The electrical excitation of guided
plasmonic modes at the nanoscale
enables integration of optical nanocircuitry into nanoelectronics.
In this context, exciting plasmons with a distinct modal field profile
constitutes a key advantage over conventional single-mode integrated
photonics. Here, we demonstrate the selective electrical excitation
of the lowest-order symmetric and antisymmetric plasmonic modes in
a two-wire transmission line. We achieve mode selectivity by precisely
positioning nanoscale excitation sources, i.e., junctions for inelastic
electron tunneling, within the respective modal field distribution.
By using advanced fabrication that combines focused He-ion beam milling
and dielectrophoresis, we control the location of tunnel junctions
with sub-10 nm accuracy. At the far end of the two-wire transmission
line, the guided plasmonic modes are converted into far-field radiation
at separate spatial positions showing two distinct orthogonal polarizations.
Hence, the resulting device represents the smallest electrically driven
light source with directly switchable polarization states with possible
applications in display technology.
We recorded diffraction patterns using a commercially available slit and sensor over a wide range of experimental circumstances, including near- and far-field regimes and oblique incidence at large angles. We then compared the measured patterns with theoretical intensity curves calculated via the numerical integration of formulas derived within the framework of scalar diffraction theory. Experiment and theory show particularly good agreement when the first Rayleigh–Sommerfeld (R-S) formula is used. The Kirchhoff formula, though problematic in the context of mathematical consistency, agrees with the first R-S formula, even for large incidence angles, whereas the second R-S formula differs visibly. To obtain such a good agreement, we replaced the assumption of an incident plane wave with that of a Gaussian beam and implemented geometric corrections to account for slit imperfections. These results reveal how the scope of scalar diffraction theory can be extended with a small set of auxiliary assumptions.
Visible and infrared photons can be detected with a broadband
response
via the internal photoeffect. By use of plasmonic nanostructures,
i.e., nanoantennas, wavelength selectivity can be introduced to such
detectors through geometry-dependent resonances. Also, additional
functionality, like electronic responsivity switching and polarization
detection, has been realized. However, previous devices consisted
of large arrays of nanostructures to achieve detectable photocurrents.
Here we show that this concept can be scaled down to a single antenna
level, resulting in detector dimensions well below the resonance wavelength
of the device. Our design consists of a single electrically connected
plasmonic nanoantenna covered with a wide-bandgap semiconductor allowing
broadband photodetection in the visible/near-infrared via injection
of hot carriers. We demonstrate electrical switching of the color
sensitivity as well as polarization detection. Our results hold promise
for the realization of ultrasmall photodetectors with advanced functionality.
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