EAGER: Amorphous Photonic NanoMembranes for Broadband Chemical Sensing

Ohio University, Athens OH

Investigators

Abstract

Project Motivation While there has been extensive development on integrated sensors in the near-IR region due to the maturation of Si, SOI, and III-V materials, these technologies are not easily translated into the visible and near-UV regions which are critical for the detection of many chemicals of environmental and security interest. This project focuses on the use of wide bandgap, amorphous materials, specifically, amorphous zinc oxide (a-ZnO), amorphous hafnium oxide (a-HfO2) and amorphous beryllium zinc oxide (a-BeZnO), in the development of broadband chemical sensors operating at critical absorption lines spanning the near-UV (200 nm) to the near-IR (1.5 µm). These amorphous materials are deposited at low temperature (0 to 100ºC), are substrate-independent, and have chemical etch selectivities compatible with most dielectric, III-V, and Group-IV materials. The architecture employed for this research is a nanoscale membrane (typically 40-100 nm thick) that supports a guided low optical overlap mode (LOOM) - an optical mode in which approximately 1% of the electric field is confined to the lossy core region. The resulting extended mode has a greatly enhanced overlap with the analyte, resulting in a device sensitivity (~70%) that is over an order of magnitude higher than current high-performance, dielectric evanescent wave sensors (~2%) as modeled by analytical and finite element methods. Intellectual Merits The proposed project has two core objectives within the one-year time frame to demonstrate the advantages of this sensing approach, (1) the demonstration of broadband LOOM propagation in amorphous nanostructured membrane waveguides at the critical absorption lines 1513 nm and 598 nm (NH3), 357 nm (TiCl4), and 220 nm (PCl3); and (2) the demonstration of the enhanced LOOM sensing of NH3 by the use of an integrated Mach-Zehnder interferometer. Highly sensitive, integrated sensors that utilize a single-material, single-design platform that span the spectral range of 200 nm to 1600 nm are a potentially disruptive technology that would displace the current need to heterogeneously integrate several different materials and architectures. In addition, the ability to achieve compact multi-point sensing, utilizing a CMOS-compatible process, can greatly enhance the detection of specific gaseous and aqueous agents, thereby reducing false positives. Furthermore, the extended modal profile and dispersive insensitivity of these designs may also lead to the development of highly efficient SERS probes. Our modeling has also shown that the extension of this technology into the THz region, where integrated technologies are difficult to develop, can also be attained. Broader Impacts Within the Appalachian Ohio region, there is a strong need for the monitoring of gaseous and aqueous contaminants due to coal-fired plant emissions and agricultural runoff. Compounds such as reactive gaseous mercury (RGM), sulfur dioxide (SO2), and zinc are just a few examples of difficult-to-detect materials with absorption signatures in the visible and near-UV. This research sets a baseline approach to develop effective technologies for their detection. The PI for this project works with several undergraduate and graduate students from the SE Ohio area that have a strong concern for these issues. This project will support two graduate students, one of whom is from an underrepresented, minority group.