6 research outputs found
Supplementary document for Nano-compositional imaging of the lanthanum silicide system at THz wavelengths - 6651359.pdf
Supplementar
Ultrafast Dynamics of Surface Plasmons in InAs by Time-Resolved Infrared Nanospectroscopy
We report on time-resolved mid-infrared
(mid-IR) near-field spectroscopy
of the narrow bandgap semiconductor InAs. The dominant effect we observed
pertains to the dynamics of photoexcited carriers and associated surface
plasmons. A novel combination of pump–probe techniques and
near-field nanospectroscopy accesses high momentum plasmons and demonstrates
efficient, subpicosecond photomodulation of the surface plasmon dispersion
with subsequent tens of picoseconds decay under ambient conditions.
The photoinduced change of the probe intensity due to plasmons in
InAs is found to exceed that of other mid-IR or near-IR media by 1–2
orders of magnitude. Remarkably, the required control pulse fluence
is as low as 60 μJ/cm<sup>2</sup>, much smaller than fluences
of ∼1–10 mJ/cm<sup>2</sup> previously utilized in ultrafast
control of near-IR plasmonics. These low excitation densities are
easily attained with a standard 1.56 μm fiber laser. Thus, InAsa
common semiconductor with favorable plasmonic properties such as a
low effective massî—¸has the potential to become an important
building block of optically controlled plasmonic devices operating
at infrared frequencies
Recommended from our members
Tuning and Persistent Switching of Graphene Plasmons on a Ferroelectric Substrate
We characterized plasmon propagation
in graphene on thin films of the high-κ dielectric PbZr<sub>0.3</sub>Ti<sub>0.7</sub>O<sub>3</sub> (PZT). Significant modulation
(up to ±75%) of the plasmon wavelength was achieved with application
of ultrasmall voltages (< ±1 V) across PZT. Analysis of the
observed plasmonic fringes at the graphene edge indicates that carriers
in graphene on PZT behave as noninteracting Dirac Fermions approximated
by a semiclassical Drude response, which may be attributed to strong
dielectric screening at the graphene/PZT interface. Additionally,
significant plasmon scattering occurs at the grain boundaries of PZT
from topographic and/or polarization induced graphene conductivity
variation in the interior of graphene, reducing the overall plasmon
propagation length. Lastly, through application of 2 V across PZT,
we demonstrate the capability to persistently modify the plasmonic
response of graphene through transient voltage application
Terahertz Nanoimaging of Graphene
Accessing the nonradiative near-field
electromagnetic interactions with high in-plane momentum (<i>q</i>) is the key to achieve super resolution imaging far beyond
the diffraction limit. At far-infrared and terahertz (THz) wavelengths
(e.g., 300 μm = 1 terahertz = 4 meV), the study of high <i>q</i> response and nanoscale near-field imaging is still a nascent
research field. In this work, we report on THz nanoimaging of exfoliated
single and multilayer graphene flakes by using a state-of-the-art
scattering-type near-field optical microscope (s-SNOM). We experimentally
demonstrated that the single layer graphene is close to a perfect
near-field reflector at ambient environment, comparable to that of
the noble metal films at the same frequency range. Further modeling
and analysis considering the nonlocal graphene conductivity indicate
that the high near-field reflectivity of graphene is a rather universal
behavior: graphene operates as a perfect high-<i>q</i> reflector
at room temperature. Our work uncovers the unique high-<i>q</i> THz response of graphene, which is essential for future applications
of graphene in nano-optics or tip-enhanced technologies
Efficiency of Launching Highly Confined Polaritons by Infrared Light Incident on a Hyperbolic Material
We
investigated phonon–polaritons in hexagonal boron nitridea
naturally hyperbolic van der Waals materialî—¸by means of the
scattering-type scanning near-field optical microscopy. Real-space
nanoimages we have obtained detail how the polaritons are launched
when the light incident on a thin hexagonal boron nitride slab is
scattered by various intrinsic and extrinsic inhomogeneities, including
sample edges, metallic nanodisks deposited on its top surface, random
defects, and surface impurities. The scanned tip of the near-field
microscope is itself a polariton launcher whose efficiency proves
to be superior to all the other types of polariton launchers we studied.
Our work may inform future development of polaritonic nanodevices
as well as fundamental studies of collective modes in van der Waals
materials
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