Scientists from NanoGUNE, Neaspec and the University of Munich have developed a novel instrument that can perform nanoscale mapping and chemical identification of materials.
Fig. 1: 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.
The researchers have devised an optical technique called nano-FTIR that integrates Fourier transform infrared (FTIR) spectroscopy and scattering-type scanning near-field optical microscopy (s-SNOM). By using a broadband infrared laser to illuminate an atomic force microscope (AFM)’s metalized tip and a custom-designed Fourier transform spectrometer to explore the backscattered light, the researchers were able to demonstrate a local infrared microscope that have below 20 nm spatial resolution.
Florian Huth, who conducted the experiments, informed that nano-FTIR enables rapid and reliable nano-scale chemical identification of almost any infrared-active material. A significant feature of practical application is the exceptional matching similarity between the nano-FTIR spectra and traditional FTIR spectra, while there is an increase in the spatial resolution by a factor of over 300 when compared to traditional infrared spectroscopy.
Rainer Hillenbrand, who is the Head of NanoGUNE’s Nanooptics group, stated that with a combination of ultra-high resolution and high sensitivity towards chemical composition, nano-FTIR is a novel tool to facilitate research, advancement, and quality control in pharmaceutical, biomedicine and polymer chemistry industry.
For instance, nano-FTIR can be used for the chemical identification of sample contaminations at the nanoscale. Fig. 1 illustrates AFM pictures of a PMMA film over a silicon surface. Although the AFM phase contrast shows the presence of a contamination of 100 nm size, it is not possible to detect the chemical identity of the contamination from these images. However, the use of nano-FTIR to document a local infrared spectrum at the particle’s center and subsequent comparison of the spectrum with typical FTIR database spectra identified the contamination as a PDMS particle.