Surface enhanced infrared absorption (SEIRA) is of interest for chemical sensing applications and has been demonstrated with plasmonic materials, which exhibit broad resonance bands as a result of fast electron scattering rates. Surface phonon polaritons (SPhPs) however, depend on lower loss phonon optical properties of polar dielectric materials, which results in narrow resonance bands. In particular, our group is investigating polar dielectric inorganic molecular crystals that have mid-IR Reststrahlen bands, frequency ranges where the crystals’ optical constants resemble metals and can support SPhP resonances. Currently, our efforts are focused on studying the optical properties of W(CO)<sub>6</sub> and calcite (CaCO<sub>3</sub>) molecular crystals. Calcite has been found to be hyperbolic, meaning that the sign of the real part of the dielectric function is either positive or negative depending on the polarization of the incident light. We are also experimenting with using a helium ion microscope to nanostructure the surface of these polar dielectric materials in order to generate SPhPs for sub-diffraction optical confinement of mid-IR incident light. The results of these studies will allow us to better understand how to tune SPhPs in a broader spectral range with different inorganic materials and provide a basis for exploring how these resonances interact with other chemical systems through enhanced spectroscopies and energy transfer.

Expanding the scope of surface phonon polaritons to new materials

2019 Spring National Meeting

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