1 research outputs found
Nanoantenna-Enhanced Infrared Spectroscopic Chemical Imaging
Spectroscopic
infrared chemical imaging is ideally suited for label-free
and spatially resolved characterization of molecular species, but
often suffers from low infrared absorption cross sections. Here, we
overcome this limitation by utilizing confined electromagnetic near-fields
of resonantly excited plasmonic nanoantennas, which enhance the molecular
absorption by orders of magnitude. In the experiments, we evaporate
microstructured chemical patterns of C<sub>60</sub> and pentacene
with nanometer thickness on top of homogeneous arrays of tailored
nanoantennas. Broadband mid-infrared spectra containing plasmonic
and vibrational information were acquired with diffraction-limited
resolution using a two-dimensional focal plane array detector. Evaluating
the enhanced infrared absorption at the respective frequencies, spatially
resolved chemical images were obtained. In these chemical images,
the microstructured chemical patterns are only visible if nanoantennas
are used. This confirms the superior performance of our approach over
conventional spectroscopic infrared imaging. In addition to the improved
sensitivity, our technique provides chemical selectivity, which would
not be available with plasmonic imaging that is based on refractive
index sensing. To extend the accessible spectral bandwidth of nanoantenna-enhanced
spectroscopic imaging, we employed nanostructures with dual-band resonances,
providing broadband plasmonic enhancement and sensitivity. Our results
demonstrate the potential of nanoantenna-enhanced spectroscopic infrared
chemical imaging for spatially resolved characterization of organic
layers with thicknesses of several nanometers. This is of potential
interest for medical applications which are currently hampered by
state-of-art infrared techniques, e.g., for distinguishing cancerous
from healthy tissues