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Observation of the enhanced infrared absorption of p-nitrobenzoate on Ag island films with an ATR technique

Abstract

By the use of an ATR technique we have found that the infrared absorption of p-nitrobenzoate, formed on Ag island film about 5 nm thick, is enhanced by a factor of the order of 10. Only vibrational modes involving a change in the dipole moment of the benzoate ion perpendicular to the macroscopic Ag surface are enhanced by p-polarized radiation alone, indicating the electric field of the evanescent wave polarized perpendicular to the Ag surface plays a dominant role in the infrared excitation process. A monolayer of stearic acid deposited on a Ag underlayer 5nm thick gave another example of the enhancement. Although the mechanism of enhancement is not fully elucidated, the existing model based on the collective electron resonances of Ag islands is not applicable to the present case, since it predicts the electron resonance can be excited irrespective of polarization state of infrared beam.

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Hatta, A., Ohshima, T. & Suëtaka, W. Observation of the enhanced infrared absorption of p-nitrobenzoate on Ag island films with an ATR technique. Appl. Phys. A 29, 71–75 (1982). https://doi.org/10.1007/BF00632429

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