  Metal nanoantennas supporting localized surface plasmon resonances have
become an indispensable tool in bio(chemical) sensing and nanoscale imaging
applications. The high plasmon-enhanced electric field intensity in the visible
or near-IR range that enables the above applications may also cause local
heating of nanoantennas. We present a design of hybrid optical-thermal antennas
that simultaneously enable intensity enhancement at the operating wavelength in
the visible and nanoscale local temperature control. We demonstrate a
possibility to reduce the hybrid antenna operating temperature via enhanced
infrared thermal emission. We predict via rigorous numerical modeling that
hybrid optical-thermal antennas that support high-quality-factor
photonic-plasmonic modes enable up to two orders of magnitude enhancement of
localized electric fields and of the optical power absorbed in the nanoscale
metal volume. At the same time, the hybrid antenna temperature can be lowered
by several hundred degrees with respect to its all-metal counterpart under
continuous irradiance of 104-105 W/m2. The temperature reduction effect is
attributed to the enhanced radiative cooling, which is mediated by the
thermally-excited localized surface phonon polariton modes. We further show
that temperature reduction under even higher irradiances can be achieved by a
combination of enhanced radiative and convective cooling in hybrid antennas.
Finally, we demonstrate how hybrid optical-thermal antennas can be used to
achieve strong localized heating of nanoparticles while keeping the rest of the
optical chip at low temperature.
