"Active" Optical Films
Monday, April 10, 2000 12:30 PM in Room Sunset
C1-7 Smart Switchable Coatings for Glaxzng and Information Display Applications
C.M. C.M. Lampert (Star Science)
Switchable coatings can make a glazing switch dynamically with lighting or comfort needs. Typical switchable glazing can change from 70% to at least 20% visible transmittance. Some switching technologies can darken down to as low as 1% transmittance. Also, switchable coatings can be used to display large-area information. Low-cost banner displays or page size electronic paper displays have been demonstrated. The coatings that make up these switchable technologies can have a range of adjustable absorption properties or contrast ratios. For glazing application they offer adjustable shading coefficients which can benefit aircraft, automotive and building windows. Other products include switchable modulators, mirrors, and eyeglasses. A discussion of technologies covering electrochromism, suspended particles, dispersed electrophoresis and encapsulated liquid crystals will be made with up-to-date progress in these fields. Electrochromism involves the reversible intercalation of ions and electrons into a compound causing absorption centers to form. Suspended particles, electrophoresis and encapsulated liquid crystals use a field effect to make absorption or reflectance changes in the medium. The comparative properties and characteristics of these various switching technologies are discussed. Several examples of current technology are taken from selected companies. Key patents and deposition techniques to fabricate devices are discussed. Open issues concerning coating properties and necessary improvements are covered.
C1-9 Optical Properties of Zinc Oxide Films Containing Gold or Ruthenium Colloids
B.J. Bozlee (University of Great Falls); G.J. Exarhos (Pacific Northwest National Laboratory)
Gold and Ruthenium colloids have been incorporated into thin films of ZnO by spin coating metal ion-doped solutions of zinc acetylacetonate onto quartz, Pt, or Si substrates, followed by heating at 400 oC. Both colloid-containing films exhibit a blue tint due to Mie light absorption of the metal nanoparticles. Analysis of the visible absorption spectra of gold colloids suggests particle radii on the order of 2 nm. However, electron microscopy reveals some larger particles and particle aggregates as well. While the Au colloid absorption resonance is observed at ~575 nm, excitation profiles determined from Raman scattering measurements of the colloidal films exhibit red-shifted maxima near 700 nm. We attribute this striking scattering enhancement for excitation wavelengths near 700 nm to localized Surface-Enhanced Raman (SER) scattering of the E1 longitudinal optic mode of the ZnO matrix near Au particle aggregates. Ru colloids also induce SER scattering from residual ruthenium dioxide which apparently coats the Ru metal particles. In this case, the SER scattering appears to be at a maximum when the laser excitation is tuned into the maximum of the Ru colloid absorption band, in accord with the so-called electromagnetic theory of SER scattering. While not all of the ruthenium in Ru:ZnO appears to be in the zero oxidation state, XPS measurements show that only fully reduced gold is present in Au:ZnO films. Potential uses of such films for sensor or in non-linear optic applications will be discussed.
C1-10 Optical Properties of Li@super +@ Doped Electrochromic WO@sub 3@ Thin Films
I. Porqueras, E. Pascual, E. Bertran (Universitat de Barcelona, Spain)
As a component part of an electrochromic device, WO@sub 3@ layers are understood to be the main responsible of the color change of this devices when cationic ions are inserted in its crystalline lattice. In the search of a suitable all solid electrochromic device, the light should be inserted into the structure in one run process. In this work Li@super +@ ions were incorporated on the WO@sub 3@ layer from a gas phase during the deposition process.@paragraph@ Electrochromic WO@sub 3@ thin films were deposited on fused silica and silicon substrates by physical vapor deposition techniques. The substrate temperature during the WO@sub 3@ deposition process was kept at 150ºC and the oxygen pressure was 5·10@super –4@mbar. In order to improve the performance of this one run doping method series of samples, with Li to W atomic ratio ranging from 0 to 0.4, were prepared to study the effect of the Li content on the optical properties of the WO@sub 3@ thin films.@paragraph@A complete optical characterization in the ultra violet, visible and infrared range was carried out using ultra violet–visible transmittance, ultra violet–visible multichannel spectroscopic ellipsometry and FTIR spectroscopy. A clear dependence of the optical properties on the level of Li was observed. It was also analyzed the atmospheric evolution of the optical properties for a sample with an specific Li to W ratio.@paragraph@ These results are a first step to achieve a better understanding of some problems related to the doping of the electrochromic layers with lithium ions, such as irreversibility, stoichiometry effects, correlation between optical an electrical properties and optical absorption modeling.
C1-11 Transparent Conducting Oxide Thin Films Prepared on Sapphire by Magnetron Sputtering
T. Miyata, T. Yamamoto, Y. Toda, T. Minami (Kanazawa Institute of Technology, Japan)
For the purpose of fabricating light emitting devices on sapphire substrates, we have used magnetron sputtering to prepare transparent conducting oxide (TCO) thin films on various sapphire surfaces. In addition, the suitability of devices prepared with these TCO films was investigated. Various TCO films such as impurity-doped ZnO, In@sub 2@O@sub 3@, and SnO@sub 2@ as well as multicomponent oxides composed of combinations of these oxides were deposited by dc magnetron sputtering on sapphire (Al@sub 2@O@sub 3@) surfaces cut to different crystallographic orientations. The sputter deposition was carried out at pressures of 0.2 to 1.2 Pa in pure Ar gas or a mixture of Ar and O@sub 2@ gases. The substrate temperature was varied from room temperature to 350@super o@C. As an example, we found that the electrical properties of Al-doped ZnO (AZO) films were strongly dependent on the orientation of the Al@sub 2@O@sub 3@ crystalline structure at the surface used. A lower resistivity was obtained in epitaxial AZO films deposited on an a-axis Al@sub 2@O@sub 3@ surface; i.e., the crystallinity of these AZO films was better than that of films deposited on other surfaces. In addition, the substrate temperature dependence of electrical properties in AZO films was significantly affected by the content of Al doped into AZO films. The stability of electrical properties in various atmospheres was evaluated for various TCO films deposited on the different Al@sub 2@O@sub 3@ surfaces. Epitaxial TCO films deposited on Al@sub 2@O@sub 3@ were found to be more stable in air than TCO films deposited on glass substrates.
C1-12 Effect of Process Parameters and Properties for Low Resistivity Indium-tin Oxide Thin Films
C.-Y. Chen (Wintek Corporation, Taiwan ,Republic of China); J.-Y. Yew (Wintek Corporation, Taiwain, Republic of China); J.-M. Ni (Wintek Corporation, Taiwan, Republic of China)
Indium-tin oxide (ITO) films have been deposited onto sodalime glass substrate by DC magnetron sputtering with ceramic ITO targets. The effect of process parameters on the properties of low resistivity and high transmittance indium-tin oxide thin films have been investigated. The influence of the dynamics deposited rate, oxygen flow rate and substrate temperature during sputtering process for the growth and morphology of indium-tin oxide thin films must be considered. For the ITO film properties , the thickness of the ITO film is shown a considerable impact on the sheet resistance and the optical transmittance. Additionally, the uniformity of ITO film and adhesion and the other optical properties also are the main focus. The relationship between electrical, optical properties and microstructure of indium-tin oxide thin films have been investigated by using four-point probe, spectrophotometer, scanning electron microscope and X-ray diffractometer.