Papers

ICMCTF2002 Session D2-1: Synthesis and Characterization of Diamond, Ternary Phase and other Carbon-based Materials

Wednesday, April 24, 2002 8:30 AM in Room Royal Palm Salon 1-3

Wednesday Morning

Start	Invited?	Item
8:30 AM		D2-1-1 Hard Coatings by Conversion of Silicon Carbide to Diamond-Structured Carbon Y. Gogotsi (Drexel University); S. Welz, M.J. McNallan (University of Illinois at Chicago) Commercially used chemical vapor deposition (CVD) of diamond has serious limitations because of the low production volumes and high cost. We report synthesis of nano- and microcrystalline diamond by extraction of silicon from silicon carbide in chlorine-containing gases at ambient pressure and temperatures not exceeding 1000°C@. No plasma or other high-energy activation is required, thus providing an opportunity for large-scale production. Presence of hydrogen in the gas mixture leads to a complete conversion of SiC to diamond with the average crystallite size of 5-10 nm. Thick (>50 microns) and thin (several nanometers) coatings can be made using this method. The linear diamond growth kinetics allows transformation to any depth, ultimately till the whole SiC particle or component is transformed to diamond. Nanocrystalline diamond coatings demonstrate hardness values in excess of 50 GPa and Young's modulus up to 800 GPa.
9:10 AM		D2-1-3 Very High Growth Rate Chemical Vapor Deposition of Single-Crystal Diamond C-S. Yan, Y.K. Vohra (University of Alabama at Birmingham); R.J. Hemley, H-K. Mao (Carnegie Institution of Washington) Diamond produced by low-pressure chemical vapor deposition (CVD) is the most promising technology for producing low cost and high quality large diamond1,2. Nevertheless, the widespread use of CVD diamond in many applications has not been successful due to the existence of grain boundaries of polycrystalline diamond that is produced and slow growth rate (typically 1 um/h). Here we report microwave plasma chemical vapor deposition of high-quality single-crystal diamond with smooth transparent surfaces and other characteristics identical to that of the high-pressure, high-temperature synthetic diamond used as the substrate. The single crystals can be produced at growth rates of 50 um/h, which is up to two orders of magnitude higher than standard processes for making polycrystalline CVD diamond. This high-quality single-crystal CVD diamond should find numerous important applications in electronic devices, as high-strength windows, and in a new generation of high-pressure instruments requiring large single-crystal anvils.
9:30 AM		D2-1-4 Decrystallization of Diamond Under Pulsed Excimer and YAG Lasers and Subsequent Lattice Relaxation A. Badzian, R. Roy, T. Badzian, W. Drawl, P. Mistry, M.C. Turchan (Penn State University); K.A. Cherian (QQC Inc.); R. Martukanitz, V. Semak, T.M. Petach (Penn State University) Surface modification by multiple laser process is an effective modern tool for surface engineering technologies for metals, ceramics and plastics. Interaction of laser fluxes with a target created a challenge to understanding structural changes in the atomic scale. This report refers to the decrystallization of diamond. Lattice distortions were introduced to diamond polycrystalline coating and to diamond single crystals exposed to simultaneous excimer and Nd:YAG pulsing lasers in air ambient. The rough surface of polycrystalline coating was ablated and smoothed. The top layer of the coating during smoothing was turned to amorphous according to disappearance of the 1332 cm-1 Raman peak. The atomic disorder was gradually relaxed during three years, and Raman signature reappeared. X-ray diffraction data indicate on lattice distortion of the first kind. Lattice disorder of diamond is treated from a broad perspective; and Fourier transform analysis is applied to diffraction issues. In a separate experiment a single crystal diamond was placed at the focal spot of the excimer laser and was heated by the Nd:YAG laser. This experiment did not reach the state of amorphization; however, intensity of Raman peak dropped four times and regained the full peak height after annealing in hydrogen plasma. A combination of pressure waves and heating and cooling cycles stands behind the introduction of atomic disorder.
9:50 AM		D2-1-5 Enhancing Nucleatin Density & Adhesion of Polycrystalline Diamond Films Deposited by HFCVD Using Surface Treatments on Cemented Tungsten Carbide H. Sein, N. Ali, W. Ahmed, I. Hassan, C. Rego (Manchester Metropolitan University, United Kingdom) Deposition of diamond films onto tungsten carbide is attractive since it can lead to potential improvements in life and performance of dental burs. However, deposition of diamond onto WC-Co dental burs and inserts are problematic due to WC contains cobalt as a binder, which provides additional toughness to the tool but it causes poor adhesion and low nucleation density. There are a number of potential surface treatments, which can be used to overcome these problems including chemical etching, ion implanting, interlayer coating and bias treatment. Negative biasing of the substrate is attractive because it can be controlled precisely, it is carried out in-situ, gives good homogeneity and results improved adhesion. On flat substrates such as copper and silicon biasing has been shown to give better adhesion, improved crystallinity and smooth surface. In this study we have used a modified vertical filament HFCVD system to coat complex shaped tools such as dental burs with polycrystalline diamond films, which has good adhesion and crystallinity. By applying a negative substrate bias we show that nucleation density, adhesion and surface properties can be improved. The effects of various process parameters such as bias voltage, bias time, methane concentration, working pressure and the filament arrangement on the film properties have been investigated. . For machining abrasive tools the hard, wear resistant CVD diamond films must be of good quality (homogeneity, crystallinty, structure, grain size, roughness) and show strong adhesion.
10:10 AM		D2-1-6 Time-modulated Deposition of Smooth Polycrystalline Diamond Films Using CVD N. Ali, Q.H. Fan, T.B. Huang, J. Gracio (University of Aveiro, Portugal) The deposition of smooth polycrystalline diamond films has been carried out using a time-modulated chemical vapour deposition (TMCVD) method. TMCVD can be characterised as the alternative introduction of methane (at relatively higher concentration) in shorts bursts into the vacuum chamber during deposition followed by the extended growth duration at a lower methane concentration. The newly proposed TMCVD method was designed to (a) deposit optically smooth films; (b) control film microstructure and morphology; and (c) improve film reliability and repeatability. Conventional CVD methods produce coatings which display variations in crystal size, crystal orientation, surface roughness and film morphology. The newly proposed thin film deposition method produced films that displayed surface roughness values (Ra) of the order of ~ 0.25 μm. This is a great improvement from the films produced by the conventional CVD method where the films displayed surface roughness of 0.3 μm. In addition, films deposited by the TMCVD method displayed higher growth rates as compared to the conventional CVD method. Growth rates of the order of 3.3 μm/hour were obtained with TMCVD and 2.4 μm/hour with conventional CVD. Film microstructure together with grain size and film morphology was more consistent with TMCVD as compared to conventional CVD. Scanning electron microscopy (SEM) and Raman spectroscopy was used to characterise the deposited films for microstructure, morphology, crystallinity and carbon phase purity.
10:30 AM		D2-1-7 Fabrication of Tubes of Diamond with Micrometric Diameters and Their Characterization V. Baranauskas (University of Oxford, United Kingdom); H.J. Ceragioli, A.C. Peterlevitz, S.F. Durrant (Universidade Estadual de Campinas, Brazil) The fabrication and characterization of diamond tubes obtained by chemical vapor deposition (CVD) is reported. Such tubes are of interest in diverse applications, such as micro-drilling tools, wave-guides, field-emission devices, bio-medical implants and so on. Diamond was deposited onto tungsten wires with diameters of between 100 and 600 ïm; the tungsten cores were subsequently completely removed by etching, to leave self-sustained diamond and diamond-like carbon tubes. A hot-filament CVD system fed with ethanol highly diluted in hydrogen was employed. Cross-sections of the samples revealed the familiar columnar growth structure, but the nucleation and growth on such cylindrical substrates differ from those observed for flat surfaces. These effects are discussed in relation to morphological data obtained by scanning electron microscopy (SEM) and results from Raman spectroscopic analyses of samples produced at different deposition temperatures. The feasibility of the use of this technique for the production of diamond micro-tubes is demonstrated.
10:50 AM		D2-1-8 Cathodoluminescence Characteristics of Polycrystalline Diamond Films Grown by Cyclic Deposition Method S.H. Seo, W.C. Shin, J.S. Park (Hanyang University, Korea) Diamond, with its unique properties, has been considered as a promising material for versatile applications in tool coatings, optical components, and electronic devices. With the recent progress of chemical vapor deposition (CVD) technology using plasma, polycrystalline diamond films with properties approaching those of nature diamond can easily be grown at relatively low temperatures in a reproducible and controlled environment. However, the CVD-produced polycrystalline diamond films inevitably include inherent defects and non-diamond carbon phases which may have dramatic effects on their optical and electronic properties. As one of methods obtaining the high-quality diamond films, cyclic deposition technique, modulating the growing-step (CH₄ + H₂ plasma) and etching-step (H₂ plasma), has been proposed. The Raman spectroscopy has been the most widely used to examine the microstructures of diamond films grown using the cyclic deposition. However, with the Raman spectra, there exist some ambiguities in identifying the defects generated during the cyclic deposition. Recently, it has been suggested that cathodoluminescence (CL) spectroscopy provides a powerful and highly sensitive technique to investigate the nature of diamond defects. In this paper, we for the first time present the cathodoluminescence characteristics of diamond films grown using the cyclic deposition method. The microwave plasma- assisted CVD system was used to grow the diamond films under the nominal condition of 40 Torr in pressure, 0.5 % in CH₄/H₂ ratio, 710 °C in temperature, and - 200 V in the bias-enhancement for nucleation. The cyclic modulation ratio of etching (T_E) to growth (T_G) was varied ranging from 0 to 2.33 with the whole deposition time fixed (120 min). From the measurement of full-width half-maximum (FWHM) and I_D / I_G intensity ratio obtained using the Raman spectra, it was confirmed that both diamond defects and non-diamond carbon phases were noticeably reduced by adopting the cyclic deposition method. The CL spectra obtained from these films have showed the following spectral features: the so-called band-A at about 430 nm and the nitrogen-related bands at about 578 nm and 637 nm. As the cyclic modulation ratio (T_E/T_G) was increased, the relative intensity ratio of band-A to nitrogen-related bands (I_A/I_N) was decreased. From the additional measurements using the x-ray diffraction (XRD) and scanning electron microscope (SEM), it was elucidated that the CL characteristics of deposited diamond films were closely related to the crystal orientations and film morphologies. In addition, the effects of post-hydrogen treatment and intentional nitrogen-injection on the changes of diamond defects will also be discussed.