Preparation And Performance Of Si_1-xAl_xN/Ag/Ta Low-E Films

Environmental pollution and energy crisis are two problems of sustainabledevelopment in the21thcentury. With the process of accelerated urbanization, buildingenergy consumption will sustained growth, using the eco-friendly and energy-efficientlow-emissivity films has becoming hot-debated issues in recent years. The developmentof new low-emissivity films with high transmittance in the visible light region, highreflectivity in the infrared region and long service life from the structural andcomponential improvements are the key points. The main challenges are:(1)Developfacile and general methods to prepare low cost of low-emissivity films with novelstructures for excellent low-emissivity performance;(2)Study the structural andcomponential factors on low-emissivity performance.The object of the dissertation is set to partly solve the limitations in the presentlow-emissivity films research area, for which Si1-xAlxN/Ag/Ta sandwiching structurelow-emissivity (Low-E) films were prepared by radio frequency reactive magnetronsputtering (RF-MS) on glass substrates. The morphology, chemical state andperformance of the film system were characterized by Surface Profilometer, dual beamfocused ion beam-scanning electron microscope, UV-Vis spectrophotometer, X-rayphotoelectron spectroscopy, four-point probe meter, Fourier-transform infraredspectroscopy and electrochemical workstation. The visible light transmittance, infraredreflectivity, surface morphology and microstructure, chemical components and chemicalstate, and the corrosion resistance of low-emissivity films were studied systematically.The main innovations and results are as follows:In this work, we found that adding a1.2nm Ta seeding layer causes a significantdecrease in the roughness of Ag films(from1.95nm to1.24nm) and reduces theminimum film thickness required to obtain a continuous layer, indicating an effectivemethod for depositing smooth Ag films on glass substrates employing a thin nucleationlayer of deposited Ta for improved nucleation of the Ag films deposited.The depositedAg films exhibit smaller sheet resistance in comparison to those of Ag films directlydeposited on glass substrates. The sheet resistance has been reduced from9.5□-1for apure Ag film to5.2□-1for Ag/Ta films. Ta is deposited on a glass substrate as aseeding layer for the two-dimensional growth of Ag thin films because Ta has goodthermal stability and can induce a negative surface-energy change in Ag/glass. Using classical oxides as dielectric is quite difficult because the Ag film would beoxidized during the dielectric deposition in O2reactive atmosphere. A novel nitridedielectric Si1-xAlxN solves the problem. In this study, the optical properties, as well asphysical and chemical states of Si1-xAlxN coatings were also investigated. The resultsshowed that the Si1-xAlxN films exhibit an excellent visible light transmittance(T%=90.2%at λ=550nm). Furthermore, the61nm Si1-xAlxN dielectric-layer could notonly increase transmittance in the visible light range of Ag film based on ananti-reflection effect, but also modify the intrinsic color of Ag film from sapphire tototal color neutrality，this fact has a relevant effect on the internal visual comfort as wellas the external appearance of a building.The corrosion behavior of the Si1-xAlxN coatings was investigated usingpotentiodynamic polarization measurements in a conventional three-electrode cellemploying an electrochemical workstation. The electrochemical measurements wereperformed in a3.5wt%Na2S2O3solutions. The results indicate the Si1-xAlxN coatingsimproved corrosion resistance of the coated system. The corrosion current density (icorr)decreases about one or two orders of magnitude.The results showed that the Si1-xAlxN/Ag/Ta low-emissivity films exhibit anexcellent visible light transmittance (T%>82%) and remarkable high infraredreflectivity (R%>94%in the2.5~25μm range). In principle, compared with the existinglow-emissivity films，the approach to obtain Si1-xAlxN/Ag/Ta sandwich structure in ourwork could provide an alternative way to fabricate outstanding low-emissivity filmswhich have a high performance-price ratio.All these studies could provide the exploration and accumulation for thedevelopment and application of low-emissivity films, further to put up the importanttheories and directions for the relative research fields.