ICMCTF2003 Session C2/E6: Mechanical Characteristics of Optical Coatings

Wednesday, April 30, 2003 8:30 AM in Room California

Wednesday Morning

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8:30 AM C2/E6-1 Mechanical Characteristics of Optical Coatings Prepared by Different Techniques: A Round Robin Study
J.E. Klemberg-Sapieha, J. Oberste-Berghaus, L. Martinu (École Polytechique de Montréal, Canada); R. Blacker (Veeco Instruments Inc.); P. Martin (CSIRO, Australia); S. McEldowney (JDSU/OCLI); I. Stevenson (Denton Vacuum LLC)
Good performance of optical coatings depends on a suitable combination of optical and mechanical properties. Therefore, successful applications require good understanding of the relationship between the optical, microstructural and mechanical characteristics, and the film stability. In addition, there is a lack of standard mechanical tests which allow one to compare film properties measured in different laboratories. In this work, we give an overview of a methodology of mechanical measurements suitable for optical coatings; this includes depth-sensing indentation, scratch resistance, friction, abrasion and wear testing, and stress and adhesion evaluation. The above techniques are applied here to systematically compare the mechanical behavior of high and low index materials, namely TiO2, Ta2O5 and SiO2, prepared by different complementary techniques. These techniques are magnetron sputtering, ion assisted electron beam evaporation, dual ion beam sputtering, filtered cathodic arc deposition and plasma enhanced chemical vapor deposition. The mechanical properties will be correlated with the film microstructure inherently related to the energetic conditions during the film growth.
9:10 AM C2/E6-3 Improved Mechanical Properties of Optical Coatings via an Enhanced Sputtering Process
G.T. West, P.J. Kelly (University of Salford, United Kingdom)
Magnetron sputtering is the process of choice for the deposition of a wide range of industrially important coatings. However, current processes have inherent limitations in terms of controlling the flux and energy of particles incident at the substrate at each stage of the deposition process. Consequently, film properties may not be optimal. In order to overcome this limitation, studies are being made of an enhanced sputtering system, which incorporates a gridless linear ion source suitable for use in a reactive gas environment. The impact of this source on the structure and properties of dielectric coatings, in comparison with films grown in a standard system, is reported here. Coatings have been characterised in terms of their structures, optical and mechanical properties using a range of techniques, including SEM, AFM, XRD, spectrophotometry, scratch adhesion and wear testing. Results to date demonstrate that the enhanced system improves the flexibility of control of the growth parameters in a magnetron sputtering system.
9:30 AM C2/E6-4 Mechanical Modelling of Multilayer Optical Coatings
E.R. Gutierrez-Berasategui, S.J. Bull, T.F. Page (University of Newcastle, United Kingdom)
Modern optical coatings, such as solar control coatings, are usually designed based on their optical properties but the major failure mechanisms can be mechanical in some applications (e.g. scratch damage). Many of these coatings are multilayer structures and many different coating architectures are possible (i.e.different layer materials, thicknesses and stacking orders). Testing all possible combinations is expensive and time consuming and thus there is a need for a modelling approach which can be used to predict the mechanical behaviour of any proposed coating design. Using nanoindentation techniques the hardness behaviour of coated glass can be determined provided that the coating layers are not too thin. Data generated by this approach can be used in modelling the hardness of a multilayer coating; a predictive model based on the work of indentation approach has been developed and tested for a range of coatings on glass. This paper will introduce the successful application of the model to a multilayer optical coating stack and highlight areas where the model needs to be improved in order that the model output better matches experimental data.
9:50 AM C2/E6-5 Reactive Sputtering of Nanostructured Titanium and Chromium Oxide Films
M.S. Wong, C.L. Lin, T.S. Yang (National Dong Hwa University, Taiwan, ROC); M.E. Graham (Northwestern University)
The outstanding properties of titanium and chromium oxides have made them useful for many applications. Ion-assisted, high-rate, reactive dc magnetron sputtering is used to deposit the nanostructured oxide films. Various characterization methods such as ellipsometry, Raman spectroscopy, XRD, SEM, hardness and stress measurement techniques were used to measure crystallinity, morphology, optical and mechanical properties of the films. Depending on the growth parameters, oxides of various compositions were detected in the preparation of the oxide films. Under suitable conditions, the sputtered Ti atoms will react with the partial pressure of supplied oxygen to form stoichiometric films of colorless TiO2. The transparent films are of the rutile, anatase or mixed crystal forms depending on growth conditions. The rutile phase has a higher refractive index (up to 2.7) and a higher hardness (15-20 GPa) than the anatase phase, but it is the anatase that show the stronger photocatalytic effect. Increasing substrate bias, increases the hardness and the stress in the film and reduces the value of the refractive index. The effect of the addition of chromium oxide into titanium oxide and the effect of nanolayer structure on the formation of oxide phases will also be reported.
10:10 AM C2/E6-6 The Characteristics of Aluminum-doped Zinc Oxide Films Prepared by Pulsed Magnetron Sputtering from Powder Targets
Y. Zhou, P.J. Kelly, A. Postill (University of Salford, United Kingdom); O.A. Abu-Zeid, A.A. Alnajjar (UAE University, UAE)
Mixed zinc oxide and alumina powder targets have been used to prepare transparent semi-conductive films on glass by pulsed magnetron sputtering. The structure, crystallinity, optical properties, electrical properties and adhesion of the films were investigated using a range of techniques, including SEM, XRD, spectrophotometry, surface profilometry, four-point probes and scratch adhesion testing, and the findings are described in this paper. Also, the properties of the coatings before and after annealing under various conditions are compared. The crystallinity of the films increased dramatically and the preferred orientation of the crystal changed thoroughly from (100) to (002) after annealing. The transparency of the coatings, especially over the wavelength range 400 to 500 nm, was improved, with the average transparency within the whole visible range being up to 90%. Resistivities as low as 4E-3 Ohm.cm were obtained after annealing, without deterioration of the coating-to-substrate adhesion. The results to date demonstrate that the pulsed magnetron sputtering of Al-doped ZnO films from powder targets is a versatile, novel technique for the deposition of high quality TCO materials.
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