Optical detection of adsorbed CO$_{2}$ and other gases on ferroelectric surfaces using second harmonic generation (SHG)

Due to their polar surfaces, ferroelectrics may provide an ideal way to detect and collect gas molecules, useful for applications such as gas sensing and pollution mitigation. Since ferroelectric materials have a high reliability (at least 10$^{9}$ switching cycles) these sensors could be used for prolonged periods of time without failure. Second harmonic generation (SHG) allows us to determine the spatial orientation of surface adsorbates and to monitor in realtime the kinetics of adsorption/desorption. In preliminary experiments we see a variation of SHG signal from the surface of PbZrTiO$_{3}$ (PZT) (100 nm film 20\% Zr, 80\% Ti) when dosed with 1 atm of N$_{2}$ or CO$_{2}$. There is a 21\% increase in signal when dosed with N$_{2}$ with respect to signal in vacuum and there is a 19.9\% increase in signal when dosed with CO$_{2}$ with respect to signal in vacuum. Further studies will be performed to determine the orientation of these molecules on the surface of this device. Experiments will also be performed while polarizing the device with an external electric field to determine the effect of polarization on adsorption/desorption of molecules.