Optical microscopy, spectroscopy duo IDs materials at the nanoscale

An international team of researchers from NanoGUNE (San Sebastian, Spain), Ludwig Maximilian University (LMU; Munich, Germany), and Neaspec GmbH (Martinsried, Germany) have developed an optical instrument that can chemically identify materials at the nanometer scale. The work shows promise for research, development, and quality control in biomedicine and the pharmaceutical industry.

Dubbed nano-FTIR, their instrument 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," says Florian Huth, who performed the experiments.

Nano-FTIR chemically identifies nanoscale sample contaminations, as shown in the AFM images of a polymethylmethacrylate (PMMA) film on a silicon surface. While the AFM phase contrast indicates the presence of a 100 nm size contamination, the determination of its chemical identity remains elusive from these images. Using nano-FTIR to record a local infrared spectrum in the center of the particle and comparing it with standard FTIR database spectra, it identifies the contamination as a polydimethylsiloxane (PDMS) particle, a type of silicone.

An important aspect of the work 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.

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