Porosity Evaluation of TiO2 Thin Films Deposited Using Pulsed DC-magnetron Sputtering
Keywords:pulsed dc-magnetron sputtering, TiO2 thin films, titanium oxide, optical constants, bias voltage, porosity
Titanium oxide (TiO2) thin films (1 μm – 4 μm thickness) were deposited on porous Hastelloy-X substrates using pulse dc-magnetron sputtering. The optimal discharge power (400 W), distance between magnetron Ti cathode and substrate (3 cm) were estimated experimentally. When the discharge power, distance between magnetron and substrate was kept constant (optimal), other technological parameters such as bias voltage and oxygen partial pressure were changed to produce higher density films. The optical, structural properties, densification process and porosity of titanium oxide (TiO2) thin films were investigated. The crystal phase, crystallite size and micro stresses of formed TiO2 thin films were estimated from XRD measurements. The surface microstructure and the cross section were investigated with SEM. The optical properties were analyzed with ellipsometer (632.8 nm) and the porosity was estimated from the varied values of refractive index. The results show that refractive index changes slightly (from 2.84 to 2.75) with increase of the oxygen partial pressure from 1.3 Pa to 5.9 Pa and formed TiO2 thin films start to be denser. The growth rate of thin films decreases nearly 15 % with adding the bias voltage to the substrate during the deposition. The refractive index changes from 2.80 to 2.51 with increase of bias voltage from 0 V to –150 V, and the deposited thin films start to be denser, also. Experimental results showed that formation of pure titanium oxide thin films were observed in all experimental cases. Only crystallite sizes and orientation were changed.
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