17th International Meeting on Chemical Sensors - IMCS 2018 64 DOI 10.5162/IMCS2018/GS1.2 Nanoheterostructure Metal Oxide Gas Sensors: Opportunities and Challenges Sheikh A. Akbar 1 , Derek R. Miller 1 , Mohamad A. Al-Hashem 1 , Priyanka Karnati 1 , Janine Walker 1 , Patricia A. Morris 1 1 Department of Material Science and Engineering, The Ohio State University, Columbus, OH 43210, United States Corresponding Author: akbar.1@osu.edu Abstract The use of nanoheterostructures as gas sensors has shown the potential to address issues such as gas selectivity or sensitivity in metal-oxide gas sensors although many outstanding challenges remain that inhibit a bottom-up approach to their design. As more complex heterostructures are used, the mechanisms governing their behavior become more ambiguous requiring precise material and electrical characterization techniques to be used. High spatial resolution microscopy has demonstrated the ability to characterize the band structure and defect states in SnO 2 nanomaterials revealing the complex nature of mid-gap defect states present. Impedance spectroscopy on single and multi-nanowire SnO 2 gas sensors has demonstrated an ability to discriminate between different contributions to sensor response and reveal the underlying mechanisms involved. These techniques are expected to help address outstanding questions to explain the role that defects and heterostructure types have in the sensing process and deconvolute the complex relationships involved to uncover the underlying mechanisms. Additionally, an Open access Database Of Resistive type gas Sensors (ODORS) that is under development is expected to greatly enhance productivity in the field by enabling more informed research studies and presenting new perspectives. Key words: Nanomaterials, Heterostructures, Impedance Spectroscopy, Defects, Synergistic Effects Metal Oxide Nanostructure Characterization Metal oxide nanostructures have been extensively characterized using the high spatial resolution techniques of STEM VEELS [1] and STEM-CL [2] demonstrating the ability to directly characterize the band structure of nano- heterostructures and the complex mid-gap defect states present in SnO 2 nanomaterials (Fig. 1). Given the large number of studies that have been published in the field and the variability in results, a clear understanding of the role and behavior of defects in gas sensing in lacking. To fully understand the role of defects and how they behave under real conditions, careful analysis of the electrical characteristics of these nanostructures under different conditions must be carried out to understand how variables such as annealing temperature, cooling rate or oxygen in/out diffusion affect the behavior of nanostructured metal oxide gas sensors. Impedance Spectroscopy of Nanostructures Impedance measurements carried out on single nanowire (SNW) and multi-nanowire (MNW) SnO 2 sensors revealed important information regarding the gas sensing mechanisms of these sensors [3]. Careful circuit analysis revealed that the nanowire junctions in MNW sensors had a greater contribution to the sensors response compared to the conduction channel modulation while I-V characteristics of the SNW sensors were shown to depend on NW diameter and susceptible to O 2 in-diffusion Fig.1.Defect band structure in a few SnO 2 nanomaterials [2]. Reprinted with permission.