Synthesis and characterization of nio thin films and nanostructures for gas sensing applications

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dc.contributor.authorMkwae, P. S.
dc.date.accessioned2023-03-14T10:35:07Z
dc.date.available2023-03-14T10:35:07Z
dc.date.issued2019
dc.descriptionA dissertation submitted in fulfillment of the academic requirements for the degree of Master of Science in the Department of Physics in the Faculty of Science, Agriculture and Engineering, University of Zululand, 2020en_US
dc.description.abstractNiO thin films were deposited at different temperatures (RT, 100 °C, 200 °C, 350 °C and 450 °C) using a direct current (DC) magnetron sputtering system and then nickel oxide nano structures were subsequently synthesized on the deposited NiO film using the hydrothermal method. The thin films and nanostructures were subjected to various characterisation techniques (x-ray diffraction, Rutherford Backscattering Spectroscope, Raman, UV-Visible, Scanning Electron Microscope, x-ray Photoelectrons Spectrometre) before testing their gas sensing properties. The thin films deposited were found to be non-crystalline containing amorphous phases. The deposition temperature was found to have no effect on the film thickness, since all films deposited at different temperatures were found to have the same thickness of 25 nm, with uniform distribution of particles on the surface, as observed on the Scanning electron microscope (SEM). These NiO thin films were deposited for a duration of 45 minutes. XPS was used to investigate the presence of Nickel and Oxygen and their oxidation states in as-deposited samples. Gas sensing properties of NiO films and nano-structures were tested on Nitrous oxide (NO) gas as analyte, using a kenosistec gas sensing station. Repeatability and sensitivity of NiO gas sensor was investigated. Short response of 1.5 minutes and recovery times of 1.5 -5.1 minutes were observed on nano-structures compared to thin films. A one directional abnormal switching transition from p- to n-type conductivity response, at room temperature induced by change in nitric oxide gas concentration, was observed for non crystalline and amorphous phases of NiO/Ni(OH)2 nanostructures. NiO films (seed layers) deposited on a corning glass by DC magnetron sputtering at different substrate temperatures (25, 100, 200, 350, 450 °C). All the fabricated films and nanostructures were non-crystalline and contain amorphous phases. These NiO seed layers showed a p-type conductivity response iii expose to nitrogen monoxide gas with high response of 12 at 5 ppm (NO) for 350 °C substrate deposition temperature. The seed layers were also tested to other interference gases, such as ammonia and hydrogen, presenting meaningful responses at room operating temperature. Subsequent to the NiO films deposition, the seed layers were dipped in a hydrothermal bath solution to grow NiO/Ni(OH)2 sub-layers. The films corresponding to room deposition temperature and also 100 °C seed layer and hydrothermally grown NiO/Ni(OH)2 nanostructures, respectively, showed an n-type conductivity behaviour on the nitrogen monoxide gas of different concentration. All the sensing measurements were performed at room temperature in the presence of relative humidity of 10%. However, the 200 and 350 °C deposited seed layers of NiO/Ni(OH)2 nanostructures showed a p-type conductivity at lower concentrations (< 80 ppm) and switches to n-type behaviour at higher concentrations (≥ 80 ppm). The p-n transition is profound at 350 °C-NiO/Ni(OH)2 nanostructuresen_US
dc.identifier.urihttps://hdl.handle.net/10530/2310
dc.language.isoenen_US
dc.publisherUniversity of Zululanden_US
dc.subjectSynthesis and characterizationen_US
dc.subjectnio thin filmsen_US
dc.subjectnanostructuresen_US
dc.titleSynthesis and characterization of nio thin films and nanostructures for gas sensing applicationsen_US
dc.typeThesisen_US
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