Stacked Graphene Ensembles as Low-Power, Highly Reversible Gas Flow and Pressure Sensors

Abstract The ability to detect the flow of gases is critical in a number of applications such as environmental monitoring and safety, agricultural plants, automation, and the healthcare sector. Conventional metal oxide-based gas sensors typically exhibit poor stability at high operating temperatures, while polymers degrade in the presence of moisture. Two-dimensional (2D) materials such as graphene serve as promising candidates for such studies because of their large surface-to-volume ratio, ease of surface functionalization, and ability to be integrated within a three-dimensional (3D) device architecture. In particular, solution-processed graphene, nucleated into thin films via inkjet printing, offers a favorable template for gas adsorption through the largely porous microstructure characteristic of such films compared to, for example, vapor-deposited pristine and dense metal films. In this work, we report on the synthesis, fabrication, and characterization of our two-terminal contacted graphene-based device. The active channel region for the device under test (DUT), comprising loosely oriented, multilayer graphene platelets, was characterized using scanning electron microscopy, Raman spectroscopy, atomic force microscopy, X-ray diffraction, and four-point electrical probing for resistivity determination. Current modulations in the DUT revealed a strong, dynamic response to the flow of semi-inert gases, such as N2 and CO2, within a controlled ambient environment in a vacuum chamber. The cyclical, time-dependent behavior of the current, observed with each ON and OFF gas flow pulse, was also highly reversible given that the adsorption dynamics were largely governed by physisorption processes. The sensitivity of the response also increased with the gas flow rate and as the bias voltage decreased, validating the device's operational features. The results presented in this work on inkjet-printed, solution-processed graphene films suggest that their porous, network-like microstructure is ideally suited for monitoring such physical and environmental parameters useful for a wide-variety of applications.