{"id":{"repo_id":"houston","oai_identifier":"oai:uh-ir.tdl.org:10657/20837"},"canonical_url":"https://search.dev.ndltd.org/etd/houston/oai:uh-ir.tdl.org:10657/20837","repository":{"repo_id":"houston","name":"University of Houston","base_url":"https://uh-ir.tdl.org/server/oai/request"},"display":{"title":"Development of ZnO Nanotube Arrays for Chemical Sensing","abstract":"The world today faces three interconnected issues: global warming, air pollution, and the rise in cancer rates. The common cause is the excessive use of fossil fuels. It has been widely recognized that net-zero emissions should be achieved before the year 2050. Hydrogen produced using renewable sources is a clean energy vector that could help the world achieve this goal. Nevertheless, hydrogen leakage can cause more global warming as it prolongs methane lifetimes in the atmosphere. Therefore, there is a need to promptly detect hydrogen leaks as its production and utilization increase with the paradigm shift in the energy system. At the same time, the increase in the overall cancer rates, which can also be correlated with environmental pollution, remains a critical challenge in global healthcare. Detection of volatile organic compounds (VOC) in exhaled gas that are cancer biomarkers is emerging as a viable approach for early-stage cancer detection. Gas sensing technologies, particularly those based on low-cost semiconductor metal oxides (SMOX), offer feasible solutions to both these problems. Nevertheless, the application of SMOX sensors in these areas faces challenges due to inadequate sensitivity to target species and cross-sensitivity to non-target species. In this dissertation work, we addressed these critical problems through the development of a new material, anodic ZnO nanotube array, as the sensing platform and the application of artificial intelligence to a sensor system developed using this material. The nanotube array geometry showed specific light scattering properties, as revealed by the finite difference time domain simulations, that are useful for the application of this semiconductor in solar devices. The density functional theory calculations showed distinct quantum conductance of the material. By using morphology-controlled synthesis and defect engineering and by applying machine learning algorithms to discriminate the response patterns of an array of sensors, we could achieve high selectivity, low detection limit, and low temperature of operation. This research demonstrated the potential of the material to be the platform for a single, affordable sensing technology to play dual critical roles: real-time monitoring of hydrogen in the environment and detection of breath VOCs for early-stage breast cancer detection.","abstract_html":"The world today faces three interconnected issues: global warming, air pollution, and the rise in cancer rates. The common cause is the excessive use of fossil fuels. It has been widely recognized that net-zero emissions should be achieved before the year 2050. Hydrogen produced using renewable sources is a clean energy vector that could help the world achieve this goal. Nevertheless, hydrogen leakage can cause more global warming as it prolongs methane lifetimes in the atmosphere. Therefore, there is a need to promptly detect hydrogen leaks as its production and utilization increase with the paradigm shift in the energy system. At the same time, the increase in the overall cancer rates, which can also be correlated with environmental pollution, remains a critical challenge in global healthcare. Detection of volatile organic compounds (VOC) in exhaled gas that are cancer biomarkers is emerging as a viable approach for early-stage cancer detection. Gas sensing technologies, particularly those based on low-cost semiconductor metal oxides (SMOX), offer feasible solutions to both these problems. Nevertheless, the application of SMOX sensors in these areas faces challenges due to inadequate sensitivity to target species and cross-sensitivity to non-target species. In this dissertation work, we addressed these critical problems through the development of a new material, anodic ZnO nanotube array, as the sensing platform and the application of artificial intelligence to a sensor system developed using this material. The nanotube array geometry showed specific light scattering properties, as revealed by the finite difference time domain simulations, that are useful for the application of this semiconductor in solar devices. The density functional theory calculations showed distinct quantum conductance of the material. By using morphology-controlled synthesis and defect engineering and by applying machine learning algorithms to discriminate the response patterns of an array of sensors, we could achieve high selectivity, low detection limit, and low temperature of operation. This research demonstrated the potential of the material to be the platform for a single, affordable sensing technology to play dual critical roles: real-time monitoring of hydrogen in the environment and detection of breath VOCs for early-stage breast cancer detection.","abstract_has_math":false,"creators":["Waligo, David 1994-"],"institution":"University of Houston","degree_name":"Doctor of Philosophy","degree_level":null,"degree_discipline":"Physics","degree_department":null,"school":null,"contributors":[],"advisors":["Varghese, Oomman K."],"committee_chairs":[],"committee_members":["Grabow, Lars C.","Freelon, Byron K.","Chen, Shuo","Ting, Chin S."],"year":2025,"date_issued":"2025-12","date_published":"2025-12","updated_at":"2026-07-24T02:33:01Z","subjects":["Breast cancer","Electronic nose","Sensor array"],"languages":["English"],"rights":[],"rights_urls":[],"identifier_entries":[]},"links":{"outbound_url":"https://hdl.handle.net/10657/20837","outbound_label":"Handle","outbound_source":"dc:identifier.uri"},"metadata_groups":[{"id":"people","label":"People","entries":[{"key":"dc:contributor.advisor","label":"Advisor","values":["Varghese, Oomman K."]},{"key":"dc:contributor.committeemember","label":"Committee Member","values":["Grabow, Lars C.","Freelon, Byron K.","Chen, Shuo","Ting, Chin S."]},{"key":"dc:creator","label":"Author","values":["Waligo, David 1994-"]}]},{"id":"academic_context","label":"Academic Context","entries":[{"key":"dc:date.accessioned","label":"Dc Date Accessioned","values":["2026-02-05T16:34:12Z"]},{"key":"dc:date.issued","label":"Date","values":["2025-12"]},{"key":"dc:type","label":"Dc Type","values":["Thesis"]},{"key":"thesis:degree_discipline","label":"Discipline","values":["Physics"]},{"key":"thesis:degree_name","label":"Degree Name","values":["Doctor of Philosophy"]},{"key":"thesis:institution_name","label":"Thesis Institution Name","values":["University of Houston"]}]},{"id":"subjects_keywords","label":"Subjects and Keywords","entries":[{"key":"dc:subject","label":"Dc Subject","values":["Breast cancer","Electronic nose","Sensor array"]}]},{"id":"language_rights","label":"Language and Rights","entries":[{"key":"dc:language.iso","label":"Language (ISO)","values":["English"]}]},{"id":"identifiers","label":"Identifiers","entries":[{"key":"dc:identifier.uri","label":"Identifier URI","values":["https://hdl.handle.net/10657/20837"]}]},{"id":"additional","label":"Additional Metadata","entries":[{"key":"dc:description.abstract","label":"Abstract","values":["The world today faces three interconnected issues: global warming, air pollution, and the rise in cancer rates. The common cause is the excessive use of fossil fuels. It has been widely recognized that net-zero emissions should be achieved before the year 2050. Hydrogen produced using renewable sources is a clean energy vector that could help the world achieve this goal. Nevertheless, hydrogen leakage can cause more global warming as it prolongs methane lifetimes in the atmosphere. Therefore, there is a need to promptly detect hydrogen leaks as its production and utilization increase with the paradigm shift in the energy system. At the same time, the increase in the overall cancer rates, which can also be correlated with environmental pollution, remains a critical challenge in global healthcare. Detection of volatile organic compounds (VOC) in exhaled gas that are cancer biomarkers is emerging as a viable approach for early-stage cancer detection. Gas sensing technologies, particularly those based on low-cost semiconductor metal oxides (SMOX), offer feasible solutions to both these problems. Nevertheless, the application of SMOX sensors in these areas faces challenges due to inadequate sensitivity to target species and cross-sensitivity to non-target species. In this dissertation work, we addressed these critical problems through the development of a new material, anodic ZnO nanotube array, as the sensing platform and the application of artificial intelligence to a sensor system developed using this material. The nanotube array geometry showed specific light scattering properties, as revealed by the finite difference time domain simulations, that are useful for the application of this semiconductor in solar devices. The density functional theory calculations showed distinct quantum conductance of the material. By using morphology-controlled synthesis and defect engineering and by applying machine learning algorithms to discriminate the response patterns of an array of sensors, we could achieve high selectivity, low detection limit, and low temperature of operation. This research demonstrated the potential of the material to be the platform for a single, affordable sensing technology to play dual critical roles: real-time monitoring of hydrogen in the environment and detection of breath VOCs for early-stage breast cancer detection."]},{"key":"dc:format.mimetype","label":"Dc Format Mimetype","values":["application/pdf"]},{"key":"dc:title","label":"Title","values":["Development of ZnO Nanotube Arrays for Chemical Sensing"]}]}],"canonical_facts":{"dc:contributor.advisor":["Varghese, Oomman K."],"dc:contributor.committeemember":["Grabow, Lars C.","Freelon, Byron K.","Chen, Shuo","Ting, Chin S."],"dc:creator":["Waligo, David 1994-"],"dc:date.accessioned":["2026-02-05T16:34:12Z"],"dc:date.issued":["2025-12"],"dc:description.abstract":["The world today faces three interconnected issues: global warming, air pollution, and the rise in cancer rates. The common cause is the excessive use of fossil fuels. It has been widely recognized that net-zero emissions should be achieved before the year 2050. Hydrogen produced using renewable sources is a clean energy vector that could help the world achieve this goal. Nevertheless, hydrogen leakage can cause more global warming as it prolongs methane lifetimes in the atmosphere. Therefore, there is a need to promptly detect hydrogen leaks as its production and utilization increase with the paradigm shift in the energy system. At the same time, the increase in the overall cancer rates, which can also be correlated with environmental pollution, remains a critical challenge in global healthcare. Detection of volatile organic compounds (VOC) in exhaled gas that are cancer biomarkers is emerging as a viable approach for early-stage cancer detection. Gas sensing technologies, particularly those based on low-cost semiconductor metal oxides (SMOX), offer feasible solutions to both these problems. Nevertheless, the application of SMOX sensors in these areas faces challenges due to inadequate sensitivity to target species and cross-sensitivity to non-target species. In this dissertation work, we addressed these critical problems through the development of a new material, anodic ZnO nanotube array, as the sensing platform and the application of artificial intelligence to a sensor system developed using this material. The nanotube array geometry showed specific light scattering properties, as revealed by the finite difference time domain simulations, that are useful for the application of this semiconductor in solar devices. The density functional theory calculations showed distinct quantum conductance of the material. By using morphology-controlled synthesis and defect engineering and by applying machine learning algorithms to discriminate the response patterns of an array of sensors, we could achieve high selectivity, low detection limit, and low temperature of operation. This research demonstrated the potential of the material to be the platform for a single, affordable sensing technology to play dual critical roles: real-time monitoring of hydrogen in the environment and detection of breath VOCs for early-stage breast cancer detection."],"dc:format.mimetype":["application/pdf"],"dc:identifier.uri":["https://hdl.handle.net/10657/20837"],"dc:language.iso":["English"],"dc:subject":["Breast cancer","Electronic nose","Sensor array"],"dc:title":["Development of ZnO Nanotube Arrays for Chemical Sensing"],"dc:type":["Thesis"],"thesis:degree_discipline":["Physics"],"thesis:degree_name":["Doctor of Philosophy"],"thesis:institution_name":["University of Houston"]},"updated_at":"2026-07-24T02:33:01Z"}