Plasmonic sensors for applications in catalysis and art conservation

The work described here includes both fundamental and application based studies centered around the use of plasmonic sensors. Fundamental studies focus on probing the optical properties of nanosphere lithography (NSL) fabricated Ag nanoparticles, while surface-enhanced Raman spectroscopy (SERS) sensors are applied to identify and characterize artists' red dye and red lake pigments. Experiments were conducted to further our understanding of the optical properties and thermal stability of NSL fabricated Ag nanoparticles in order to design the best sensor for a given system. Because these nanoparticles are extremely sensitive to their dielectric environment, atomic layer deposition (ALD) was used to fabricate highly uniform, ∼1 A, monolayers of Al2O 3 in order produce a high resolution study of the short and long range distance dependence of the localized surface plasmon resonance (LSPR) of these nanoparticles. Because Ag triangular nanoparticles will anneal into hemispheres at elevated temperatures (200°C and above), NSL fabricated Ag nanoparticles were coated with thin layers (0.2 - 1.0 nm) of ALD Al2O3. These new thermally stable nanoparticles have potential to be used to conduct in situ monitoring of model catalytic reactions by SERS.; Plasmonic sensors were applied in the field of art conservation. Both silver island film (AgIF) and silver film over nanosphere (AgFON) SERS substrates were successfully used to identify and characterize artist's red dyes and red lake pigments. In the past, Raman spectroscopy has been successfully employed to identify many pigments and modern synthetic dyes. Unfortunately, red lake pigments are both poor Raman scatterers and extremely fluorescent, therefore there has been few Raman spectra collected for many of these materials. SERS has been a successful technique because it not only enhances the Raman effect; but, also quenches fluorescence, resulting in detailed vibrational information that can be used to correctly identify red lakes and natural red dyestuffs. Fundamental and application based studies of plasmonic sensors are equally important so that the best sensor can be designed for the desired application.