CAREER: Real-Time, Selective Gas Sensing in Complex Gas Compositions by Molecular Sieving via Robust Two-Dimensional Heterostructures

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This award is funded in whole or in part under the American Rescue Plan Act of 2021 (Public Law 117-2).There has been an increasing need for real-time, discriminate, sensitive, and low-cost gas sensors to promote human health and safety in a changing world. These are needed for non-invasive medical screening and diagnostics, environmental sensing, and explosives detection. However, complex gas compositions, like those found in the human breath or the environment, make conventional selective gas detection challenging. Current solid-state sensors, while low-cost and robust, suffer from poor selectivity in complex gas compositions. This NSF CAREER research program aims to investigate the gas sieving capabilities of the interlayer gap between layered two-dimensional materials for the tunable, selective, electrical detection of gas molecules. This project's educational and outreach goal is to engage underrepresented minorities in STEM programs through course-based undergraduate research experiences, internships, and mentorships with local high schools.The research objective of this CAREER proposal is to address the speed and selectivity problems in low-cost solid-state gas sensors by investigating and exploiting the unparalleled electronic and sensing properties of 2D epitaxial graphene (EG) on silicon carbide with heterostructures comprised of 2D layered transition metal oxides (TMO). TMOs innate chemical selectivity and uniquely wide interlayer spacings can be manipulated ionically to enable tunable molecular sieves. Furthermore, selective gas sensing within complex gas compositions can be achieved by rejecting molecules with kinetic diameters larger than the effective interlayer spacing. The program has main five tasks: (1) Investigate the large-scale electrodeposition of TMOs on EG by van der Waals epitaxy; (2) characterize and quantify the dominant sensing mechanisms of the synthesized heterostructures through structural, electrical, and chemical characterization; (3) assess the gas sensing performance of the 2D heterostructures with various intercalated ions through the design and fabrication of conductometric/impedimetric gas sensors, guided by density functional theory, numerical calculations, and material characterization; (4) test the sensor performance against different gas compositions and conditions by varying molecule size, temperature, pressure, and humidity; and (5) develop a predictive algorithm based on sensor output metrics to reduce possible cross-sensitivity with molecules of similar size and impedance response and integrated into a portable sensing platform capable of breath-based and environmental sensing.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.