Scattering-type Scanning Near-field Optical Microscopy (s-SNOM) is a scanning probe approach to optical microscopy and spectroscopy bypassing the ubiquitous diffraction limit of light to achieve a spatial resolution below 20 nanometers. s-SNOM employs the strong confinement of light at the apex of a sharp metallic AFM tip to create a nanoscale optical hot-spot. Analyzing the scattered light from the tip enables the extraction of the optical properties (dielectric function) of the sample directly below the tip and yields nanoscale resolved images simultaneous to topography [1]. In addition, the technology has been advanced to enable Fourier-Transform Infrared Spectroscopy on the nanoscale (nano-FTIR) [2] using broadband radiation (i.e. a mid-IR supercontinuum fs-laser) in the mid-IR spectral range. Applying nano-FITR near-field spectroscopy to measure the spectroscopic signature enables identification of i.e. polymers at a spatial resolution given only by the size of the AFM tip at unprecedented sensitivity [3]. For example, nano-FTIR spectroscopy of a self-assembled Polyethylene-Oxide (PEO) monolayer enables unambiguous material identification of sub-micron sized structures by comparing IR absorption lines measured by conventional FTIR with near-field spectroscopic signatures (Fig. 1, right). Chemical mapping at 1123cm-1 is sensitive to the material-characteristic absorption of PEO, which allows to selectively highlight nanoscale PEO structures with thickness of only 11nm and to differentiate between mono- and bilayer structures (Fig. 1, left). Results presented demonstrate that nano-FTIR can be an ideal analysis method to characterize complex material systems and to identify polymer materials at the nanoscale spatial resolution and unmatched sensitivity.

nano-FTIR based identification & characterization of polymers at 10nm resolution

2019 Spring National Meeting

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