Doctor of Philosophy (PhD), Wright State University, 2019, Electrical Engineering

Toxic chemicals have been used as chemical warfare agents since ancient times, but World War 1 saw the beginning of modern chemical proliferation. There are many methods of detecting these agents, but the combination of high sensitivity, specificity, fast response, and small form factor is difficult to achieve. More recently, graphene has been identified as a possible sensing material for ammonia and other substances. This research documents a novel method of using graphene as a chemical sensor, utilizing a radio-frequency approach to sensing. This approach utilizes all available information from the material, such as permittivity and conductivity, instead of simply examining impedance. The development of the sensor is described in depth, as well as the theoretical models used to describe its function. Finally, the overall sensitivity to ammonia, DMMP, Sarin, and VX are examined experimentally.

Committee: Yan Zhuang Ph.D. (Advisor); Fred Garber Ph.D. (Committee Member); Hong Huang Ph.D. (Committee Member); Saiyu Ren Ph.D. (Committee Member); Shin Mou Ph.D. (Committee Member) Subjects: Electrical Engineering

Doctor of Philosophy, The Ohio State University, 2012, Materials Science and Engineering

A new potentiometric CO2 gas sensor using lithium-lanthanum-titanate (Li0.35La0.55TiO3) electrolyte, Li2CO3 sensing electrode, and Li2TiO3+TiO2 reference electrode was investigated. The microstructure and electrical properties of the optimized solid electrolyte were examined and the measured conductivity values were found consistent with those reported in literature. The sensor was tested under dry condition in 21% O2/N2 at temperatures ranging from 250 to 550°C. As the temperature increased, the percentage of Nernstian behavior improved from 50% at 250°C to 95% at 450°C, but the performance degraded above 450°C. The proposed hypothesis for the degradation is as follows. Depending on CO2 partial pressure, Li2CO3 can decompose and react with Li0.35La0.55TiO3 around 475-500°C resulting in insertion of Li+ into Li0.35La0.55TiO3 that causes structural distortion. When the reaction between Li2CO3 and Li0.35La0.55TiO3 occurs at elevated temperatures such as at 700°C, the distorted structure transforms to disordered LaLi1/3Ti2/3O3 and the sensor performance degrades irreversibly. Thermodynamic calculations combined with solid-state reaction under controlled atmosphere followed by X-ray diffraction (XRD) are used to confirm the hypothesis. Finally, for device fabrication, it is demonstrated that introduction of high concentration of CO2 (~99.99%) can avoid the reaction between Li2CO3 and Li0.35La0.55TiO3 at high temperatures, which also facilitates good bonding between the electrode and the electrolyte. As for long-term device performance, it is shown that the sensor can measure changes in CO2 concentrations reproducibly as long as it is operated in conditions where there is a background of CO2, such as in ambient atmosphere or combustion systems.

Committee: Sheikh Akbar Prof/PhD (Advisor); Prabir Dutta Prof/PhD (Advisor); Gerald Frankel Prof/PhD (Committee Member); Patricia Morris Prof/PhD (Committee Member) Subjects: Materials Science

Doctor of Philosophy (Ph.D.), University of Dayton, 2023, Electrical Engineering

Doping of metal oxide semiconductors with other metal oxides or metal ions is an effective way to improve the sensing performance of gas sensors. In this dissertation, In-doped SnO2 thin film is used in different gas sensing platforms, such as surface acoustic wave (SAW) transducers and impedance spectroscopy, for the detection of volatile organic vapors at room temperature. The properties of the piezoelectric materials play a critical role in determining the sensing response of the SAW based gas sensors. Recently, various ferroelectric materials have been used as piezoelectric materials in the manufacturing of SAW based gas sensors. Among them, Ba0.6Sr0.4TiO3 (BST) has emerged as a potential candidate due to its high acoustic velocity and electromechanical coupling coefficient. In the development of gas sensors, noble metals are extensively used as electrode or transducer materials. However, noble metals are expensive and scarce. On the basis of their favorable electrical conductivity, 2D metallic transition-metal dichalcogenides (VTe2, NbTe2, and TaTe2) are emerging as promising candidates for use in 2D electronic devices. In this dissertation, the design, fabrication, and validation of BST-based SAW and NbTe2- based impedance spectroscopy sensor platforms with the In-doped SnO2 sensing film were demonstrated. Different deposition and photolithography techniques were applied to fabricate the sensors. The morphology, structural, elemental compositions, and electrical properties of the as-deposited samples were characterized by HRSEM, XRD, EDS, and the four-point probe sheet resistance method. The samples exhibited excellent film adhesion. Furthermore, the sensing performances of the SAW and impedance spectroscopy-based gas sensors towards ethanol and humidity were evaluated at room temperature. The SAW sensors exhibited a significant negative frequency shift, which can be attributed to the mass and electric loading effects o (open full item for complete abstract)

Committee: Guru Subramanyam (Advisor) Subjects: Electrical Engineering; Materials Science; Nanotechnology

PhD, University of Cincinnati, 2022, Arts and Sciences: Chemistry

Carbon nanotubes (CNTs) have exceptional electrical and mechanical properties that make them ideal materials for electrochemical sensors, including fast electron transfer rate, large aspect ratio, electrical conductance, and corrosion resistance. The individual properties can be taken advantage of by using bulk CNT devices. In this research, I have designed three different bulk assemblies of CNTs for their use as sensors for determining lead in drinking water and ammonia gas in the air. An inkjet printing recipe was formulated to print a multi-walled carbon nanotube (MWCNT) electrode optimized for detecting Pb2+ using the square wave anodic stripping voltammetry technique. The printed MWCNT electrode demonstrated a limit of detection of 1.0 ppb Pb2+ in a drinking water sample without the need for sample preparation. A gold modified CNT fiber cross-section electrode was designed for the sensitive detection of trace Pb2+ and to explore the impact water quality parameters have on the square wave stripping voltammetry technique. Six standard water parameters: pH, conductivity, free chlorine, alkalinity, temperature, and copper, both in simulated and local drinking water samples. A MWCNT film electrode was constructed using a highly ordered CNT forest array. The MWCNT film was functionalized using a facile in-situ polymerization of polyaniline (PANI) and optimized as a chemiresistive NH3 sensor. The polymerization at the CNT surface formed a porous nanostructure of PANI, a conducting polymer whose inherent resistance is sensitive to NH3. The PANI-CNT nanocomposite demonstrated detections down to ppb NH3 levels with fast response and recovery times.

Committee: Noe Alvarez Ph.D. (Committee Member); Ryan White Ph.D. (Committee Member); Ashley Ross Ph.D. (Committee Member) Subjects: Analytical Chemistry

Master of Science, University of Toledo, 0, Mechanical Engineering

The development of effective gas sensors for the detection of hazardous gases is important because of elevated concentrations of hazardous gases in the ambient. Gas sensors can be fabricated using different electronic materials such as metal oxides, carbon nanotubes, organic compounds, and ceramic compounds. Among them, metal oxides are considered as the potential materials for gas sensor application because of their high stability, high sensitivity, and ability to detect a wide range of target gases. There are some limitations associated with metal-oxide gas sensors such as low response, low conductivity, high operating temperature, and slow recovery speed. However, these limitations can be eliminated by the modification of metal oxides with impurity doping, mixing with other metal oxides, surface modification with catalytic metals. In this study, possible improvement of gas sensors by doping of impurities and addition of graphene to enhance carrier transport phenomena was investigated. Graphene was mixed with nickel oxide to produce composite films that can be used in gas sensor filament. The sensing characteristics of graphene added nickel oxide were studied as a function of graphene concentration. The samples were tested for NH3, CH4, and H2 at different operating temperatures. The response time, recovery time, cross-sensitivity, selectivity and repeatability of the test specimens were studied in details. It was found that the response, response time, recovery time, and conductivity of the films were improved after mixing of nickel oxide with graphene. The electrical properties, optical properties, and the crystal structures of the samples were studied with UV spectrophotometry and X-ray diffraction measurements. Also, zinc oxide was doped with aluminum and graphene oxide and deposited using the sol-gel method. The samples were tested for some gases and humidity. The ZnO films doped with graphene oxide and aluminum showe (open full item for complete abstract)

Committee: Ahalapitiya Jayatissa (Committee Chair); Matthew Franchetti (Committee Member); Sanjay V. Khare (Committee Member) Subjects: Materials Science; Mechanical Engineering; Nanoscience; Nanotechnology

Master of Science, Miami University, 2017, Physics

The electric conductance of ZnO:Sb micro/nanowires has a rich behavior that can be utilized in sensing applications. This electric conductance readily depends on the ambient temperature, light and the abundance of oxygen around the wire. Through a systematic study we show the effects of light illumination, temperature variation, and oxygen gas flow on the persistent photoconductance of ZnO:Sb micro and nanowires for the development of reliable and stable oxygen gas sensors. The three parameters impact the resistance through the same mechanism of oxygen adsorption and desorption from the surface of ZnO:Sb wire, thus it is important to choose the right temperature and light illumination for efficient and reliable gas sensing.

Committee: Khalid Eid (Advisor); Herbert Jaeger (Committee Member); Lei Kerr (Committee Member) Subjects: Physics

Master of Science in Engineering, University of Akron, 2017, Mechanical Engineering

One of the applications of polymer electrolyte fuel cells is using them as gas concentration measurement sensors. Since various gases can react with air in fuel cells, the concentration of the gas can be determined using the generated current density and calibration curve of the fuel cell sensor. Currently, the most challenging issues regarding fuel cell sensors are their durability and production cost due to their high amount of platinum (Pt) catalyst used to fabricate the sensor. In this study, fuel cell sensors with polymer electrolyte membrane for ethanol gas concentration measurement in human exhaled breath were studied for the purpose of determination of the best electrode Pt catalyst loadings and polymer electrolyte membrane in terms of reducing the sensor production cost and improving the sensor linear response and durability. The results of experiments using a fully automated test system with LabVIEW software package, consisting of a breath simulator, a potentiostat, a highly accurate multimeter, several fastresponse solenoid valves, and a 3D printed sensor housing, have been obtained and presented. The results confirm that the sensor Pt catalyst loading can be reduced by approximately 130 times compared to the catalyst loading in commercial sensors without notably changes on the sensor performance. In addition, the fabrication of sensors with very low Pt loading on the cathode side is possible and can be economically favorable for manufacturing ethanol gas sensors. It also has been shown that the peak current density measurement method, which expedites the sensor recovering time, can be used for low catalyst loading sensors due to the observation of very good linearity behavior of the sensor with changing the ethanol gas concentration. Finally and after the validation of the sensor performance, a Nafion study and a durability study has been done. It was concluded that Nafion 115, 117, 438 and 1110 have the highest current density and (open full item for complete abstract)

Committee: Siamak Farhad (Advisor); Gaurav Mittal (Committee Member); Jae-Won Choi (Committee Member) Subjects: Chemical Engineering; Mechanical Engineering

Doctor of Philosophy (PhD), Wright State University, 2014, Engineering PhD

Novel silicene-based nanomaterials are designed and characterized by first principle computer simulations to assess the effects of adsorptions and defects on stability, electronic, and thermal properties. To explore quantum thermal transport in nanostructures a general purpose code based on Green's function formalism is developed. Specifically, we explore the energetics, temperature dependent dynamics, phonon frequencies, and electronic structure associated with lithium chemisorption on silicene. Our results predict the stability of completely lithiated silicene sheets (silicel) in which lithium atoms adsorb on the atom-down sites on both sides of the silicene sheet. Upon complete lithiation, the band structure of silicene is transformed from a zero-gap semiconductor to a 0.368 eV bandgap semiconductor. This new, uniquely stable, two-atom-thick, semiconductor material could be of interest for nanoscale electronic devices. We further explore the electronic tunability of silicene through molecular adsorption of CO, CO2, O2, N2, and H2O on nanoribbons for potential gas sensor applications. We find that quantum conduction is detectibly modified by weak chemisorption of a single CO molecule on a pristine silicene nanoribbon. Moderate binding energies provide an optimal mix of high detectability and recoverability. With Ag contacts attached to a ~ 1 nm silicene nanoribbon, the interface states mask the conductance modulations caused by CO adsorption, emphasizing length effects for sensor applications. The effects of atmospheric gases: nitrogen, oxygen, carbon dioxide, and water, as well as CO adsorption density and edge-dangling bond defects, on sensor functionality are also investigated. Our results reveal pristine silicene nanoribbons as a promising new sensing material with single molecule resolution. Next, the thermal conductance of silicene nanoribbons with and without defects is explored by Non-Equilibrium Green's function method as implemented in our Th (open full item for complete abstract)

Committee: Amir Farajian Ph.D. (Advisor); Khalid Lafdi Ph.D. (Committee Member); Sharmila Mukhopadhyay Ph.D. (Committee Member); Ajit Roy Ph.D. (Committee Member); H. Daniel Young Ph.D. (Committee Member) Subjects: Materials Science; Nanoscience; Nanotechnology

Doctor of Philosophy, University of Toledo, 2014, College of Engineering

The increasing concerns of industrial safety, chemical control and environmental pollution are spurring demand for high performance gas sensors. Growing use of gas sensors is making gas sensors on demand. After decades of research and development activities, semiconductor based gas sensors are now used in a variety of applications. However, challenges still remain in the area of sensitivity, selectivity, response and recovery speeds and power consumption. Therefore, improvement of metal oxide gas sensors by the incorporation of different technology is important. In this research, modification of metal oxide semiconductor based gas sensor by impurity doping, laser irradiation, and plasma treatment was investigated. Zinc oxide (ZnO) is an n-type semiconductor with a wide direct band gap (~3.3 eV) and large binding energy (~60 meV). Due to its superior electrical properties and chemical stability, ZnO has been considered one of the most promising materials for gas sensor applications. ZnO thin films have been fabricated by different techniques, such as rf magnetron sputtering, pulsed laser deposition, molecular beam epitaxy, and sol-gel. Sol-gel is a powerful alternative for vacuum deposition. iii The purpose of this research was to enhance properties and gas sensor performance of nanocrystalline so-gel derived ZnO thin films via surface modification techniques. The effects of process conditions, impurity doping, laser irradiation, laser doping and plasma treatment on properties and gas sensor performance were investigated. The gas sensor performance of ZnO thin films was investigated at different operating temperatures for various reducing and oxidizing gases such as H2, NH3, CH4 and NOx. Al-doped ZnO thin films were prepared using the sol-gel process by changing the Al concentration from 0 to 5.0 at% using two different Zn precursors. It was found that 3.0 at% Al-doped ZnO films had optimum properties such as high electrical conductivity, crystallinity, high sens (open full item for complete abstract)

Committee: Ahalapitiya Jayatissa (Committee Chair); Sanjay Khare (Committee Member); Lesley Berhan (Committee Member); Mehdi Pourazady (Committee Member); Sorin Cioc (Committee Member); Ambalangodage Jayasuriya (Committee Member) Subjects: Materials Science; Mechanical Engineering

Doctor of Philosophy, The Ohio State University, 2010, Chemical and Biomolecular Engineering

Fluidized beds provide good mass and heat transfer characteristics, temperature homogeneity and high flowability of particles. Gas-solid fluidized beds have been employed extensively in chemical, petrochemical, metallurgical, food, and pharmaceutical industries. A comprehensive understanding of the complex hydrodynamics and transport phenomena in gas-solid fluidized beds are required for successful application of these systems in industry. Moreover, much of the fundamental research reported in the literature on gas-solid fluidization properties have been performed with large gas-solid fluidized beds. Little is known about gas-solid fluidization in the mini- and micro-scale channel sizes ranging from 10-3 m to 10-2 m and 10-4 m to 10-5 m, respectively. A comprehensive study on the hydrodynamics of gas-solid fluidization and the significant wall effect in the mini- and micro-channels is needed for micro-scale reactor design. In this study, the dynamic flow behaviors in gas-solid fluidized beds are investigated by using Electrical Capacitance Volume Tomography (ECVT). Several advanced cylindrical and bend ECVT sensors are developed for the measurements. The instantaneous properties of the shape of the jets, and volumetric solids holdup of three-dimensional horizontal gas and gas/solid mixture jetting in a 0.3 m ID bubbling gas-solid fluidized bed are qualified and quantified using ECVT. The prediction from a mechanistic model established in this study and the ECVT experiments both show that the maximum penetration length and width of the horizontal gas jet increase with the superficial gas velocity in the bed. The average solids concentrations in a 0.1 m ID and 0.3 m ID beds are consistent with each other, but are higher than that in a 0.05 m ID bed at a given superficial gas velocity. The bubble size determined from ECVT with a threshold value of 0.3 for the solids concentration is consistent with those from the literature. In a 0.05 m ID gas-solid circulating fluidiz (open full item for complete abstract)

Committee: Liang-Shih Fan PhD (Advisor); L. James Lee PhD (Committee Member); Isamu Kusaka PhD (Committee Member) Subjects: Chemical Engineering

Doctor of Philosophy, The Ohio State University, 2009, Chemistry

The growth of zeolite L membranes with controlled thicknesses in the sub-micron to micron region is examined. It was demonstrated that by controlling the concentration of the zeolite solid load and suspension viscosity, dip-coating provided a method to prepare zeolite seed layers of controlled thicknesses. Disk-shaped zeolite L crystals, with size distribution of 0.5-2 microns in diameter, were used as seed crystals for the growth of 2-7 micron thick membranes. For the synthesis of sub-micron sized membranes, seed crystals from 20-60 nanometers were used. The optimum secondary growth conditions was found to occur at 60 hours of growth time (40 hours for sub-micron membranes) using a temperature of 110°C with a solution composition of 10K2O:1Al2O3:20SiO2:2000H2O. Membranes were characterized by electron microscopy and single gas permeation studies, providing confirmation of membrane densification. Composite, defect-free membranes consisting of zeolite Y layers on the surface of microporous α-Al2O3 support disks were prepared using externally synthesized nanocrystalline and sub-micron crystals. Polycrystalline layers were formed by two different hydrothermal secondary growth procedures. Nanocrystalline zeolite Y seeded membranes were utilized as chemical sensors for the detection of chemical warfare agents. Sensor traces were established to show that despite the good membrane sensitivity to DMMP, sensor recovery times were too long for practical applications. Due to the ability of small molecules to pass one another inside the micropores of zeolites, two different zeolite Y membrane types were prepared from sub-micron crystallites to investigate their gas transport and separation properties. Single gas permeances for helium were determined in the temperature range of 30-130°C for both membrane types. The separation factors of equimolar mixtures of CO2 and N2 were measured at the same temperatures and at feed pressures from 1.4-4 bar. Both membrane types showed high s (open full item for complete abstract)

Committee: Prabir Dutta PhD (Advisor); Susan Olesik PhD (Committee Member); Patrick Woodward PhD (Committee Member); Rajendra Singh PhD (Committee Member) Subjects: Chemistry; Materials Science

Doctor of Philosophy, The Ohio State University, 2004, Materials Science and Engineering

An electrochemical CO2 gas sensor with lithium ion conductor was developed and characterized in order to examine the potential for real-life applications and understand its sensing mechanism. Li2CO3 and Li2TiO3+TiO2 mixture were used as a sensing and a reference auxiliary phase, respectively. This electrochemical cell with a solid state Li3PO4 electrolyte has shown good selectivity, sensitivity and linear response in laboratory and automobile exhaust tests. However, the sensor response to CO2 gas showed a systematic deviation from the Nernst equation. Measured EMF did not agree with that calculated from the Nernst equation, even though it followed logarithmic behavior. Moreover, high sensitivity was observed for high CO2 concentrations (5~50%), compared to that for concentrations (500~5000 ppm). Two possible reasons for this deviation are: (1) reversibility of electrode reaction and (2) mixed ionic and electronic conduction of the electrolyte. Unless electrode reaction is fast enough, electrode polarization can easily induce overpotential. Pure ionic conduction of electrolyte is also necessary to avoid EMF loss during open circuit potential measurement. EIS (Electrochemical Impedance Spectroscopy) was used to study electrode kinetics. We found that Li2TiO3+TiO2 mixture reference electrode reaction is sluggish showing large electrode impedance. This impedance, however, was not affected by gas concentration change. On the other hand, that at the Li2CO3 sensing electrode is relatively small and it increased with decreased CO2 and O2 concentration. It was also observed that these electrode impedances induced the overpotential when the current flowed through the sensor. This electrode overpotential problem was minimized by mixing gold powder or porous sputtered gold electrode increasing effective reaction sites of the electrode. New electrode design improved the sensor EMF closer to the Nernstian values, however, the discrepancy still remained. Moreover, at higher sensor (open full item for complete abstract)

Committee: Sheikh Akbar (Advisor) Subjects: Engineering, Materials Science

Doctor of Philosophy, The Ohio State University, 2003, Chemistry

TiO2-based sensors were developed and characterized for improvement of selectivity and sensitivity towards CO gas at high temperatures. Selectivity was improved by combining several sensors into an array, while sensitivity improvement was studied by examination of the effects of various metal and metal oxide additives and reactive sputtering film preparation. TiO2-based sensors containing La2O3 and La2O3/CuO were combined into an array for testing of CO and O2 gas mixtures. Nonlinear regression analysis was developed to determine the concentrations of gases in the mixture. The regression technique can be used to determine the prediction ability of gas sensor combinations for given gas concentration ranges using a defined orthogonality index, as well as to determine the amount of each gas in the mixture based on the responses of a set of sensors. The prediction ability for a La2O3-containing sensor combined with La2O3/CuO-containing sensors with varying levels of CuO are compared for a range of CO and O2 concentrations. Concentrations of CO and O2 in gas mixtures are predicted using the La2O3- and La2O3/CuO-containing sensors and the regression analysis. Addition of various metals and metal oxides, including Au, CuO and La2O3 to TiO2-based gas sensors has been examined to determine the effect of additives on the gas-surface reactivity and electrical response of the sensors. Electrical measurements show that sensor sensitivity is decreased upon addition of La2O3 with only a slight increase in sensitivity when CuO is added to La2O3-containing sensors. Au, however, was found to increase the sensitivity of the TiO2-based sensors with and without La2O3. Gas chromatography was used to determine the catalytic conversion of CO for the various sensor materials at different temperatures for comparison with electrical measurements. General guidelines for additive selection have been proposed based on the results. Reactively sputtered thin film TiO2 gas sensors have been fabrica (open full item for complete abstract)

Committee: Prabir Dutta (Advisor) Subjects: Chemistry, Analytical

Doctor of Philosophy, Case Western Reserve University, 2012, Physics

Semiconductor nanowires are believed to be one of most promising building blocks in nanotechnology. In this dissertation, we report the controlled synthesis and quantum transport in InAs nanowires and topological insulator Bi2Se3 nanoribbons, two small band gap semiconductors with important applications in high speed transistor, spintronics, thermoelectric, etc. First, InAs nanowires and Bi2Se3 nanoribbons were synthesized based on the Au nanoparticle catalyzed vapor-liquid-solid mechanism in a chemical vapor deposition system. We first found that small vacuum leakage in the system incorporated oxygen in the InAs nanowires. Such nanowires exhibit low electron mobility (~100 cm2/Vs). Upon improving the system vacuum sealing, we showed that pure InAs nanowires with correct stoichiometry and superior mobility (~1000 cm2/Vs) can be consistently grown. Particularly, we studied the effect of Au nanoparticles' shape on InAs nanowire growth and found that shaped Au nanoparticles can double the average growth rate compared with spherical ones. We attributed this enhanced growth rate to the better wetting ability of non-melted flat facets in shaped Au nanoparticles. Secondly, due to the small diameter (<100nm) of nanowires, low temperature electronic transport of the nanowires can be low dimensional and quantum mechanical in nature. For low mobility InAs nanowires, one-dimensional weak localization was observed. The anisotropic suppression of weak localization in these nanowires was studied and attributed to the radial size confinement of time reversed electron diffusion paths. For pure InAs nanowires with high mobility, weak anti-localization was observed due to strong intrinsic spin orbit interaction. We further demonstrated the application of a surrounding electrolyte gate scheme to tune the Rashba spin orbit interaction by six fold within 1 V of gate voltage. Thirdly, we performed magneto-transport study of nanoribbons of topological insulator materials (Bi2Se3, Bi2 (open full item for complete abstract)

Committee: Xuan Gao PhD (Advisor); Kathleen Kash PhD (Committee Member); Jie Shan PhD (Committee Member); Mohan Sankaran PhD (Committee Member) Subjects: Condensed Matter Physics; Low Temperature Physics; Nanoscience; Nanotechnology; Quantum Physics

Doctor of Philosophy in Engineering, University of Toledo, 2013, Mechanical Engineering

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 e (open full item for complete abstract)

Committee: Ahalapitiya Jayatissa (Committee Chair); Lesley Berhar (Committee Member); Sarit Bhaduri (Committee Member); Sanjay Khare (Committee Member); Mehdi Pourazady (Committee Member) Subjects: Mechanical Engineering