An ultimate goal in modern chemistry and materials science is the non-invasive chemical mapping of materials with nanometer-scale resolution. A variety of high-resolution imaging techniques exist (e.g. electron microscopy or scanning probe microscopy), however, their chemical sensitivity cannot meet the demands of modern chemical nano-analytics. Optical spectroscopy, on the other hand, offers high chemical sensitivity but its resolution is limited by diffraction to about half the wavelength, thus preventing nanoscale-resolved chemical mapping.

Nanoscale chemical identification and mapping of materials now becomes possible with nano-FTIR, an optical technique that combines scattering-type scanning near-field optical microscopy (s-SNOM) and Fourier transform infrared (FTIR) spectroscopy. By illuminating the metalized tip of an atomic force microscope (AFM) with a broadband infrared laser, and analyzing the backscattered light with a specially designed Fourier Transform spectrometer, the researchers could demonstrate local infrared spectroscopy with a spatial resolution of less than 20 nm. “Nano-FTIR thus allows for fast and reliable chemical identification of virtually any infrared-active material on the nanometer scale,” said Florian Huth, who performed the experiments.

An important aspect of the advancement, with enormous practical relevance, is that the nano-FTIR spectra match extremely well with conventional FTIR spectra, while the spatial resolution is increased by more than a factor of 300 compared to conventional infrared spectroscopy. “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” concluded Rainer Hillenbrand, leader of the Nanooptics group at nanoGUNE.