Papers

ICMCTF2006 Session C2/E6: Mechanical Properties of Optical Films

Monday, May 1, 2006 10:30 AM in Room California

Monday Morning

Start	Invited?	Item
10:30 AM		C2/E6-1 Adhesion Energy Measurement of Optical Thin Films: Can We Improve the Surface Mechanics of Multilayers? E. Barthel, E. Sondergard, D. Dalmas, M. Beauvais (CNRS/Saint-Gobain, France) On a constant move to improve performances, glass manufacturers like to tune the optical and IR reflection/transmission properties of their products by thin multilayer deposition. Besides optics, a secondary requirement is the mechanical response, which impacts decisively on product viability: in particular, good scratch resistance is necessary for both processability and reliability. However, a large number of parameters may govern the scratch resistance of coated systems. Both loading conditions and layer/substrate mechanical response must be taken into account. Based on recent models for the elastic contact of a coated substrate, we will explain why the interfaces dominate the scratch response of our typical thin films deposited on glass. Thus it is primarily the friction and the interfacial toughnesses which must be assessed and controled. While measuring the former is quite standard, one faces considerable difficulties in measuring the latter. For thin optical multilayers deposited on flat glass substrates, we have developed a wedge-loaded Double Cantilever Beam technique which allows well defined toughness measurements. We will present in details our results on silver-based multilayers and show how they correlate to the interfacial structure within the multilayers. Finally, future directions in understanding the scratch resistance of these systems will be discussed.
11:10 AM		C2/E6-3 Chemomechanical Effects in Optical Coating Systems K.J. Belde, S.J. Bull (University of Newcastle, United Kingdom) The major in-service failure mechanisms of modern optical coatings for architectural glass can be mechanical (e.g. scratch damage). Many of these coatings are multilayer structures of less than 100nm thickness and different coating architectures are possible (i.e. different layer materials, thickness and stacking order). These coatings are exposed to different types of climatic conditions. One of the effects that might weaken the strength of these coatings may be due to interaction with water and this is termed the chemomechanical effect. It has been shown that the chemomechanical effects have a considerable effect on the hardness as well as the fracture resistance of oxides. High performance glass is coated with anti-reflection coatings (e.g. ZnO, SnO₂) and barrier layers (e.g. TiOxNy) which are expected to suffer from such chemomechanical effects. In the case of solar control coatings these coatings are often on the inside of double glazing units to protect them from the environment, but in the case of optical lenses and other similar cases the coatings are exposed to the environment. In this study we have investigated the chemomechanical behaviour of a range of optical coatings exposed to water. Water exposure tends to reduce the hardness and increase the fracture resistance of the coating making it more vulnerable to plastic deformation during scratching. The susceptibility of different coatings to chemomechanical effects will be discussed.
11:30 AM		C2/E6-4 Optically Transparent Hard Coatings Consisting of Al-Si-N A. Pelisson, F.-J. Haug, M. Parlinska-Wojtan, J. Patscheider (EMPA, Switzerland) Thin films consisting of Al-Si-N were deposited by DC magnetron sputtering at 200°C and characterized by XRD, XPS, EPMA, TEM and nanoindentation. Under conditions of sufficient nitridation densely packed optically transparent coatings were obtained. They consist of nanocrystalline AlN with silicon nitride. Analysis of the lattice parameter provided evidence that silicon is substitutionally incorporated in the lattice of h-AlN. The solubility limit at the deposition temperature lies, in contrast to published values above 12 at% silicon. The incorporation of Si in the layers causes an abrupt change of the preferred orientation. The hardness of these films shows a weak maximum around 25 GPa. The combination of appreciable hardness with optical transparency, along with low deposition temperature, makes this type of films interesting for wear protective applications on a variety of surfaces requiring optical transparency or specific interference coloring.
11:50 AM		C2/E6-5 Property Changes in Decorative TiC_xO_y Thin Films: Effect of the O/Ti Ratio A.C. Fernandes, F. Vaz (Universidade do Minho, Portugal); Ph. Goudeau, E.Le Bourhis, J.P. Rivère (Universitat de Poitiers, France); N.M.G. Parreira (ICEMS - University of Coimbra, Portugal); N. Martin, J.M. Chappe (Ecole Nationale Supérieure de Mécanique et des Microtechniques, France) Within the frame of this work, coloured titanium oxycarbide, TiC_xO_y, films were prepared. The presence of the oxygen allows tailoring the film properties between those of titanium carbide and those of the correspondent titanium oxide. Varying the oxide/carbide ratio allowed tuning the band-gap, bandwidth, and crystallographic order between oxide and carbide and consequently electronic, mechanical and optical properties of the material. Films were deposited on steel, silicon and glass substrates at various temperatures by dc reactive magnetron sputtering. Two different sets of samples were prepared from a Ti target with some C pieces, varying the oxygen flow and the bias voltage applied to the substrate. The evolution of the different elements concentration with the oxygen flow can be divided into 3 different regimes i) carbide, ii) a transition zone and iii) an oxide one, with clear influence on the films structure and morphology evolution. The structure of the films, determined by X-ray diffraction (XRD), strongly influenced the overall film properties, namely electrical ones such as resistivity and optical including colour and reflectivity. Fourier transformed infrared spectroscopy (FTIR) and spectroscopic ellipsometry (SE) were used to further confirm the different nature of films structure/bond characteristics, and thus to better understand its property variations. Thermal stability of the films was tested in vacuum in the temperature range [400 - 800 °C]. Biased and low oxygen content samples showed no significant changes in hardness after thermal annealing. Significant property changes were observed for samples prepared with the highest oxygen flows.
12:10 PM		C2/E6-6 TiC_xO_y Thin Films for Decorative Applications: Tribocorrosion Mechanisms L.A. Rocha, M.T. Mathew, E. Ariza, F. Vaz, A.C. Fernandes, L. Cunha, P. Carvalho, L. Rebouta, E. Alves (Universidade do Minho, Portugal); Ph. Goudeau, J.P. Rivère (Universitat de Poitiers, France) The main aim of this work is the investigation of the tribocorrosion behaviour of single layered zirconium oxynitride, ZrN_xO_y, thin films in alternative linear regime of sliding and immersed in an artificial sweat solution at room temperature. The films were produced by dc reactive magnetron sputtering, using a pure Zr target. In order to get different ratios of oxygen and nitrogen in the films, the flow rate of reactive gases (a mixture of oxygen and nitrogen) was varied. The control of the amount of oxygen allowed the film properties to be tailored from those of metallic zirconium nitride to those of the correspondent oxide. During the wear test both the open circuit potential and the corrosion current were monitored. Also, Electrochemical Impedance Spectroscopy (EIS) tests were performed before and after sliding in order to evaluate, in detail, the modification of the protective character of the coating introduced by the joint action of wear and corrosion. The modifications of the coating microstructure and/or chemical composition induced by the variation of the deposition parameters was also evaluated and correlated with the wear-corrosion mechanisms occurring in each system.