GEC Student Excellence Award Finalist Presentation - Combining in operando FTIR and Raman to investigate the plasma-surface interaction

Non-thermal plasmas provide a pathway towards the sustainable production of chemicals using renewable energy sources instead of heat. While promising, there is still a lack of fundamental understanding of how photons, electrons, and ions from the plasma interact with catalyst surfaces and adsorbates. Here we expose an organic monolayer to an argon plasma and carry out in operando FTIR and Raman measurements. We choose Phenyl Phosphonic Acid (PPA) as molecular tracer because of its strong response in both FTIR and Raman measurements. PPA was applied onto alumina thin films grown on top of a nanostructured silver substrate. The nanostructured silver substrate enhances the Raman response of the system, enabling the detection of Raman peaks from aromatic benzene ring (1010 cm^-1) even under plasma irradiation. We find that the molecule vibrational temperature can exceed the substrate temperature by 80 K even at low plasma input power. We perform temperature programmed desorption measurements using FTIR to measure the binding energy between PPA and alumina, and we measure a significant drop in binding energy under plasma exposure. Additional characterization of the plasma via a double probe will be presented, to correlate the plasma properties with the FTIR and Raman measurements. This work suggests that the localized deposition of energy at plasma-exposed surfaces can increase significantly the surface vibrational temperature of adsorbates.