Chemical identification at nanometre scale

ELECTRON microscopy and scanning probe microscopy offer the scientific researcher powerful high-resolution imaging at the nanometre scale, but are poor at identifying the chemical composition of the structures they image. Spectroscopy offers powerful chemical identification, but has resolution limited to about half a wavelength of light – which means it is poor at nanoscale chemical mapping.

Now researchers from Spain and Germany reckon they have cracked this previously-intractable problem. They say their new approach, called nano-FTIR, will usher in a new era in analytical chemistry by chemically identifying materials at the nanometre scale.

Nano-FTIR is an optical technique that combines scattering-type scanning near-field optical microscopy (s-SNOM) and Fourier transform infrared (FTIR) spectroscopy.

Nanoscale sample contamination identified with nano-FTIR. The topography image (left) shows a contaminant (B) next to a thin film of PMMA (A) on a Si substrate (dark region). The contrast in the mechanical phase image (middle) shows that the particle is a different. Comparing the nano-FTIR absorption spectra reveals the chemical identity of the film and the particle. Each spectrum was taken in seven minutes with a spectral resolution of 13cm-1.

By illuminating the metalised tip of an atomic force microscope (AFM) with a broadband infrared laser, and analysing the backscattered light with a specially designed Fourier Transform spectrometer, the researchers report that they can achieve highly-localised infrared spectroscopy with a spatial resolution of less than 20nm.

One aspect the researchers highlight is that the nano-FTIR spectra are a good match to conventional FTIR spectra, while the spatial resolution is about 300 times better than conventional infrared spectroscopy.

Writing in Nano Letters, the scientists from the NanoGune research centre in San Sebastian, Spain, the university of Munich, Germany, and German company Neaspec, say this new tool offers much potential for research, development, and quality control in polymer chemistry, biomedicine and pharmaceutical industry.


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