Nanocomposite thin films of gold nanoparticles embedded in yttria-stabilized zirconia for plasmonic-based harsh environment gas detection

Increased health concerns due to the emission of gases linked to the production of tropospheric ozone by petroleum based fuel burning engines has resulted in the codification of more stringent emissions regulations domestically. Emissions regulations on commercial jetliners are one of the areas to be met with stricter standards. Currently there is not a sensing technology that can detect the emissions gases in the exhaust stream of a jet turbine engine with lower detection limits that meet these standards.;The localized surface plasmon resonance (LSPR) of noble metal nanoparticles embedded in dielectric matrices is an optical response that can be extremely sensitive to many environmental parameters. Nanocomposites of Au nanoparticles embedded in yttria-stabilized zirconia (Au-YSZ) are an ideal case study for these plasmonic materials. Using a metal oxide matrix with oxygen ion vacancies, such as YSZ, allows one to finely tune the local environmental charge of the embedded metal nanoparticles upon varying the oxygen and hydrogen content of the gas exposure mixture. After gas exposure data is collected in the form of optical absorption spectra, the LSPR spectra due to the Au nanoparticles embedded in the YSZ matrix undergo automated Lorentzian and Drude model fitting for calculating fundamental charge exchange and plasmonic dampening effects versus gas exposure concentration. These titration experiments have been performed for Au-YSZ nanocomposites exposed to O2, H2, NO 2, and CO in N2 backgrounds at 500°C and equilibrium data has been acquired for both the average charge per Au nanoparticle and the scattering frequency of the plasmons over a variety of exposure conditions. One paramount result made possible by this plasmonic based gas detection by Au-YSZ nanocomposite thin films was a repeatable 5 ppm lower detection limit towards NO2 in air at 500°C. In comparing the charge exchange observed using both the fitted exposure data and an electrochemical model, insight into reaction energies pertaining to metal nanoparticle induced catalytic reactions has be gained. In addition to measuring and modeling charge exchange phenomena via shifts in the LSPR peak position, the electron scattering frequency, also known as the dampening parameter is modeled as arising directly from inelastic scattering from electron states within the YSZ matrix, the magnitude of which being proportional to band bending or work function shifts within the YSZ. Lastly, focus has been placed on the deposition of Au-YSZ nanocomposites with varied average grain size to determine the influence of Au nanoparticle size on chemical reactions occurring within the Au-YSZ thin films and to further the development of electrochemical models.