nano-FTIR

Setup for synchrotron-based s-SNOM (DOI: 10.1002/adom.201901091) Copyright 2018, Optical Society of America

In s-SNOM, an AFM tip is used to confine and focus the IR light interaction on a sample via its scattered reflection. When the tip is brought very close to the sample surface, the IR light probes the sample in the near-field region.

The scattered light can be detected and contains information about the sample's local optical properties. In particular, the signal amplitude is related to the sample reflectivity, whereas the phase response approximately corresponds to the IR absorption spectrum.

In the experimental approach of the nano-FTIR setup, an asymmetric interferometer is used. The AFM tip and sample are located in one of the interferometer arms. The scattered light is recombined with a reference beam at the detector. The interferogram corresponds to the detector signal as a function of reference mirror position: Fourier Transform is then applied to obtain phase and amplitude.

• Highest spatial resolution up to 10 nm
• Surface-sensitive technique with ~100s nm penetration depth (or thin samples on reflective surfaces)
• Spectral range dictated by the detectors and tip geometry
• Resulting phase spectrum as linear approximation of absorption
• Reference spectrum from well-defined material required

For life sciences, this technique is suitable for thin biological preparations onto reflective substrates and studies in the fingerprint region

Publications on the technique:

• Keilmann, Fritz, and Rainer Hillenbrand. "Near-field microscopy by elastic light scattering from a tip." Philosophical Transactions of the Royal Society of London. Series A: Mathematical, Physical and Engineering Sciences 362.1817 (2004): 787-805.
• Bechtel, Hans A., et al. "Synchrotron infrared nano-spectroscopy and-imaging." Surface Science Reports 75.3 (2020): 100493.
• Mester, Lars, et al. "Subsurface chemical nanoidentification by nano-FTIR spectroscopy." Nature communications 11.1 (2020): 3359.

Publications on projects at B22:

• Synchrotron nano-FTIR spectroscopy for probing anticancer drugs at subcellular scale - Luis A. E. Batista De Carvalho, Gianfelice Cinque, Ana L. M. Batista De Carvalho, Joana Marques, Mark D. Frogley, Hendrik Vondracek, Maria Paula M. Marques - Sci Rep, DOI: 10.1038/s41598-024-67386-y