mechanical properties. It can be used as a hard coating even in aggressive environs and at high temperatures due to its excellent chemical stability. Silicon carbide films of a thickness of up to one micron have been formed on silicon and silicon on sapphire substrates by evaporating fullerene (C60) molecules onto the heated targets. The influence of UV light irradiation during the carbonization has also been studied. The stoichiometry of the layers has been examined with Rutherford backscattering spectrometry. The results show, that it is possible to form stoichiometric (Si:C ratio 1:1) layers with this technique. The phase composition and microstructure of the films have been investigated by X-ray pole figure measurements and by cross sectional transmission electron microscopy. It is shown that the silicon carbide grows columnarily and mostly consists of the hexagonal phase. With this technique, silicon carbide films can be deposited onto several materials, if prior to carbonization a silicon film has been evaporated.