Jul 27, 2012 |
Nano-FTIR - A new era in modern analytical chemistry
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(Nanowerk News) Researchers from the nanoscience research center NanoGUNE (San Sebastian, Spain), the university of Munich (LMU, Germany) and Neaspec GmbH (Martinsried, Germany) present a new instrumental development that solves a prime question of materials science and nanotechnology: how to chemically identify materials at the nanometer scale (see paper in Nano Letters: "Nano-FTIR Absorption Spectroscopy of Molecular Fingerprints at 20 nm Spatial Resolution").
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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.
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Chemical identification of nanoscale sample contaminations with nano-FTIR. In the topography image (left), a small sample contaminant (B) can be found next to a thin film of PMMA (A) on a Si substrate (dark region). In the mechanical phase image (middle) the contrast already indicates that the particle consists of a different material than the film and the substrate. Comparing the nano-FTIR absorption spectra at the positions A and B (right panel) with standard IR databases reveals the chemical identity of the film and the particle. Each spectrum was taken in 7 minutes with a spectral resolution of 13 cm-1.
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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”, says Florian Huth, who performed the experiments.
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An important aspect of 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” concludes Rainer Hillenbrand, leader of the Nanooptics group at nanoGUNE.
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For example, nano-FTIR can be applied for the chemical identification of nanoscale sample contaminations. Fig. 1 shows AFM images of a PMMA film on a Si 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, the contamination can be identified as a PDMS particle.
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The CIC nanoGUNE Consolider, nanoGUNE in short, is the Basque nanoscience and nanotechnology research center, inaugurated in 2009 in Donostia – San Sebastián, Spain. Neaspec GmbH has been established in 2007 as a spin-off from the Max Planck Institute of Biochemistry (Martinsried, Germany) and is the first supplier of commercial scattering-type near-field optical microscopes.
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