Papers

AVS1996 Session VM-TuA: Tailored Multifunctionality in Thin Films

Tuesday, October 15, 1996 2:00 PM in Room 104A/B

Tuesday Afternoon

Start	Invited?	Item
2:00 PM		VM-TuA-1 Multifunctional Multilayer Optical Coatings P. Martin, J. Johnston, W. Bennett, J. Affinito (Pacific Northwest National Laboratory) Multilayer optical coatings have been developed which heated and defogged the substrate, provided abrasion resistance, and controlled emittance. All coatings were deposited by reactive dc and rf magnetron sputtering. Substrate sizes ranged from 2.5 cm to 2 m in diameter. A seven-layer SiO\sub 2\/ Al\sub 2\O\sub 3\/ Ta\sub 2\O\sub 5\/Au antireflection coating was applied to 28 cm diameter LIDAR (laser radar) windows. This coating was very effective at deicing and defogging the windows, and provided abrasion resistance during cleaning. The average visible reflectance of the windows with both sides coated was less than 1%. Seventeen-layer SiO\sub 2\/ Si\sub 3\N\sub 4\/ TiO\sub 2\/ Ag coatings were applied to video camera lenses to reject at least two laser wavelengths, defog the lens, and provide a high transmission notch at the operating wavelengths. These coatings contained up to two metal layers, which provided the required current carrying capabilities. The coatings were able to heat the substrates at a rate of 16 degrees C per min at relatively modest power inputs of 2 W/cm\super 2\. The third coating was a SiO\sub 2\/Al\sub 2\O\sub 3\/ZrN solar reflector for space structures, which minimized the solar absorption of the ZrN layer and tuned the IR emittance for high heat radiation. The room temperature emittance of these coatings was greater than 0.3. Replacement of the oxide dielectric layers with vacuum-deposited polymer layers will be discussed, and polymer designs presented.
2:20 PM		VM-TuA-2 Epitaxial Ruby as a Thin-film Sensor D. Clarke (University of California, Santa Barbara) The photoluminescence from Cr ions substituting on the Al sub-lattice of sapphire provides the physical basis for a non-contact sensor based on shifts in the emission and absorption spectrum of sapphire. We have been exploiting the ruby photoluminescence as a means of probing the local strain, temperature and physical damage in thin films of ruby grown epitaxially on sapphire substrates. The fabrication of ruby thin-film sensors of varying configurations will be described together with their implementation for real-time sensing with a spatial resolution approaching one micron.
3:00 PM		VM-TuA-4 Post-deposition Processing of Sputtered and Solution-derived Conducting and Transparent Oxide Films G. Exarhos, C. Windisch (Pacific Northwest National Laboratory); S. Sharma (University of Hawaii) Electronic conductivity in wide band-gap semiconductors typified by ZnO is associated with donor states within the bandgap created by an attendant non- stoichiometry or by tri-valent cation (Al/super +3/, Ga/super +3/) dopant introduction. Associated with this conductivity is an increase in infrared reflectivity which results from free carrier absorption. While conducting films can be prepared through careful selection of parameters during sputter deposition or control of the resident chemistry during solution deposition, post deposition processing also can be used to enhance conductivity. When subjected to electrochemical cathodic reduction in a nonaqueous solvent, resistive sputter deposited films on Si show at least a six order of magnitude increase in conductivity. Enhanced conductivity also is registered in films subjected to post deposition annealing in hydrogen. The defect states in such films are characterized non-destructively by transmission-reflection spectroscopy, and on a molecular level by means of laser Raman spectroscopy. Both the E/sub 1/:E/sub 2/ and 2LO:E/sub 2/ mode intensity ratios were found to increase with film defect content. Changes in the Raman spectrum are correlated with defect content, film resistivity, and infrared reflectivity.
3:20 PM		VM-TuA-5 Epitaxial Growth of ZnO Thin Films on R-plane Sapphire Substrate by rf Magnetron Sputtering Y. Kim (Kyonggi University, Korea); H. Yang, J. Park, J. Han (Korea Electronic Technology Institute); Y. Lee, H. Kim (Seoul National University, Korea) ZnO thin films were deposited on R-plane sapphire substrate. The effects of the thermal energy and the kinetic energy of the sputtered species on the growth of ZnO thin films were studied. Increasing the substrate temperature at low chamber pressure, ZnO structure were changed from c-axis preferred oreinted polycrystalline to (110) epitaxial thin films because of the enough thermal energy and extra kinetic energy of the sputtered species for epitaxial growing. Increasing chamber pressure at the same temperature c-axis preferred oriented texture were grown due to the kinetic energy loss by scattering. ZnO structure was also affected by rf power. Increasing rf power, high quality ZnO thin films were grown. But to high rf power deteriorate the structural properties due to the extra high kinetic energy in addition to the thermal energy. High quality (110) ZnO epitaxial thin films were grown under the condition of 400/supero/C, 250W, and 5mTorr. According to the RHEED and TEM observation, there was no double diffraction distortion and any other patterns.
4:20 PM		VM-TuA-8 Dependence of Microstructure and Thermochromism on Substrate Temperature for Sputter-deposited VO\sub 2\ Epitaxial Films P. Jin, K. Yoshimura, S. Tanemura (National Industrial Research Institute of Nagoya, Japan) Vanadium dioxide (VO2) exhibits thermochromism via a reversible semiconductor-to-metal phase transition at around 68C. Thin films of VO2 have been studied for optical switching devices and advanced window coatings. While in most cases the VO2 films were deposited with a polycrystalline feature, it is necessary to obtain single crystalline films for the best understanding of this promising material. Thin films of VO2, approximate 100nm in thickness, were deposited on substrates of sapphire, Si and glass by reactive magnetron sputtering. Structural characterization was done with XRD, RHEED, AFM and TEM. Heteroepitaxy of VO2 on sapphire was obtained at substrate temperatures (Ts) above 300C with precise control of the deposition parameters. Epitaxial relationship between the film and sapphire was discussed. The morphology and its Ts dependance for the epitaxial films were studied in detail with AFM. The thermochromism of the epitaxial films depends strongly on deposition temperature. The change in resistivity upon phase transition varies from 2 orders of magnitude for Ts=300C and more than 4 orders of magnitude for Ts=500C. Furthermore, all the epitaxial films have significantly reduced transition temperatures with the lowest one of 45C for Ts=300C.
4:40 PM		VM-TuA-9 Magnetron Sputtering Deposition of Li-Compound Thin Films G. Thompson, D. Allred, P. Brovkin (Brigham Young University) We report the preparation and optical characterization of Li- compound thin films (LiH, LiF). These, due to their low absorption, may have a role as spacer layers in x-ray multilayer reflectors. The rock salt structure of the Li-compound film could allow for the development of a crystalline based multilayer. Crystalline based multilayers have been prepared for Josephson junction studies and hardness coatings. Each of these applications have shown that such a structure, if grown epitaxially, have atomicly abrupt interfaces. Crystalline based multilayers have generally been ignored in soft x- ray mirrors because of their low theortical reflectance. However, some nitride based crystalline structures paired with a suitable spacer layer (like the Li-compounds) could generate respectible reflectance. Unfortuanately, the Li-compound structures produced in our work showed extremely rough surface morphology by SEM. Chemical analysis of the thin films were done through comparing band gap energies by UV fluorescence. Experimental results of film growth will be discussed.