nano-FTIR employs an externally IR-illuminated sharp metallic AFM tip to create a nanoscale hot-spot at its apex. The optical tip-sample near-field interaction is determined by the local dielectric properties (refractive index) of the sample. Detection of the elastically tip-scattered light simultaneous to AFM imaging yields nanoscale resolved near-field images. Utilizing broadband laser sources like a mid-IR supercontinuum laser for tip illumination enables near-field spectroscopic measurements at nanometer scale spatial resolution with unprecedented signal quality. We demonstrate high performance and striking specificity with near-field absorption images of (sub)micron-sized islands of Low-Density Poly-Ethylene (LDPE) in a Poly-Styrene (PS) 50nm thin film. nano-FTIR spectra obtained on different sample regions clearly reveal the material-specific IR spectroscopic signatures of the respective polymers. The exceptional signal to noise ratio obtained for polymeric and even biological samples provides the basis to reduce measurement times by orders of magnitude and to acquire characteristic near-field spectra on the 100-200ms time scale. This allows hyperspectral imaging by recording a full FTIR-spectrum in each pixel of a scanned image with reasonable measurement durations. It enables for instance the elucidation of clustering and localized chemical interactions of polymers in a three-component polymer blend. Besides non-invasive nanoscale resolved material identification, nano-FITR permits quantitative measurements of dielectric values for polymers or the determination of free carrier concentration and mobility in low-dimensional structures.

nano-FTIR: Near-field spectroscopy of polymers at sub200ms per spectrum speed and sub20nm spatial resolution

255th National Meeting (2018)

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