Epsilon-Near-Zero Plasmonic Resonances For Surface Enhanced Infrared Absorption Spectroscopy

Surface plasmons have important applications in surface-enhanced infrared absorption(SEIRA)spectroscopy because of their strong localized field enhancement.However,due to the dramatically increasing permittivity of noble metals in the mid-infrared frequency range,the quality factor of plasmonic resonances drops prominently,and the full width at half maximum(FWHM)is usually very large.SiO2,with the permittivity close to zero near its longitudinal optical phonon frequency,is a natural epsilon near zero(ENZ)material.When a noble metal plasmonic antenna is located on the ENZ material,the response of the plasmonic antenna,especially the localization of the plasmonic field and the quality factor of the plasmonic resonance,will be greatly enhanced.Therefore,in this thesis,we will use SiO2 as the ENZ substrate to introduce ENZ plasmonic mode for SEIRA applications.In this thesis,we have designed the ENZ plasmonic modes of both rod antenna arrays and U-shaped antenna arrays and investigated their applications in SEIRA.The main results are as follows:(1)We have fabricated gold rod antenna arrays on the SiO2 substrate,excited the ENZ plasmonic mode,observed the "pinning effect",and found the effect of antenna’s period in the short axis direction on the "pinning effect".In addition,we have tuned the ENZ plasmonic mode by the size of the rod antenna,and successfully demonstrated SEIRA with the ENZ plasmonic mode.(2)We have designed gold U-shaped antenna arrays on the SiO2 substrate to further enhance the SEIRA sensitivity.Compared to rod antennas,the ENZ plasmonic mode of U-shape antennas can be easier tuned by their size.In the SEIRA experiments,we have observed the coupling induced mode splitting and anti-crossing between the ENZ mode and the PMMA molecular vibrations.Such coupling depends on the PMMA layer thickness and reaches the strong coupling regime at～200 nm.Furthermore,the coupling strength is also sensitive to the polarization angle of the incident light.This thesis shows the SEIRA applications of ENZ plasmonic resonances and demonstrates strong coupling between plasmonic resonances and molecular vibrations in the mid-infrared frequency range.Our results provide new ideas for ultrasensitive midinfrared spectroscopy.