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    High optical response NiO, Pd/NiO and Pd/WO3 hydrogen sensors
    (Pergamon-Elsevier Science Ltd, 2022) Coban, Omer; Tekmen, Suleyman; Gur, Emre; Tuzemen, Sebahattin
    In this study, NiO and WO3 oxide semiconductors were fabricated on glass substrates by RF Magnetron Sputtering technique. Structural and optical characterizations of the semiconductors were performed using XRD, SEM, and optical absorption measurements. NiO and WO3 thin films were occasionally coated with palladium. In order to investigate the optical response of these semiconductors under hydrogen gas exposure, an optical gas sensor test system was installed and programmed. In both of the coated and uncoated cases, optical absorption changes due to hydrogen gas exposure on the surface were investigated. It was observed that these changes occur between 450 and 850 nm wave lengths range. The absorption in the NiO semiconductor was reduced between these wave lengths, while the absorption was increased in the WO3 semiconductor. In the uncoated state, only NiO gave an optical response to hydrogen gas. While the palladium coated NiO (Pd/NiO) sensor had the best response and recovery times of respectively 70 s and 206 s for 2% fraction of H-2 gas at 300 degrees C constant temperature, the Pd/WO3 sensor gave the best response time of 340 s. Palladium coating resulted in approximately 150% increase in the responses of the NiO sensors at higher H-2 concentration. The lower limit of H-2 sensing of the Pd/NiO sensors at 300 degrees C was at the H-2 fraction of 0.05%, while for Pd/WO3 sensors this value was 0.025%. (C) 2022 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.
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    Photoluminescence and structural properties of zirconium dioxide thin films produced by RF sputtering technique
    (Springer, 2021) Bakacak, Pinar K.; Gur, Emre; Bayram, Ozkan; Tuzemen, Sebahattin; Simsek, Onder
    In this study, Zirconium Oxide (ZrO2) thin films were produced by using radio frequency magnetron sputtering method on glass substrate at various pressures. The effects of growth pressure on the characteristics of grown Zirconia nanostructures were investigated by Atomic Force Microscopy (AFM), Scanning Electron Microscopy (SEM), X-Ray Diffraction (XRD), Uv-Visible Spectroscopy and Photoluminescence Spectrometry (PL). XRD analysis showed that peaks of the monoclinic and tetragonal phases were more effective at low growth pressure, but different monoclinic phase peaks were present at increasing growth pressures. The surface morphological properties of the films such as average and maximum roughness, changed significantly with increasing growth pressure, and the maximum peak height first increased to 40 nm and then decreased to 20 nm. The optical transmittance of these thin films was examined in the 450-1100 nm wavelength range, covering both the visible and near-infrared spectral range, and it was found to be approximately 95% at 550 nm wavelength, and the optical band gaps were calculated to be approximately 3.26 eV by PL analyses. Uv-Visible spectroscopy analysis showed that the refractive index of the Zirconia films decreases from 2.09 to 1.79 with increasing wavelength of the incident photon. ZrO2 thin films are considered potential materials for transparent electronic devices because of their high transmittance value.