Hyperspectral infrared nanoimaging of organic samples based on Fourier transform infrared nanospectroscopy

Abstract

Infrared nanospectroscopy enables novel possibilities for chemical and structural analysis of nanocomposites, biomaterials or optoelectronic devices. Here we introduce hyperspectral infrared nanoimaging based on Fourier transform infrared nanospectroscopy with a tunable bandwidth-limited laser continuum. We describe the technical implementations and present hyperspectral infrared near-field images of about 5,000 pixel, each one covering the spectral range from 1,000 to 1,900 cm−1. To verify the technique and to demonstrate its application potential, we imaged a three-component polymer blend and a melanin granule in a human hair cross-section, and demonstrate that multivariate data analysis can be applied for extracting spatially resolved chemical information. Particularly, we demonstrate that distribution and chemical interaction between the polymer components can be mapped with a spatial resolution of about 30 nm. We foresee wide application potential of hyperspectral infrared nanoimaging for valuable chemical materials characterization and quality control in various fields ranging from materials sciences to biomedicine.

High performance mixed matrix membranes (MMMs) composed of ZIF-94 filler and 6FDA-DAM polymer

“…For the first time membranes were characterized by noninvasive infrared scattering type scanning near field optical microscopy, which provides nanoscale-resolved chemical information that complements standard analysis methods. In the future, s-SNOM could be applied for more detailed nanoscale studies, for example of inhomogeneities, and chemical interaction, particularly at the interfaces between individual membrane components [52].…”

“…Pure polymer: pure gases vs mixed gases for 6FDA-DAM membrane To date, most of the permeation data reported in literature is for pure gases. In most cases transport behavior of gas mixtures through membranes is different from that of pure gases [52,53]. This leads to differences in pure gas and mixed gas permeabilities and selectivities.…”

“…Indeed, the infrared phase image at 1600 cm −1 does not show significant contrast. In the future, s-SNOM could be applied for more detailed nanoscale studies, for example of inhomogeneities, and chemical interaction, particularly at the interfaces between individual membrane components [52].…”

Infrared Spectroscopy and Imaging at Nanometer Scale

“…With the Fourier transform, the interferogram at each point is converted to the nano‐FTIR spectrum (Reproduced with permission from Ref. . Copyright 2017, Springer Nature).…”

“…With a broadband IR light source (such as the ones from synchrotron radiation or from IR super‐continuum laser), whole IR sSNOM spectrum can be obtained by sweeping the reference mirror in the interferometer (Figure (a) and (b)), and by the Fourier transformation (FT) of the interferogram at each tip position. Such FT‐IR‐sSNOM (also called the Nano‐FTIR) provides hyperspectral chemical map of the sample with a spatial resolution of ~10 nm . Because the scattered light can interfere with the incident light, the sSNOM has large coherent background that often generates image artifacts .…”