2 research outputs found
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
Ultrafast and Nanoscale Plasmonic Phenomena in Exfoliated Graphene Revealed by Infrared Pump–Probe Nanoscopy
Pump–probe spectroscopy is
central for exploring ultrafast
dynamics of fundamental excitations, collective modes, and energy
transfer processes. Typically carried out using conventional diffraction-limited
optics, pump–probe experiments inherently average over local
chemical, compositional, and electronic inhomogeneities. Here, we
circumvent this deficiency and introduce pump–probe infrared
spectroscopy with ∼20 nm spatial resolution, far below the
diffraction limit, which is accomplished using a scattering scanning
near-field optical microscope (s-SNOM). This technique allows us to
investigate exfoliated graphene single-layers on SiO<sub>2</sub> at
technologically significant mid-infrared (MIR) frequencies where the
local optical conductivity becomes experimentally accessible through
the excitation of surface plasmons via the s-SNOM tip. Optical pumping
at near-infrared (NIR) frequencies prompts distinct changes in the
plasmonic behavior on 200 fs time scales. The origin of the pump-induced,
enhanced plasmonic response is identified as an increase in the effective
electron temperature up to several thousand Kelvin, as deduced directly
from the Drude weight associated with the plasmonic resonances