You say you want resolution: Nano-FTIR

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  • Published: Sep 1, 2012
  • Author: David Bradley
  • Channels: Infrared Spectroscopy
thumbnail image: You say you want resolution: Nano-FTIR

Going nano on spectroscopy

An optical technique that combines Fourier transform infrared (FTIR) spectroscopy and scattering-type scanning near-field optical microscopy (s-SNOM) now allows nanoscopic quantities of materials to be identified chemically and mapped. Credit: ACS 

An optical technique that combines Fourier transform infrared (FTIR) spectroscopy and scattering-type scanning near-field optical microscopy (s-SNOM) now allows nanoscopic quantities of materials to be identified chemically and mapped. The technique of nano-FTIR developed has been developed by scientists from the nanoscience research centre NanoGUNE in San Sebastian, Spain, the University of Munich, LMU, Germany and Neaspec GmbH in Martinsried, Germany.

Writing in the American Chemical Society journal Nano Letters, the team explains how the new instrumentation thus solves one of the big problems in materials science and nanotechnology.

The non-invasive identification of materials and the mapping of their features on the nanometre scale of resolution is a critical problem in modern materials science. Various approaches have been taken to address this problem including the development of high-resolution imaging techniques, including electron microscopy and scanning probe microscopy. Unfortunately, while these techniques are powerful in their own right, their low chemical sensitivity does not meet the demands of modern analytical chemistry that must today function on the nanoscale. Conversely, optical spectroscopy offers suitably high chemical sensitivity but it is limited to the diffraction boundary, approximately half the wavelength of light, which means it is not a viable technique for nanoscale mapping.

The European team has now combined the advantages of both approaches and sidestepped their limitations in nano-FTIR by bringing together sensitivity and resolution in a single hybrid technique. The team explains that by illuminating the metalized tip of an atomic force microscope (AFM) using a broadband infrared laser they can and analyse the backscattered light with a unique FTIR spectrometer. This allowed the researchers to localise the infrared spectra obtained with a spatial resolution of below 20 nanometres. 20 nm is equivalent to a probed volume of down to 10 zeptolitres.

"Nano-FTIR thus allows for fast and reliable chemical identification of virtually any infrared-active material on the nanometre scale," explains team member Florian Huth. Importantly, the nano-FTIR spectra obtained correlate extremely well with the conventional FTIR spectra for the same materials in bulk but the resolution is a factor of 300 times greater than with conventional infrared spectroscopy. "Nano-FTIR can thus make use of standard infrared databases of molecular vibrations to identify organic materials in ultrasmall quantities and at ultrahigh spatial resolution," the team says.

Unique analytical tool

Rainer Hillenbrand, who heads the Nanooptics group at nanoGUNE adds that, "The high sensitivity to chemical composition combined with ultra-high resolution makes nano-FTIR a unique tool for research, development and quality control in polymer chemistry, biomedicine and pharmaceutical industry."

The nano-FTIR might now be used to identify chemical contamination in polymer films and other chemical systems. For instance, it is possible to identify nanoscale sample contaminations in AFM images of a poly(methylmethacrylate), PMMA, film on a silicon surface. The AFM phase contrast betrays the presence of contaminants in regions of 100 nm across, but it is the nano-FTIR spectra that allow the team to focus on the centre of this region and so identify the contaminant as a particle of PDMS, polydimethylsiloxane.

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Article by David Bradley

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

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