Date on Master's Thesis/Doctoral Dissertation

12-2017

Document Type

Doctoral Dissertation

Degree Name

Ph. D.

Department

Physics and Astronomy

Degree Program

Physics, PhD

Committee Chair

Jayanthi, Chakram

Committee Member

Sumanasekera, Gamini

Committee Member

Dobrokhotov, Valdimir

Committee Member

Mendes, Sergio

Author's Keywords

micro hot plates; metal oxide gas sensor array; nanocomposite thin films; bimetal nanoparticles; multidimensional gas chromatography; portable gas mixture analysis

Abstract

Gas analysis is an important part of our world and gas sensing technology is becoming more essential for various aspects of our life. A novel approach for gas mixture analysis by using portable gas chromatography in combination with an array of highly integrated and selective metal oxide (MOX) sensors has been studied. We developed a system with small size (7 x 13 x 16 inches), low power consumption (~10 W) and absence of special carrier gases designed for portable field analysis (assuming apriori calibration). Low ppb and even sub-ppb level of detection for some VOCs was achieved during the analysis of 50 ml of gas samples. A detailed description of our innovative design of multi-sensory platforms based on MOX sensors for multidimensional portable gas chromatography is provided in detail in this work. As a part of this effort, we successfully synthesized nanocomposite gas sensors based on SnO2 for selective detection of hydrogen sulfide, mercaptans, alcohols, ketones and heavy hydrocarbons. The morphology of the prepared sensors was closely studied by scanning electron microscopy (SEM), atomic force microscopy (AFM), transition electron microscopy (TEM) and X-Ray diffraction (XRD). Optical and electrical properties of polycrystalline SnO2 were investigated by using UV-Vis spectroscopy, transmission line measurement (TLM) and four probe resistance measurement techniques. Furthermore, more advanced gas sensing performance for detection of benzene, toluene, ethylbenzene, and O-xylene (BTEX) of polycrystalline SnO2 film (30 nm) coated with bimetal Au:Pd (9:1 molar ratio) nanoclusters was measured. Finally, besides the experimental result, the theoretical validation of the detector’s performance was provided based on high catalytic activity of nanocomposite materials and its superior electronic structure for gas detection compared to the polycrystalline SnO2. The theoretical background of gas chemisorption process at the surface of polycrystalline SnO2 was reviewed in this work. Furthermore, one dimensional Poisson equation relates surface energy states ( and ) and the bulk electronic structure ( and ) of polycrystalline SnO2. The main theory of electronic processes on the surface of semiconductors during the gas chemisorption was further applied in a case of nanocomposite materials.

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