EAGER: Low-cost Sensors for real-time monitoring of environment using Mobile Devices

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Measuring individual exposure in real-time can revolutionize air quality monitoring in communities everywhere. Such information would allow citizens to take preventive measures to reduce their exposures to air toxins, which would tremendously impact their health and quality of life. Mobile devices such as smart-phones and tablets represent a powerful infrastructure which could be leveraged to develop personal air monitors. However, traditional sensor technologies (such as electrochemical and photo-ionization detectors), commonly used for industrial safety monitoring, are big, power-hungry, and has limited sensitivity and life-time. The goal of this EAGER is to explore a highly-selective sensor architecture, utilizing nanoengineered gallium nitride (GaN) photoconductors functionalized with multicomponent nanoclusters of metal-oxides and metals. Innovation in photo-enabled sensing makes it possible to operate these sensors at room-temperature and resulting in significant reduction in operating power. The strength of this approach is that it uses all standard microfabrication techniques, for developing economical, multi-analyte, single-chip sensor solution. Due to the use of inert wide-bandgap semiconductor, metal-oxides, and noble metals, the environmental impact of these sensors during their life cycles is minimal. The proposed exploratory work will be done in collaboration with NIST and N5 Sensors Inc. Future prospects of such low-power, small form-factor sensors include embedded-chip or plug-in module with multi-analyte sensor arrays for the smart phones for citizens and soldiers for acquiring real-time environmental information. The research provides an excellent opportunity for a graduate student from an underrepresented group, undergraduate students, and students from Thomas Jefferson High School of Science and Technology to work on the project using state-of-art research facilities at NIST and N5 sensors Inc. Integration of the research with a graduate level course is also proposed.The main goal of this project is to develop a technology for mobile devices to rapidly trace and monitor air toxins in indoor and outdoor environments. To achieve different analyte selectivity, the GaN sub-micrometer photoconductors will be coated with different grain size and crystallographic phases of metals and metal oxides. Heated powder mixtures of TiO2 and WO3 will be tried to achieve high sensitivity to N2O. The basic scientific work includes simulations to gain fundamental understanding of the surface science associated with metal-oxide active site surface adsorption. First-principles Density Functional Theory (DFT) calculations using the Vienna Ab Initio Simulation Package (VASP) will be used to study NO2 and SO2 interactions with metal and metal-oxide surfaces of various morphologies. The SO2 and NO2 adsorption on ideal extended surfaces and defect sites of model metal and metal-oxides (WO3, Pt (111), TiO2, Fe (111)) will be studied. Based on DFT calculations metal-oxide nanoclusters for coating the GaN photoconductor backbone will be selected. The GaN photoconductor fabrication process and the nanoclusters deposition process will be optimized to obtain desired phase, morphology, surface defect structure for achieving the desired sensitivity and selectivity. Sensors will be thoroughly characterized for their sensing performance and reliability. Devices will be field tested for personal exposure monitoring.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.