ICMCTF2011 Session C1: Recent Advances in Optical Thin Films

Monday, May 2, 2011 10:00 AM in Room Sunset

Monday Morning

Start	Invited?	Item
10:00 AM		C1-1 Investigations of Diffusion Behaviour in Dielectric Coatings Justyna Kulczyk-Malecka, Peter Kelly, Glen West (Manchester Metropolitan University, UK); Gregory Clarke (Pilkington Technology Management, UK); Ivanka Iordanova (University of Sofia, Bulgaria); Vladimir Vishnyakov (Manchester Metroplitan University, UK) Multi-layer dielectric/silver/dielectric coating systems have excellent proprieties as heat insulators and for solar energy reflection and electrical conductivity. The largest scale market is dominated by low-emissivity (low-E) coatings, which are applied to large area architectural glazing to reduce heat losses from buildings. They combine high visible transparency with high reflectance in the far-infrared region, where the thin (~10nm) silver layer reflects long wavelength IR back into the building and the dielectric layers both protect the silver and act as anti-reflectance layers. In this study, a range of dielectric coatings have been deposited onto soda-lime glass substrates by reactive sputtering from metallic targets. The magnetron was driven in mid-frequency pulsed DC mode. Process variables investigated include operating pressure, oxygen flow rate and magnetron configuration. The as-deposited coatings were analyzed by micro Raman spectroscopy, X-ray diffraction (XRD) and scanning electron microscopy (SEM). Selected coatings were annealed at temperatures in the range 200-600^oC and re-analysed. The oxide samples were then over-coated with silver and annealed for a second time. These coatings were analysed by secondary ion mass spectroscopy (SIMS) and X-ray photoelectron spectroscopy (XPS) to determine the diffusion rates of silver and sodium (from the substrate) through the oxide coatings. The results to date, presented here, indicate that the structure of the coating, particularly the degree of crystallinity, has a greater impact on the diffusion of sodium through the coating than the diffusion of silver. Preliminary attempts have been made to estimate diffusion coefficients for these coating systems and to relate these values to processing conditions and the structural variations observed.
10:20 AM		C1-2 Electrochromic Performance of Hybrid Tungsten Oxide Films with Multiwalled-CNTs Additions Chung-Kwei Lin, Sheng-Chung Tseng, Chin-Hua Cheng, Chin-Yi Chen (Feng Chia University, Taiwan); Chien-Chon Chen (National United University, Taiwan) In this study, tungsten oxide films were prepared by sol-gel technique. Various amounts of multiwalled carbon nanotubes (MWCNTs) were added during sol gel process to obtain hybrid WO3/MWCNTs films. The original and hybrid films were characterized by thermogravimetric analysis, X-ray diffraction analysis, X-ray photoelectron spectroscopy and scanning electron microscopy analysis. While electrochromic performance was evaluated by potentiostat and UV-Visible spectroscopy. The influence on the structure and properties of tungsten oxide film due to MWCNTs addition were investigated. The results showed that all the films were amorphous and hybrid tungsten oxide films with 0.1wt% MWCNTs addition exhibited the best electrochromic performance.
10:40 AM	Invited	C1-3 Opto-Electronic Properties of Graphene Oxide Thin Films Manish Chhowalla (Rutgers University) In this presentation, a solution based method that allows uniform and controllable deposition of reduced graphene oxide thin films with thicknesses ranging from a single monolayer up to several layers over large areas will be described. The oxidation treatment during synthesis of GO creates sp³ C-O sites where oxygen atoms are bonded in the form of various functional groups. GO is therefore a two dimensional network of sp² and sp³ bonded atoms, in contrast to an ideal graphene sheet which consists of 100% sp² carbon atoms. This unique atomic and electronic structure of GO, consisting of variable sp²/sp³ fraction, opens up possibilities for new functionalities. The most notable difference between GO and mechanically exfoliated graphene is the opto-electronic properties arising from the presence of finite band gap. In particular, the photoluminescence can be tuned from blue to red to IR emission. The atomic and electronic structure along with tunable photoluminescence of graphene oxide at various degrees of reduction will be described.
11:20 AM		C1-6 Effect of Crystallinity and Oxygen Vacancy on Photocatalytic Properties of TiO₂ Thin Films Jing-Huei Huang, Ming-Show Wong (National Dong Hwa University, Taiwan) The effect of crystallinity and oxygen vacancy on photocatalytic properties of TiO₂ thin films was systematically studied. The films were prepared by argon–oxygen plasma using reactive sputtering with a titanium metal target and subsequently annealed at various temperatures of 400~800^oC in air, vacuum and H₂atmosphere. The results indicate that at the same temperature, the TiO₂ films annealed in H₂ achieve better crystallinity and generate more oxygen vacancies than the films annealed in air and in vacuum. In all the three annealing atmosphere, the higher the temperature is, the better the film crystallinity and the more the oxygen vacancies. Oxygen vacancies in TiO₂ film not only facilitate phase transformation but lower the band gap of TiO₂, and make the film visible-light responsive. Photocatalytic properties of the TiO₂ films were characterized in UV and visible light irradiation by following the Ag reduction and degradation of methylene blue. The films annealed at 600~700^oC in H_2, possess the best film crystallinity and proper concentration of oxygen vacancies and exhibit the best photocatalytic performance under both UV and visible light.
11:40 AM		C1-7 Structural and In-Depth Characterization of Variable Refractive Index Chromium-Silicon Mixed Oxides Produced by Reactive Ion Beam Mixing of the Cr/Si Interface Ramón Escobar Galindo, Lucía Vergara, Olga Sánchez (Instituto de Ciencia de Materiales de Madrid, Spain); Gonzalo Fuentes (Asociación Industria Navarra (AIN), Spain); David Duday (Centre de Recherche Public Gabriel Lippmann, Spain); Noelia Benito (Universidad Autónoma de Madrid, Spain); Nathalie Valle (Centre de Recherche Public Gabriel Lippmann, Spain); Víctor Joco, Carlos Palacio (Universidad Autónoma de Madrid, Spain); J.R. Rubio-Zuazo (SpLine, European Synchrotron Radiation Facility, France) The interest on mixed metal-silicon oxides includes their application, among others, as optical coatings with an adjustable refractive index. Chemical vapour deposition of these coatings is commonly used, although it frequently causes the undesirable incorporation of chlorine, hydrogen or carboxyl groups to the films. In this paper we report the formation of chromium and silicon mixed oxides using a novel alternative method. We induce the formation of mixed oxides from a sputter-deposited chromium film on a silicon substrate by reactive ion beam mixing bombarding the Cr/Si interface with oxygen. We have varied both the ion dose (from 1x10¹⁷ up to 1x10¹⁸ ions cm-²) and the implantation energy (40-100 keV) in order to modify the final composition of the coating. The composition profiles have been obtained by means of Rutherford backscattering spectrometry (RBS) with He ions at 3.035 MeV to make use of the resonance of alpha particles with oxygen at this specific energy. A more detailed analysis of the composition depth profiles was obtained by changing the He energy from 3.035 up to 3.105 MeV. Results have been compared with depth profiles obtained by secondary ion mass spectrometry (SIMS) and elastic recoil detection analysis using a time of flight station (ERDA-TOF) and by Monte Carlo TRIDYN simulations. X-ray photoelectron spectroscopy (XPS) depth profiles were carried out using a simultaneous Ar⁺ bombardment at low energy. Additional chemical state in-depth distributions were obtained by hard X-ray photoelectron spectroscopy (HAXPES) using synchrotron radiation and angle-resolved (ARXPS). Data obtained by ARXPS show that the Cr-O-Si system does not display preferential sputtering phenomena during Ar⁺ bombardment in depth profiling. X-ray diffraction (XRD) and scanning and transmission electron microscopy (SEM, TEM) assessed structural changes of the sample from polycrystalline to amorphous state upon increasing the implantation dose. We have determined how structural changes brought about by varying the ion beam implantation parameters are related to the optical properties of the coatings (mainly refractive index, extinction coefficient and reflectivity) as measured by spectroscopic ellipsometry and UV-VIS spectroscopy.