ONLINE - Observation of phonon polaritons in multilayer hexagonal boron nitride films grown by chemical vapor deposition
CIC nanoGUNE Seminars
- Speaker
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Eugenio Calandrini, Nanooptics Group
- When
-
2022/02/21
12:00 - Place
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**Observation of phonon polaritons in multilayer hexagonal boron nitride films
grown by chemical vapor deposition **
Calandrini Eugenio
Nanooptics, CIC nanoGUNE
Hexagonal boron nitride (hBN) is a heavily studied van der Waals (vdW)
material that is able to support highly confined phonon polaritons (PhP) in
the mid-infrared spectral range. It inspired novel concepts in the field of
nanoscale infrared imaging, field-enhanced infrared sensing and vibrational
strong coupling. However, the typical approach for fabricating h-BN PhP
devices relies on mechanical exfoliation of bulk crystals, viable only for
proof-of-concept experiments due to its low yield. Although the interest in
producing hBN and other vdW materials by other means is raising, PhPs on
synthetized hBN were only reported on mono- and bilayers. PhP nanoresonators
and other devices based on such thin layers, however, may be unpractical for
real-world applications due to very small extinction cross sections.
Here we present a combined scattering-type scanning near-field optical
microscopy (s-SNOM) and far-field infrared spectroscopy study of wafer-scale
hBN films of several nanometer thickness, which were grown by chemical vapor
deposition (CVD) and transferred onto a Si/SiO2 substrate.
We performed far-field reflection spectroscopy in order to extract the
dielectric permittivity of the CVD grown hBN films and calculated the expected
dispersion and lifetime of the PhPs. Interestingly, and in stark contrast to
exfoliated hBN, s-SNOM imaging of the CVD grown material revealed random
interference patterns all over the film that we can attribute to PhP
scattering at randomly distributed defects in the hBN layer. To analyze these
patterns and determine the polariton dispersion and lifetime, we developed a
theoretical model and an experimental method. Finally, we designed and etched
hBN nanoribbons that exhibit transverse PhP resonances with quality factors
~50, which are only a factor of about two smaller than that of PhP resoantors
made of exfoliated hBN flakes . Our study shows the potential of CVD-grown hBN
layers to be used for large-scale fabrication of PhP based resonators and
devices, e.g. for infrared sensing applications.
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ONLINE nanoGUNE: Eugenio Calandrini, Nanooptics Group \- CIC nanoGUNE
When: Feb 21, 2022 11:00 AM
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