Synthesis, Fabrication and Surface Modification of Nanocrystalline Nickel Oxide for Electronic Gas Sensors

Recently, metal oxide gas sensors have attracted much attention in connection with monitoring of combustible and toxic gases because of their higher sensitivity, fast response and recovery times, low power consumption, and low fabrication cost. Nickel oxide (NiO) is a wide band gap and p-type semiconductor with stable chemical and physical properties. NiO has been recognized as one of the most promising material for optical, electrical and gas sensor application owing to its electronic and catalytic properties. NiO is synthesized using different techniques, such as pulsed laser deposition, RF sputtering, electrochemical deposition and sol-gel. The focus of this research was to synthesize and characterize the gas sensing behavior of nickel oxide metal oxide gas sensors. Thin films of nickel oxide synthesized by a sol-gel method have fine nanostructured grains with a high surface to volume ratio, which is beneficial for gas sensor applications. The effect of thickness, fabricating technique, operating temperature, post laser irradiation and metallization on the gas sensing behavior of nickel oxide have been studied. The microstructure, optical and electrical properties of coated film were studied by XRD, SEM, TEM, EDAX, XPS, UV-Vis spectrometer. The gas sensing properties of NiO based sensors were studied for different explosive and hazardous gases as a function of gas concentration and operating temperature.The dependence of fabrication method, film thickness and operating temperature on the hydrogen gas sensing behavior of NiO thin films was investigated. It was observed that the samples with multi-step annealing possessed smaller grain size, higher porosity and higher gas sensing performance. The sample with lower thickness showed better gas sensing performance in all operating temperatures. Moreover, the operating temperature was an important parameter for nickel oxide thin film, and the maximum gas sensor response was recorded at 175oC for hydrogen gas. The effect of post laser irradiation on the gas sensing property of NiO was investigated using Nd:YVO4 laser with a wavelength of 532 nm in different power levels. After laser irradiation, the microstructure, crystallinity and conductivity of the thin films were changed. Results indicated that the irradiated sample with specific power showed better gas sensing performance for hydrogen. Also, the gas sensor response decreased using laser irradiation on the sample. As a result, laser irradiation is an additional tool for tuning the gas sensing behavior of nickel oxide gas sensor. Later, the nickel oxide film was tested for other reducing gases, such as CH4, NH3, and in a mixed gas environment at different operating temperatures. These measurements were conducted to study the selectivity of nickel oxide gas sensor. It was found that the NiO thin film showed a relatively high response to a low concentration of ammonia gas (25 ppm) at a relatively low operating temperature. Instead, the sample showed a relatively low response to methane gas compared to hydrogen and ammonia in the same concentration level. Besides, the gas response of the device at different operating temperature was studied for reducing gases. The film showed a maximum sensitivity for methane and hydrogen gases at 175oC, and the highest response was recorded at 150oC for ammonia gas. These findings are valuable to design selective gas sensors. Finally, Pt decorated sample was tested for various concentrations of hydrogen gas at different operating temperature. The gas sensing property of the film was improved significantly due to the catalyst effect of Pt particles on the surface of metal oxide. Pt decorated sample increased the hydrogen sensing property of nickel oxide by decreasing the energy needed for splitting H2 or O2 molecules on the surface of metal oxide.This study shows several important parameters for nickel oxide gas sensors and it is expected that these techniques can be used to improve the gas sensing performance of different metal oxide gas sensor devices in the future. Collected data at various operating temperatures and gas mixtures can be used to design more selective gas sensors. More detailed research is necessary to establish a general rule for other metal oxide thin films.

Name thesis:degree_name

Doctor of Philosophy in Engineering

Level thesis:degree_level

doctoral

Discipline thesis:degree_discipline

Mechanical Engineering

Grantor dc:publisher

University of Toledo

Year dc:date

2013

Author dc:creator

• Soleimanpour, Amir Masoud

Contributors dc:contributor

• Jayatissa, Ahalapitiya

• Mechanical Engineering
• nickel oxide
• gas sensor, hydrogen sensor, ammonia sensor, methane sensor, laser irradiation, cross sensitivity, sol-gel

Statement dc:rights

• unrestricted
• This thesis or dissertation is protected by copyright: all rights reserved. It may not be copied or redistributed beyond the terms of applicable copyright laws.

Language dc:language

English

Repository record dc:identifier

http://rave.ohiolink.edu/etdc/view?acc_num=toledo1365071722

OAI identifier oai:identifier

oai:etd.ohiolink.edu:toledo1365071722