2 research outputs found
Quantitative Measurement of Local Infrared Absorption and Dielectric Function with Tip-Enhanced Near-Field Microscopy
Scattering-type
scanning near-field optical microscopy (s-SNOM)
and Fourier transform infrared nanospectroscopy (nano-FTIR) are emerging
tools for nanoscale chemical material identification. Here, we push
s-SNOM and nano-FTIR one important step further by enabling them to
quantitatively measure local dielectric constants and infrared absorption.
Our technique is based on an analytical model, which allows for a
simple inversion of the near-field scattering problem. It yields the
dielectric permittivity and absorption of samples with 2 orders of
magnitude improved spatial resolution compared to far-field measurements
and is applicable to a large class of samples including polymers and
biological matter. We verify the capabilities by determining the local
dielectric permittivity of a PMMA film from nano-FTIR measurements,
which is in excellent agreement with far-field ellipsometric data.
We further obtain local infrared absorption spectra with unprecedented
accuracy in peak position and shape, which is the key to quantitative
chemometrics on the nanometer scale
Nano-FTIR Absorption Spectroscopy of Molecular Fingerprints at 20Â nm Spatial Resolution
We demonstrate Fourier transform infrared nanospectroscopy
(nano-FTIR)
based on a scattering-type scanning near-field optical microscope
(s-SNOM) equipped with a coherent-continuum infrared light source.
We show that the method can straightforwardly determine the infrared
absorption spectrum of organic samples with a spatial resolution of
20 nm, corresponding to a probed volume as small as 10 zeptoliter
(10<sup>–20</sup> L). Corroborated by theory, the nano-FTIR
absorption spectra correlate well with conventional FTIR absorption
spectra, as experimentally demonstrated with polyÂ(methyl methacrylate)
(PMMA) samples. Nano-FTIR can thus make use of standard infrared databases
of molecular vibrations to identify organic materials in ultrasmall
quantities and at ultrahigh spatial resolution. As an application
example we demonstrate the identification of a nanoscale PDMS contamination
on a PMMA sample