Papers

ICMCTF2004 Session D2-1: Diamond-like Carbon, Diamond and SiC Materials

Tuesday, April 20, 2004 1:30 PM in Room Royal Palm 4-6

Tuesday Afternoon

Start	Invited?	Item
1:30 PM		D2-1-1 Transparent Nanocrystalline Diamond Film on Large Area Glass Substrate Y. Koga (National Institute of Advanced Industrial Science and Technology, Jaoan); K. Tsugawa, H. Hasegawa (National Institute of Advanced Industrial Science and Technology, Japan); M. Shelby, M. Liehr (Applied Films GmbH & Co KG, Germany) A high quality, transparent, smooth nanocrystalline diamond film was successfully grown on a glass substrate using the microwave eight parallel antenna plasma system. The deposition was carried out using a CH₄/@H₂plasma maintaining the substrate temperature at 450 - 500@sub o@C. The growth rate of the film was 50 nm/hour. The films are smooth and uniform over an area of 30 × 30 cm₂ and exhibit strong adhesion to the glass substrate. UV Raman spectroscopy (244 nm excitation wavelength) shows a high quality diamond film by the sharp peak at 1333 cm@sub -1@. X-ray diffraction analysis indicates that the film consists of nanocrystal diamond, i. e., the crystallites range in size from 10 to 20 nm. From TEM observation the nanocrystalline diamond constituted of 5-20 nm in size was formed densely. The transmittance in the visible region of a nanocrystalline film with a thickness of approximately 500nm is 90 % in average at a wavelength between 400 nm and 800 nm. This high transmittance in the visible light region makes it possible to coat glass windows with diamond film for use in abrasive or other extreme environments.
2:10 PM		D2-1-3 Hot Filament Chemical Vapour Deposition of Nanocrystalline and Polycrystalline Diamond Coatings onto Interlayered Steel Surfaces W Ahmed, M. Amar (Manchester Metropolitan University, United Kingdom); S. Kumashiro (Salford University, United Kingdom); J. Colligon (Manchester Metropolitan University, United Kingdom); S.L. Donnelly (Salford University, United Kingdom) Abstract It has been established that the deposition of diamond films onto various substrates results in significant technological advantages. Diamond is hard, wear resistant, chemically inert and biocompatible and therefore the ideal material for surfaces of cutting tools and biomedical components. However, it is well known that diamond deposition onto ferrous substrates is problematic due to low nucleation densities and poor adhesion. Previous studies have reported the application of interlayer materials such as metal nitrides and carbides have been used to provide bonding between diamond and steel. However, in this study we have investigated the use of a nanocomposite layer of TiN/Si₃N₄ deposited by dual ion beam deposition system to provide a nucleation and adhesion base for subsequent diamond growth. A modified hot filament CVD system has been used to deposit polycrystalline and nanocrystalline diamond films. The effects of ion beam energy on subsequent diamond nucleation and growth have been investigated. It has been found that the use this novel nanocomposite interlayer is an effective method of improving adhesion between the diamond film and the steel substrate.
2:30 PM		D2-1-4 Nucleation of Polycrystalline Diamond on WC-Co using Bias Enhancement Together with the Newly Developed Time-modulate CVD G Cabral, V.F. Neto, N. Ali, J. Gracio (University of Aveiro, Portugal) It is well know that nucleation and grow of diamond films can be enhanced throw the application of polarization electric fields. In this paper, we report the investigation of joining bias enhancement techniques with the newly developed time-modulates CVD process, applied to the study of nucleation enhance on WC-Co hardmetals with 6%Co and WC grain size from 0.8 to 6 micron. It is also reported the optimised conditions to archive a quality dense plasma at the deposition site, using a mixture of CH₄/H₂ and Ar/H₂ gases. The polycrystalline diamond films deposited, where characterized for their morphology, namely nucleation density and preferred nucleation spots, crystal orientation and size by means of SEM and AFM and for diamond quality by micro-Raman Spectroscopy. Preliminary results show that nucleation density, adhesion and surface properties are increase in all the four grades studied and Raman film quality is maintained.
2:50 PM		D2-1-5 Studies OF CVD Diamond Applications as Ultrasound Abrading Devices V.J. Trava-Airoldi (INPE/MCT-Instituto Nacional de Pesquisas Espaciais-Brazil); E.J. Corat (INPE/MCT-Instituto Nacional de Pesquisas Espaciais, Brazil); J.R. Moro (Universidade Sao Francisco - USF, Brazil) Very accurate, durable and noiseless tools for many application has been of interest by a lot of researchers, mainly for cutting materials as hard as ceramic and as soft as bone. However, the adherence between the substrate and the diamond film has not been good enough to support ultrasound energy while in contact with hard surfaces. In this work are presented studies concerning the obtainment of CVD diamond coating on different forms of metallic substrate with very good adherence in order to be applied as na abrading device for ultrasound equipment. This kind of technique is powerful for hard material cutting and polishing with very good accuracy, noiseless, etc.. Diamond coating has been obtained by using a Hot Filament Assisted Technique, with high growth rate using conventional hydrogen and methane gas mixtures. Small and special metallic rods, in the form of a diamond bur, with pre-prepared surface, was coated by thick diamond film with very high adherence to the substrate. Life time testing in abrading conditions on hard ceramic has been made, showing very good performance. Ultrasonic CVD diamond tips are around 30 times more durable than the conventional ones. In terms of cutting accuracy CVD diamond tips in ultrasound equipment has been tested on hard ceramic, glass and bone surfaces. In all tests, the cutting regions present no damaged edges and the bore diameter keep accurate values while the tips lasts. The morphology and roughness analyses of the abraded surface has been evaluated by SEM and AFM techniques. An important application of this device, presented at the first time related to dentistry, will also be discussed.
3:10 PM		D2-1-6 Synthesis of Diamond Films and Nanotips Through Graphite Etching Q. Yang (University of Saskatchewan, Canada) A new hot filament CVD process, in which the graphite is etched with hydrogen, has been developed to synthesize diamond films and nanotips. P-type (100)-oriented silicon wafers were used as substrates. The graphite plate was placed below or beside the silicon substrate and only hydrogen was supplied during the process. High quality diamond films with high growth rate were synthesized without discharge. The diamond growth rate is 4 times higher than that through conventional hot filament chemical vapor deposition using a gas mixture of methane and hydrogen (1 vol. % methane) under similar deposition conditions. The diamond films synthesized using this process exhibit smaller crystallites, smoother surface and contains smaller amount of non-diamond carbon phases. When a DC glow discharge between the filament (anode) and the substrate holder (cathode) is initiated, well-aligned diamond nanotips were formed on the diamond surfaces.
3:30 PM		D2-1-7 Investigation of the Growth Mechanism and Structure of Nanocrystalline Diamond Films by Rapid Thermal Annealing W. Kulisch (Institute for Health and Consumer Protection, Italy); C. Popov, S. Boycheval (University of Kassel, Germany); G. Beshkov (Bulgarian Academy of Sciences, Bulgaria); V. Vorlicek (Academy of Sciences of the Czech Republic); P.N. Gibson (Institute for Health and Consumer Protection, Italy); G. Georgiev (University of Kassel, Germany) Nanocrystalline diamond (NCD) films in an amorphous matrix have been deposited by microwave plasma chemical deposition from CH₄/N₂ mixtures with varying methane contents. They have been characterized by a variety of methods with respect to their morphology and structure, composition, crystallinity, and bonding environment. It was found that, although the CH₄ concentration in the gas phase has a pronounced influence on the macroscopic appearance of the films, the microscopic structure and the bonding environment are almost unaffected. Further insights into the structure of the films and the underlying growth mechanisms were gained by rapid thermal annealing (RTA) experiments performed at 1100°C and 1400°C for 3 min in vacuum. Following the RTA treatment, the samples were analysed by SEM, XRD, Raman and FTIR. The temperature treatment left the diamond nanocrystals almost unaffected but destroyed the matrix which, according to the above mentioned analyses, consists of a mixture of sp² bonded carbon and sp³ bonded CH_x units. It became evident that the NCD fraction of the films started to grow from nucleation sites created by the ultrasonic pretreatment of the substrates with diamond powder, and continues via frequent secondary nucleation on already grown crystallites leading to a ballas or cauliflower-like structure which is obscured in the as-grown films by the amorphous matrix surrounding the diamond nanocrystallites.
3:50 PM		D2-1-8 Decay Mechanisms of Ion Induced Electron Emission in CVD Diamond Films V. Richter (Technion-Israel Institute of Technology, Israel) CVD diamond films are commonly regarded as a promising material for cold cathodes with high ability to emit electrons by absorbing different types of penetrating radiation or, alternatively, by an external electric field. Since the bombardment of these films by primary electrons or other charged particles (including atomic and molecular ions) is followed by extremaly high secondary electron (SE) emission yield, CVD diamond films can be used as a very sensitive detector of such particles. These potential advantages are, however, hindered by the fact that SE emission decreases under radiation impact and, specifically, ion bombardment because of different effects of ion-material interaction which are inherent to CVD diamond films. By studying ion induced electron emission (IIEE) yield as a function of radiation dose one can discern fast and slow changes in this yield and surmise different mechanisms of material degradation. Particularly, we show here that fast changes are dependent on the film conductivity and doping while slow ones are defined by the surface hydrogen termination and its desorption, and by gradual accumulation of radiation defects in the region of SE escape depth. On that basis, we establish the importance of material parameters such as grain size, film thickness and doping, and the necessity of surface hydrogen termination for best performance of CVD diamond films as durable electron sources or detectors.
4:10 PM		D2-1-9 Electron Emission Characteristics Controlled by Metal Intermediate Layer between Nanotips of Amorphous Diamond and ITO Substrate M.C. Kang, J.L. Huang (National Cheng Kung University, Taiwan, R.O.C.); J.C. Sung (Taipei University of Technology, Taiwan, R.O.C.); H.K. Chang (National Cheng Kung University, Taiwan, R.O.C.) Different interlayer materials (W, Cr, Ti, Mo) sandwiched between amorphous diamond emitters and ITO substrates were found to affect the emission current. Specifically, the metal interlayer can alter the surface morphology of amorphous diamond coating and enhance the field enhancement factor for electron emission. Moreover, the metal/diamond structure could also obtain low power levels for the electron emission. With the comparison of various interlayer materials, it was found that amorphous diamond/Mo/ITO sandwich could provide the best emission results with the lowest turn-on applied field (4.3 V/um at 10 mA/cm²). The high emission current was due to the high aspect ratio of nanotips for deposited amorphous diamond. This high aspect ratio concentrated the applied field more on the emission tips so a higher emission flux was observed. The field emission of amorphous diamond deposited on various substrates was highly reproducible.
4:30 PM		D2-1-10 Influence of Nanoscale Inhomogeneity on the Electronic Properties of DLC Films J.D. Carey, S.R.P. Silva (University of Surrey, United Kingdom) The presence of differently hybridized forms of carbon in diamond-like carbon thin films has a profound effect in determining the optical and electronic properties of the films. Films can be considered as consisting of more conductive nanometer sized sp² clusters embedded in an sp³ electrically insulating matrix. We show that it is the degree of clustering within the sp² phase plays an important role in explaining many of the electronic properties of these films. By changing either the film deposition conditions or by using ion beam implantation we show that the delocalization of the electron wavefunction can be altered and the influence of stress on the bandstructure. An understanding of the extent and nature of clustering of the sp² phase is shown to be important in explaining the reduction of the electron spin resonance linewidth with increasing spin density whereby a purely dipole-dipole interaction between spins would be predicted to increase the linewidth with spin density. This observed reduction of the linewidth is attributed to intra-cluster delocalization as a result of the exchange interaction. Results from scanning tunneling microscopy and electrical measurements show the importance of cluster-to-cluster electron hopping (inter-cluster delocalization) in the transport and electron field emission properties of the films. Extensions of this model to other materials systems are also discussed.
4:50 PM		D2-1-11 The Large-area Free-standing CVD Diamond Wafer Fabrication by DC PACVD W.-S. Lee (Korea Institute of Science and Technology, South Korea); K.-W. Chae (Precision Diamond Tech. Co. Ltd., South Korea); Y. J. Baik (Korea Institute of Science and Technology, Korea) The high-rate, large-area fabrication of the free-standing diamond wafer has been the long-term goal of the CVD diamond society. The 6 or 7 inch CVD diamond wafer fabrication by the dc arc jet and the microwave PACVD had been reported in the recent years. In this paper, we report the successful high-rate fabrication of the free-standing CVD diamond thick film wafers, with diameters up to 8 inch (200mm) using our proprietary deposition technique. DC PACVD with the diode-type electrode configuration was used. Methane-hydrogen gas mixture was used as the precursor gas. The methane content in hydrogen was 3~9% by volume. The flow rate of the gas was 600~1000 sccm. The chamber pressure was 80 ~ 130 torr. The voltage and current supplied to the plasma was 800~1000V and 100~120A, respectively. The substrate temperature was 1100~1250°C as measured by the optical pyrometer. The thermal property was characterized by the converging thermal wave technique. The crystal quality was analyzed by the macro-Raman spectroscopy. The thickness was measured by the thickness gauge. The surface microstructures were analyzed by optical microscopy as well as SEM. The thickness of the wafers were in the range of 500~1000µmm depending on the deposition time. At the optimized deposition conditions, the deviation of thickness and the thermal conductivity could be reduced below 10% of the respective averaged values. The distribution of FWHM of Raman diamond peak over the wafer surface also showed excellent uniformity. The extremely simple scale-up of the present deposition process will also be demonstrated.