Near-field enhancements and surface plasmon polaritons with multifunctional oxide thin films

The thickness of multifunctional oxide films directly affects the localized enhancement of the electromagnetic field and hence is a key factor for realizing novel photonic or optoelectronic devices. To this end, we theoretically exploit the principle of tip-enhanced Raman spectroscopy on the surface of multifunctional oxide films (bismuth ferrite and barium titanate) on a gold substrate. An electromagnetic field enhancement of up to 10(4) in close proximity of the tip apex was obtained. The good agreement between simulation and experiment of spatial resolution of the tip supports the validity of our model. By investigation of surface plasmon polaritons that propagates at the interface between the multifunctional film and the gold substrate, we demonstrated a thickness dependent propagation length and amplitude. This study indicates a critical thickness of the films above which neither a considerable near-field nor a tip-mediated excitation are observed. This confirms the validity, promise, and power of tip-enhanced Raman spectroscopy technique for the analysis of various electro-optic materials.