Development of energy efficient surfaces

Low emissivity coatings are one of the techniques used to reduce the heating and cooling costs of buildings. In this way, the energy used in buildings becomes more efficient and savings are achieved. In this thesis, it was tried to obtain an energy efficient surface by developing a dielectric/metal/dielectric structure on glass substrate. In addition to this structure, a barrier layer was also coated between the glass substrate and the structure to reduce the surface roughness and protect the structure. Firstly, designs were made using optical design program to determine the materials to be used. As a result of the design studies, Al2O3 material was preferred as the barrier layer, AZO was preferred as the dielectric layer and Ag was preferred as the metal layer. In order to determine the most suitable coating conditions, each layer was prepared at different pressures, different sputtering power and different thicknesses. The obtained results were analyzed and the most suitable parameters were determined. The appropriate thickness for Al2O3 was determined as 25 nm in the result of our previous studies, while the argon gas flow was determined as 5 sccm and the sputtering power was 150 W RF. The thicknesses for the AZO layer were determined as 10 nm for the lower AZO layer and 20 nm for the upper AZO layer, while the Argon gas flow was determined as 5 sccm and the sputtering power was determined as 100 W RF. For the Ag layer, firstly, 10 nm thick coatings with different gas flow values were made. Optimization studies continued for Argon gas flow values of 5 sccm, which gives the highest transmittance value in the visible region, and 50 sccm, which gives the lowest transmittance value in the infrared region. Coatings were made for different power values in the determined Argon gas flows and it was seen that 25 W DC power value gave the best result for both gas flow values. Afterwards, coatings of different thicknesses were made at 25 W DC power for both gas flow values. In Ag films prepared in different thicknesses, 5 nm thick continuous films could be obtained at 50 sccm gas flow, while the thinnest continuous film produced at 5 sccm gas flow was 7 nm thick. The prepared films were analyzed and it was seen that the energies of Ag atoms decreased in 50 sccm gas flow, and instead of preferring to grow with islands structure, the atoms spread more homogeneously on the surface and became thin films with less pores. As a result of the optical analysis, it was determined that the prepared AZO/Ag/AZO/Al2O3/Glass structure provided approximately 85% optical transmittance at 500 nm, and 79% and 84% reflectance values at 2.5 µm and 8 µm, respectively. The emissivity of this prepared structure was calculated as 0.055 by using the surface resistance value. This value was found to be competitive with commercial products. In addition, the fact that the stated results can be achieved with 5 nm thick Ag thin films further increases the value of the study.