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Issue 44, 2010
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Dielectric interlayers for increasing the transparency of metal films for mid-infrared attenuated total reflection spectroscopy

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Abstract

By depositing a continuous, thin metal film on a substrate coated with a mid-infrared (IR) transparent dielectric film that fulfils the role of an index-matching, anti-reflective coating for the metal, the transparency of the metal in the IR wavelength range can be significantly enhanced. This effect is used to yield enhanced absorption in attenuated total internal reflection infrared (ATR-IR) spectroscopy in the presence of continuous thin metal films. The main limitation of the ATR technique when using continuous metal films is the low transparency of metals, especially for infrared light. Computations and experiments show an enhancement in the absorbance of a sample in contact with the metal at certain wavenumbers when the dielectric interlayer is present. The realisation of the setup is the stratified system consisting of zinc selenide - germanium (∼1 μm) - gold (40 nm and 20 nm) using the organic solvent acetonitrile as sample. Enhancement is stronger in s- than in p-polarisation. In s-polarisation, enhancement factors of up to 4 have been observed so far in experiments, but calculations show a route to higher enhancements. In addition to the increased absorption, the absorbance spectra show interference fringes which are due to a mismatch in the real part of the refractive index of the sample in contact with the metal film compared to a reference measurement.

Graphical abstract: Dielectric interlayers for increasing the transparency of metal films for mid-infrared attenuated total reflection spectroscopy

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Publication details

The article was received on 08 Jul 2010, accepted on 28 Sep 2010 and first published on 13 Oct 2010


Article type: Paper
DOI: 10.1039/C0CP01125H
Citation: Phys. Chem. Chem. Phys., 2010,12, 14798-14803
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    Dielectric interlayers for increasing the transparency of metal films for mid-infrared attenuated total reflection spectroscopy

    M. Reithmeier and A. Erbe, Phys. Chem. Chem. Phys., 2010, 12, 14798
    DOI: 10.1039/C0CP01125H

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