  The expanding application spectrum of plasmonic nanoantennas demand versatile
design approaches to tailor the antenna properties for specific requirements.
The design efforts primarily concentrate on shifting the operation wavelength
or enhancing the local fields by manipulating the size and shape of the
nanoantenna. Here, we propose a design path to control the absorption and
scattering characteristics of a dipole nanoantenna by introducing a hollow
region inside the nanostructure. The resulting contour geometry can
significantly suppress the scattering of the dipole nanoantenna and enhance its
absorption simultaneously. Both the dipole and the contour dipole nanoantenna
couple to equivalent amount of the incident radiation. The dipole nanoantenna
scatters 84% of the coupled power (absorbs the remaining 16%) whereas the
contour dipole structure scatters only 28% of the coupled power (absorbs the
remaining 72%). This constitutes the transformation from scatter to absorber
nanoantenna. The scattering of a contour nanoantenna can be further suppressed
by incorporating a lossless dielectric in the hollow region without altering
its absorption. We also demonstrate the applicability of scattering suppression
and absorption enhancement features of the contour design in other nanoantenna
geometries such as the self-assembly compatible nanoantenna structures of
nanodisk and nanoring chains. The benefits of the contour design can be readily
utilized in diverse applications; including bioplasmonics, medical
diagnosis/therapy, cloaked sensing, photovoltaics and thermoplasmonics.
