ICMCTF2003 Session D2-1: Growth and Applications of Diamond DLC, and other Wide Band Gap Materials

Wednesday, April 30, 2003 1:30 PM in Room Royal Palm 1-3

Wednesday Afternoon

Start	Invited?	Item
1:30 PM	Invited	D2-1-1 Atomic-scale Modelling of the Growth of Carbon Structures R. Nieminen (Helsinki University of Technology, Finland) The combination of atomistic, first-principles calculations with molecular-dynamics simulations, kinetic Monte Carlo methods, cellular automata techniques and eventually macroscopic continuum equations enables a multiscale approach for computational studies of materials growth and processing. In this talk, I discuss recent advances in the various computational and theoretical methods and comment on their accuracy and predictive power. As specific examples, I present recent results for the growth and processing of carbon structures (amorphous and crystalline films, including their doping, multishell fullerenes, and nanotubes). In addition, theoretical results relevant to the recent reporting of ferromagnetism in carbon are presented. Similar multiscale techniques have also been applied to modelling of anisotropic wet etching of diamond-structured materials. These results are also discussed.
2:10 PM		D2-1-3 Influence of the Deposition Conditions on the Structure of Tetrahedrally Bonded Amorphous Carbon Films - a Simulation Approach B. Schultrich (Fraunhofer Institute for Material and Beam Technology Dresden, Germany); H.U. Jäger (Institut für Ionenstrahlphysik und Materialforschung, 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. A more detailed analysis shows that several stages should be considered corresponding to different dominating processes on very different time scales. For investigation of the film growth in the short time impact stage molecular dynamics was used. For this purpose the empirical interaction potential of Brenner was modified to describe film formation by hyperthermal species. By optimised codes and long-time calculations of several months, it was for the first time possible to simulate the stationary growth of carbon films of several nanometer thickness. The film structure (interface, diamond-like bulk film, graphitic top layer) was quantitatively analysed in dependence on particle energy and temperature. The results of the impact stage represent the input data for the long time diffusion stage. Based on continuum mechanics a simplified model for the further film formation has been developed. It describes the formation of the different carbon structures (characterized by the density or the corresponding sp² : sp³ ratio) as a competition of subplantation and relaxation, so it becomes possible to quantify the influence of more complex technological parameters like beam energy distribution and thermal transport. The characteristic tendencies extracted from these technological maps are discussed and compared to experimental results.
2:30 PM		D2-1-4 Preparation and Properties of Pulsed Laser Deposited Diamond-Like Carbon Films S. Weissmantel, G. Reisse, D. Rost (University of Applied Sciences Mittweida, Germany) Diamond-like carbon films were prepared by pulsed laser deposition using 248 nm excimer laser wavelength and laser pulse energy fluences in the range of 6 to 30 J/cm². At those fluences the mean kinetic energies of the ablated species were in the range of 35 to 130 eV. Films prepared at substrate temperatures below 100°C are completely amorphous and have 80 to 85 % sp³ bonds (determined by EELS). As-deposited films show high compressive stresses in the range of 8 to 10 GPa. We investigated the possibilities to reduce those stresses by means of thermal annealing (as known from the literature [1]) and, in particular, by means of pulsed laser annealing. We will show that both methods allow the preparation of stress-free diamond-like carbon films with thicknesses of several micrometer and good adherence to Si, SiO₂, WC hard metal and Ge substrates. Critical loads up to 30 N (on Si) and 50 N (on WC) have been measured by means of scratch test. The optical and mechanical properties of those films have also been measured. Films have optical band gaps up to 2.5 eV and average surface roughnesses of 1.0 to 1.5 nm (on Si). Their Vickers microhardness was measured on 2 µm thick films on WC to be 85 to 95 GPa by using a dynamic indentation method. The Young´s modulus is about 800 GPa and the density some 3.3 g/cm³ (both determined by acoustical surface wave spectroscopy). In a final part some examples on laser microstructuring of those films using femtosecond laser pulses and on the preparation of free-standing membranes and ultrathin films will be shown. [1] T.A. Friedmann, J.P. Sullivan, J.A. Knapp, D.R. Tallant, D.M. Follstaedt, D.L. Medlin, P.B. Mirkarimi, Appl. Phys. Lett. 71, 26 (1997) 3820.
2:50 PM		D2-1-5 Structure and Properties of DLC Based Coatings Prepared by Reactive d.c. Magnetron Sputtering K. Bewilogua, R. Wittorf, H. Thomsen, M. Weber (Fraunhofer IST, Germany) Metal containing diamond-like carbon (a-C:H:Me) coatings commonly will be prepared by reactive d.c. magnetron sputter deposition with acetylene as reactive gas. The targets consist of transition metals, e.g. tungsten or titanium or of transition metal carbides. It is well known that a-C:H:Me coatings have very similar friction properties like hard metal free hydrogenated amorphous carbon (a-C:H) coatings. However, even optimized a-C:H:Me exhibits clearly higher wear rates and lower hardness values than a-C:H. The mainly used method to prepare a-C:H bases on a glow discharge in a hydrocarbon gas like acetylene or methane with a substrate electrode powered with radio frequency (r.f. - MHz range) or medium frequency (m.f. - some 10 to 100 kHz). To get more information on the effects of metal incorporation we exchanged the metal targets for graphite targets. The deposition experiments were carried out in an industrial scale d.c. magnetron sputter machine. To achieve an optimum adhesion of the coatings a metal based interlayer systems was deposited before starting the a-C:H growth. It was found that the metal free a-C:H coatings prepared with the reactive d.c. magnetron sputter technique had nearly the same composition and structure and also mechanical and tribological properties like a-C:H deposited by r.f. or m.f. processes. This was revealed by TEM, SIMS, Raman spectroscopy and by hardness and wear tests. Structure and morphology of a-C:H and a-C:H:Me coatings as well as possible reasons for the essential differences in the film properties will be discussed.
3:10 PM		D2-1-6 Microstructure and Properties of Diamond Like Carbon Films Deposited by Cathodic Arc Evaporation P.C. Tsai (National Huwei Institute of Technology, Taiwan, ROC); K.-H. Chen (Academia Sinica, Taiwan, ROC); C.M. Sung (KINIK Company, Taiwan, ROC) Diamond-like carbon films were deposited by cathodic arc evaporation process at substrate-bias voltage ranging from -50 to -300V. The characteristics of the films were investigated using Raman spectroscopy, x-ray photoelectron spectroscopy (XPS), atomic force microscope (AFM), nanoindentation tester and scratching tester. The Raman spectra showed that the wavenumber ranging from 900 to 1800 cm^-1 could be resolved into 1140 cm^-1, D band and G band. The sp³/sp² ratio of the deposited DLC films increased with the decreasing of I_D/I_G ratio. The XPS spectra data of the films etched by H⁺ plasma for varying time showed that there is an sp²-rich layer present at the surface of the films. The nanoindentation hardness increased with the increasing of maximum load. A 400 nm thick and well adhered DLC film was deposited on WC-Co substrate above a Ti interlayer. High-resolution transmission electron microscopy (HRTEM) studies on the films will also be discussed.
3:50 PM		D2-1-8 Substrate Geometry Effect on the Uniformity of Amorphous Carbon Films Deposited by Unbalanced Magnetron Sputtering X.-Z. Ding, X.T. Zeng (Singapore Institute of Manufacturing Technology, Singapore) An amorphous carbon (a-C) film was deposited by unbalanced magnetron sputtering technique. A special designed double-V shaped stainless steel model simulating a plastic injection mold gateway was used as the substrate in order to investigate the substrate geometric effect on the uniformity of the a-C film. The thickness, microstructure, and microhardness of the a-C film at different points of the substrate were measured by ball-crater, micro-Raman spectroscopy, and nanoindentation experiments, respectively. On the Raman spectra of the film, a broad asymmetric band in the wavenumber region of 1000-1800 cm^-1 was observed, which is a typical characteristic of the a-C films and can be commonly deconvoluted into Gaussian D (centered at approximately 1360 cm^-1) and G (centered at approximately 1580 cm^-1) sub-bands by curve fitting. It was found that, on both the bottom plane and sidewall parts of the double-V shaped substrate, the film thickness decreased and the intensity ratio of the two Raman sub-bands D over G increased with the increase of the geometric aspect ratio (R) of depth over width. On the sidewall parts of the double-V shaped substrate, the microhardness of the a-C film decreased significantly with the increase of the geometric aspect ratio R. On the bottom plane, however, the microhardness almost remained unchanged with the variation of the geometric aspect ratio. The influence of working atmosphere pressure and substrate bias on the film uniformity were also investigated.
4:10 PM		D2-1-9 Improved Adhesion of a-C:H Coatings by Defined Interlayer M. Weber, K. Bewilogua, A. Hieke, H. Thomsen, R. Wittorf (Fraunhofer Institute for Surface Engineering and Thin Films, Germany) Amorphous carbon (a-C:H) films respond very sensitive to local overload. E.g. in applications on forming tools, hard abrasive particles and high tension levels on the coating surface cause crack initiation and early coating failure. Compared to the high hardness, wear resistance and excellent friction properties, the adhesion of a-C:H films, measured with the scratch adhesion test, is relatively low. Crack initiation as a main mechanism of early coating failure could be simulated with a multi-scratch adhesion test. Overload resistance of a-C:H and a-C:H:Me films can be influenced in a wide range by the properties and the thickness of different interlayer systems. In this study comparatively thick metallic interlayers were combined with metallic nitride interlayers. Soft metallic interlayers can reduce internal stress, abate local overload and have to stop crack propagation. Likewise they determine the growth structure of the amorphous carbon top layer, which influences the crack growth noticeable. Hard metallic nitride interlayers, especially CrN, deposited at low temperatures in a PVD process have a supporting function and can improve the adhesion of a-C:H coatings supplementary. Additional gradient layers can act as a mediator between the different lattice structures of the interlayer system and the a-C:H top layer. Especially the influence of different a-C:H:Me layers on the adhesion of a-C:H top layers was investigated. Two well adapted multi-coating systems for high loaded tools and components will be presented. Application tests in metal forming have confirmed the good overload resistance of such multi-coating systems.