Papers

ICMCTF2004 Session D1-2: Carbon Nitride, Boron Nitride and Other Group-III Nitride Materials

Monday, April 19, 2004 1:30 PM in Room Royal Palm 4-6

Monday Afternoon

Start	Invited?	Item
1:30 PM		D1-2-1 Epitaxial Growth of Cubic Boron Nitride Films on Diamond at High Temperatures X.W. Zhang, H.G. Boyen, P. Ziemann (Universität Ulm, Germany) Beside their potential use as protective coatings for cutting tools and optical instruments, c-BN films have been considered as an ideal material for electronic devices applicable at high temperatures, since it is a wide-band-gap semiconductor and, unlike diamond, it can be doped both n- and p-type. For electronic device applications, however, single crystalline c-BN films appear necessary demanding for an epitaxial growth on top of a suitable substrate. To approach this goal, c-BN films have been prepared at elevated temperatures (900-1000°C) on top of CVD diamond films as well as diamond single crystals by means of ion beam assisted deposition (IBAD). The results of various characterization techniques unequivocally prove that 100% pure c-BN phase can be grown on top of diamond without any intermediate hexagonal BN layer that is commonly observed on various substrates. Additionally, the epitaxially grown samples exhibit smooth surfaces, and the magnitudes of their Young's modulus, their ultrahardness, as well as their rocking angles of 0.2° as observed by XRD corroborate their outstanding quality. Experimental conditions to achieve such high quality films will be discussed.
2:10 PM		D1-2-3 Cryogenic Deposition of Fullerene-like Carbon Nitride Thin Solid Films; Effect of Chemistry of the Film-forming Species and Substrate Temperature on the Growth Mechanisms J. Neidhardt, H. Högberg, L. Hultman (Linköping University, Sweden) Fullerene-like carbon nitride (FL CN_x) is a nanostructured thin film material consisting of bent and intersecting, nitrogen-containing graphitic sheets. It combines the unique properties of being hard and elastic, which results in a fracture tough and resilient material. Well-structured FL-CN_x thin films are commonly grown by DC reactive magnetron sputtering of graphite in an N₂/Ar mixture. Recent findings indicate that the structure formation is presumably due to the fact that the film forming flux consists to a large extent of multi-atomic C_xN_y species. Precursors with already preformed C-N bonds in the deposition flux might act as growth templates and in addition also enhance the desorption of volatile C₂N₂ from the growth surface, which may have a selective effect on preferentially bonded species and is therefore assisting the FL-structure evolution. In this work we investigated the extent of the desorption processes and their consequences on the resulting film microstructure, addressing in particular the effect of the chemistry of arriving species and the reactions at the growth surface. This was studied by varying the N₂-fraction from 0 to 1 and the substrate temperature from 900 down to 150 K. The results show that the incorporation rate of C and N into the film increases substantially with an increased N₂-content in the plasma and decreasing substrate temperature, thus indicating that the chemistry and magnitude of the arriving flux is substantially altered with the N₂-fraction in the discharge. The suppression of the thermally activated chemical desorption of C and N containing species at cryogenic temperatures strengthen this finding and results in the conclusion that the chemically activated desorption in conjunction with the varying chemistry of the film-forming flux affects the sensitive structural equilibrium, determined by incorporation and desorption of C_xN_y species.
2:30 PM		D1-2-4 Growth of Carbon Nitride Thin Films by Low-energy Ion Beam Assisted Evaporation: on the Production of Fullerene-like Microstructure Raul Gago, M. Vinnichenko, U. Kreissig (Forschungszentrum Rossendorf, Germany); Z. Czigany (Hungarian Academy of Sciences, Hungary); A. Kolitsch, W. Moeller (Forschungszentrum Rossendorf, Germany) Low-energy (<100eV) ion bombardment has been shown to be a key parameter in the production of hard and elastic carbon nitride (CN_x) thin films with fullerene-like (FL) structure¹. The production of FL-CNx is mostly reported for reactive magnetron sputtering but still the growth mechanisms are not clear². In this way, the growth by ion beam assisted deposition (IBAD) would provide a better understanding since the source of neutrals and ions are independent. In this work we study the growth of CN_x films produced by e-beam evaporation of graphite and simultaneous low-energy N₂ ion assistance at different substrate temperatures. The low-energy ions were provided by an End-Hall ion source. The samples were characterized by spectroscopic ellipsometry, elastic recoil detection analysis (ERDA), Raman and high resolution transmission electron microscopy (HRTEM). Despite the low-energy ions, a high thermal-activated re-sputtering of the deposited films has been observed, indicating its chemical origin. In addition, the maximum nitrogen content in the films is limited to ~25 at.%, which should be related to the re-sputtering process. The Raman spectra and the optical properties indicate the dominance of sp² hybrids. However, the results differ from those of FL-CN_x, indicating that the sp² hybrids are not arranged in a FL microstructure. This is also corroborated by HRTEM, where the samples were found to be mainly amorphous. Therefore, our results suggest that low-energy ion bombardment is not the main driving force for the promotion of FL arrangements, although this condition may be necessary to avoid damage on the growing microstructure. In this sense, the incorporation of neutrals, such as C_xN_y species formed during magnetron sputtering, may play a dominant role for the growth of FL-CN_x [3]. [1] Sjöstrom et al. Phys. Rev. Lett. 75 (1995) 1336. [2] Hultman et al. MRS Bulletin 28/3 (2003) 194. [3] Neidhardt et al. J. Appl. Phys. (in press).
2:50 PM		D1-2-5 Effect of the Bias Voltage on the Structure of Carbon Nitride Films A. Champi, F.C. Marques (IFGW/UNICAMP, Brazil) The effect of the bias voltage on the structural, optical and mechanical properties of amorphous carbon nitride films deposited by the plasma decomposition of methane (CH₄) and nitrogen (N₂) atmosphere, is investigated. A series of films was deposited under the condition in which diamond-like a-C:H films is obtained, i.e, bias of -200 V, and pressure of 1.0Pa. Another series of films was deposited under the condition graphitic-like films is obtained, i.e, bias of -800 V, and pressures of 12 Pa. In order to investigate the effect of these conditions on the properties of the films, optical, nanohardness, EELS, and stress measurements were undertaken. It was observed that the incorporation of nitrogen and the investigated properties depend on the starting structure (diamond-like vs. graphitic-like). The use of high gas pressure and high bias allowed the preparation of stable and thick (>1 micron) nitrogen-carbon films, with high hardness (18 GPa), and low stress (0.5 GPa) deposited at relatively high deposition rate (0.5 nm/s).
3:10 PM		D1-2-6 Deposition of Ti-B-N (Single and Multilayer) and Zr-B-N Coatings by CVD Techniques on Cutting Tools in Industrial Scale Equipment H Holzschuh (Walter AG Germany) Coatings in the system Ti-B-N and Zr-B-N were investigated for potential in cutting steel and cast iron. Therefore TiN, TiB₂, Ti-B-N, multilayers like [TiN-TiB₂]_x or [TiN-TiBN]_x and Zr-B-N coatings were deposited on cemented carbides using chemical-vapor deposition (CVD). When keeping the Boron content larger than 5% Ti-B-N coatings resulted in mixtures of TiN and TiB₂. The TiN:TiB₂ ratio, microstructure, hardness and wear resistance of the coatings were controlled by varying deposition temperatures and gas flows in the CVD process. Compared to TiN and TiB₂ coatings deposition rates in Ti-B-N coatings became noticeable higher. Results showed that Ti-B-N coatings exhibited high hardness (HV3500 to HV5000) at moderate deposition temperatures (700°C to 900°C). Deposition temperatures below 900°C successfully suppressed Boron diffusion and formation of a CoWB phase on the surface of the cemented carbide tool. Due to the moderate deposition temperatures Ti-B-N coatings showed very good adhesion. Boron diffusion was responsible for poor adhesion in TiB₂ coatings. For milling tests TiN, TiB₂, Ti-B-N and multilayer coatings with a TiB₂ content of 10% to 95% were investigated. All Ti-B-N coatings showed good wear resistance against abrasion. At a certain level of the TiN:TiB₂ ratio the Ti-B-N coatings suppressed thermal cracks. Although the Zr-B-N and the Ti-B-N system seemed to be very similar, results showed differences in deposition chemistry and properties.
3:50 PM		D1-2-8 Chromium-copper Based PVD Metallic Nanocomposite and Amorphous Coatings: Microstructure, Mechanical and Tribological Properties C. Tsotsos, A. Leyland, A. Matthews (University of Sheffield, United Kingdom); M. Baker (University of Surrey, United Kingdom) Chromium-Copper based metallic nanocomposite coatings produced by sputter PVD can provide high hardness (H) with a relatively low elastic modulus (E), closely matching that of a typical substrate. The coating can thus better accommodate substrate deformation under load without failure. Interstitial additions of nitrogen (at temperatures < 400°C) for a Cu content of between 5 to 20 at.%, can promote a nanostructure tending to Cr(N) metallic nanocrystals surrounded by an amorphous Cu intergranular phase. Above 20 at.% Cu, coatings appear to be of a quasi-amorphous dual-phase nanostructure. Such Cr-Cu-N based metallic nanocomposite coatings demonstrate microhardness values up to 60GPa (i.e. "ceramic"hardness), but with an elastic modulus closer to that of Cr metal (i.e. 280GPa). Furthermore, these coatings generally exhibit high toughness and resilience in ball-on-plate impact wear and surprisingly good sliding wear resistance in some cases. Complete amorphisation of the Cr-Cu-N system can occur over a wide composition range with further (substitutional) additions of Ti and (interstitial) B. Cr-Ti-Cu-B-N coatings exhibit X-ray spectra characteristic of a glassy structure, demonstrating microhardness values between up to 40GPa with similar (and in some cases better) impact and sliding wear resistance to equivalent coatings in the Cr-Cu-N system despite being less hard than the latter. Very little change in structure is apparent in XRD analysis of glassy Cr-Ti-Cu-B-N coatings after vacuum annealing for one hour at temperatures up to 600oC. However, certain compositions exhibit a hardness increase of up to 40% over their as-deposited values when annealed. Further investigation of such phenomena is required but, in general, metallic Cr-Cu-N nanocomposite and Cr-Ti-Cu-B-N glassy-metal coatings can be used to significantly enhance the wear resistance of AISI 316 stainless steel and other low-modulus, low-strength substrate materials.
4:10 PM		D1-2-10 Characterization of BCN Films Deposited by Reactive Cathodic Arc Evaporation P.C. Tsai (National Huwei Institute of Technology, Taiwan, R.O.C.); K.H. Chen (Academia Sinica, Taiwan, R.O.C.) The Boron carbon nitride (BCN) thin films were deposited by reactive cathodic arc plasma deposition (CAPD) with B, C containing target in an Ar/N₂ mixture. The portion of N₂ in the gas was varied with the substrate at different floating bias. The characteristics of the films were investigated using Raman spectroscopy, atomic force microscope (AFM) and nanoindentation tester. The microstructures of the films were evaluated using field emission scanning electron microscopy (FEGSEM), X-ray diffractometry (XRD) and high-resolution transmission electron microscopy (HRTEM). X-ray photoelectron spectroscopy (XPS) and Fourier-transformed infrared spectroscopy were used to analyze the bonding structure of the films. The results showed that well adhesive BCN films were synthesized on the silicon substrate successfully. The FEGSEM showed that the films reveal a crystalline structure. The Raman spectra showed that the wavenumber ranging from 900 to 1800cm^-1 consists of D band and G band, similar to that of cathodic arc plasma deposited DLC. The effects of processing parameters on the deposition rate, film morphology, roughness, and nanohardness of the deposited films were evaluated. The high-resolution transmission electron microscopy (HRTEM) studies on the films and the bonding structure of the films will also be discussed.
4:30 PM		D1-2-11 Boron Carbon Nitride As a pH Sensing Membrane S Chattopadhyay (Academia Sinica, Taiwan, R.O.C.); C.L. Lee, B.R. Huang (National Yunlin University of Science and Technology, Taiwan, R.O.C.); K.H. Chen (Academia Sinica, Taiwan, R.O.C.); L.C. Chen (National Taiwan University, Taiwan) Sensors are an important part of analytical studies. Ion sensitive field effect transistor (ISFET) was first used for chemical sensing by P. Bergveld.¹ ISFET can now be applied to pH, pK, pNa sensing and other ion detection devices. Oxide and nitride sensing membranes such as SiO₂, Al₂O₃, Ta₂O₅, SnO₂ and Si₃N₄ were all used as pH sensors. Chemically inert sensing membranes such as diamond like carbon has also been used in ISFET for pH measurements. Recently, boron carbon nitride (BC_xN_y) material is widely studied since it showed superhard properties. Although detail composition analysis and bonding characterizations have been reported for this a-BC_xN_y material, such an application as a pH sensing membrane has not been tried. In this study, amorphous boron carbon nitride (a-BC_xN_y) has been used as the sensing membrane in an extended gate field effect transistor (EGFET) for the measurement of pH of solutions. The a-BC_xN_y material was produced by dual gun magnetron sputtering and has been found to be a stable and sensitive pH sensor with sensitivities near 40mV/pH. An increasing sensitivity was found with increasing carbon content in the a-BC_xN_y sensing membrane and reached a maximum of 46 mV/pH for a carbon concentration of 47 at. %. The drain current, which is an indicator of the pH, remained fairly stable, within few microamperes, over a period of ten minutes in the phosphate solution with varied pH, demonstrating a good stability of the sensing membrane. The sensitivity, stability and reproducibility of the a-BC_xN_y membrane in the sensing device will be discussed and demonstrated. ¹P. Bergveld, IEEE Trans. Biomed. Eng. BME-17, 70 (1970).