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Laser Structuring of Graphene Oxide for PHOTOtronic SENSors and Nanoscale Characterization (PHOTOSENS)

Subject Area Synthesis and Properties of Functional Materials
Electronic Semiconductors, Components and Circuits, Integrated Systems, Sensor Technology, Theoretical Electrical Engineering
Microsystems
Term from 2020 to 2023
Project identifier Deutsche Forschungsgemeinschaft (DFG) - Project number 430426661
 
Final Report Year 2024

Final Report Abstract

This project explored the application of laser technology to fine-tune the properties of graphene oxide (GO) materials for enhanced sensing applications. The goal was to control the work function and bandgap of reduced graphene oxide (rGO) layers using precise laser and material settings. We also investigated electron transport and conduction mechanisms for different patterned films to improve sensitivity and explore how tuning dielectric properties in microstructures affects the adsorption of chemical species and their resulting properties. To measure the work function of laser-patterned rGO electrodes, Raman spectroscopy revealed that optimal reduction occurs at 30 mW IR fs laser power. X-ray photoemission spectroscopy (XPS) measurements indicated that varying the pattern speed at this fixed power shifts the work function between 4.95 and 5.05 eV. The work function can also be tuned by the cw laser power range (660-960 mW) in the range of 4.85 to 5.1 eV. The bandgap of GO films decreases from 3.4 to 1.6 eV with increasing laser power (660 – 960 mW) until it saturates. However, quantitative evaluation is challenging due to the complex material structure and ablation at higher laser intensity. The fluctuation-induced tunneling (FIT) model best explains the temperature dependence of the resistance in laser-reduced rGO. Miniaturized structures were also developed, including fully reduced GO sensors and interdigitated electrode (IDE) structures, with IDEs showing higher sensitivity for humidity and volatile organic compound sensing. The project further explored creating heterostructures like GO-rGOx and rGOx-rGOy junctions using different laser reduction parameters. These structures enhance photosensitivity and generate a broad spectral photoresponse. In addition, we examined the work functions and bandgap properties of symmetric and asymmetric electrodes and found that rGOx-rGOy heterostructures exhibit asymmetrical I-V characteristics with high photoresponsivity of >3 A/W at 650 nm (red) wavelength. A van der Waals barrier formed heterostructures with negative differential resistance, where the photothermoelectric effect dominated, generating significant current and voltage under laser light. Strain sensitivity tests revealed that the orientation of laser writing significantly affects the rGO gauge performance where a gauge factor (GF) of 16 was obtained. Increased piezophototronic sensitivity is correlated to the tuning of the optical properties.

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