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Infrared (IR) Spectroscopy: Overview

Infrared (IR) Spectroscopy: Overview

When electromagnetic radiation passes through a material, atoms or molecules transition from a lower to a higher energy state by absorbing radiation corresponding to the energy difference between the two states. The absorption of infrared (IR) radiation causes transitions between vibrational energy levels in a molecule. Therefore, IR spectroscopy is a useful analytical tool for determining the molecular structure of molecules.
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IR Frequency Region: Fingerprint Region

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IR Spectrum

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Attenuated total reflectance (ATR) infrared spectroscopy is a powerful analytical technique used to study the composition of materials. It is widely employed in chemistry, materials science, forensic science, and other fields where sample characterization is required. ATR has several advantages over traditional transmission IR spectroscopy, including the requirement of little to no sample preparation and the ability to analyze a wide range of samples.
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In situ FTIR Spectroscopy as a Tool for Investigation of Gas/Solid Interaction: Water-Enhanced CO2 Adsorption in UiO-66 Metal-Organic Framework

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Published on: February 1, 2020

Substrate-enhanced infrared near-field spectroscopy.

Javier Aizpurua¹, Thomas Taubner, F Javier García de Abajo

¹Donostia International Physics Center, P. Manuel Lardizabal 4, 20018 San Sebastián, Spain. aizpurua@ehu.es

|June 11, 2008

Summary

We found that using strongly reflecting substrates significantly enhances infrared scattering-type near-field optical microscopy (s-SNOM) signals. This improvement allows for ultra-sensitive spectroscopy of thin layers and biomolecules.

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Area of Science:

Nanophotonics
Infrared Spectroscopy
Surface Science

Background:

Scattering-type near-field optical microscopy (s-SNOM) is a powerful technique for nanoscale optical characterization.
Understanding the influence of substrate reflectivity on s-SNOM signals is crucial for optimizing measurements.
Previous studies have not fully explored the substrate's role in enhancing spectral signals.

Purpose of the Study:

To theoretically and experimentally investigate the effect of substrate reflectivity on s-SNOM signals.
To explore the enhancement of polymer vibrational spectra using different substrates.
To demonstrate the potential for ultra-sensitive spectroscopy of thin layers and biomolecules.

Main Methods:

Solving electromagnetic scattering of a dipole near a layered planar sample.
Performing spectral s-SNOM measurements on a PMMA layer on weakly (Si, SiO2) and strongly (Au) reflecting substrates.
Calculating scattered fields for resonant tip-substrate interactions.

Main Results:

A significant enhancement of the polymer vibrational spectrum was observed on strongly reflecting substrates.
Theoretical predictions of this enhancement were experimentally confirmed.
Resonant tip-substrate interactions led to dramatic signal amplitude and spectroscopic contrast enhancement.
Spectral line shapes were observed to change under resonant conditions.

Conclusions:

Strongly reflecting substrates can dramatically enhance s-SNOM signals and spectroscopic contrast.
This enhancement enables ultra-sensitive near-field infrared spectroscopy.
The technique holds promise for analyzing monolayers and biomolecules with high sensitivity.