posted on 2022-01-10, 17:04authored byYuan Gao, D. E. Aspnes, Stefan Franzen
The molecule–plasmon interaction
is the key to the mechanisms
of surface enhanced infrared absorption (SEIRA) and surface enhanced
Raman scattering (SERS). Since plasmons are well described by Maxwell’s
equations, one fundamental treatment involves the classical interpretation
of infrared absorption and resonance Raman spectroscopies. We can
understand the molecule–plasmon interaction using electromagnetic
theory if the classical field effect on a transition dipole moment
or transition polarizability is properly described. In previous work,
we derived the Raman excitation profile of a model molecule using
a classical driven spring attached to a charged mass with a perturbative
force constant due to vibrational oscillations. In this study we generalize
the interactions of plasmons with molecules by considering the N2O asymmetric stretch SEIRA signal on a Dy doped CdO (CdO:Dy)
film. This semiconductor has tunable plasmon dispersion curves throughout
the near-and mid-infrared that can interact directly with vibrational
absorption transitions. We have demonstrated this using the Kretschmann
configuration with a CaF2 prism and a MgO substrate. The
model predicts the phase behavior of SEIRA. The calculated enhancement
factor relative to an Au control is 6.2, in good agreement with the
value of 6.8 ± 0.5 measured under the same conditions.