  We report on the structural and optical properties of individual bowtie
nanoantennas both on glass and semiconducting GaAs substrates. The antennas on
glass (GaAs) are shown to be of excellent quality and high uniformity reflected
by narrow size distributions with standard deviations for the triangle and gap
size of $\sigma_s^{glass}=4.5nm$ ($\sigma_s^{GaAs}=2.6nm$) and
$\sigma_g^{glass}=5.4nm$ ($\sigma_g^{GaAs}=3.8nm$), respectively. The
corresponding optical properties of individual nanoantennas studied by
differential reflection spectroscopy show a strong reduction of the localised
surface plasmon polariton resonance linewidth from $0.21eV$ to $0.07eV$ upon
reducing the antenna size from $150nm$ to $100nm$. This is attributed to the
absence of inhomogeneous broadening as compared to optical measurements on
nanoantenna ensembles. The inter-particle coupling of an individual bowtie
nanoantenna, which gives rise to strongly localised and enhanced
electromagnetic hotspots, is demonstrated using polarization-resolved
spectroscopy, yielding a large degree of linear polarization of
$\rho_{max}\sim80\%$. The combination of highly reproducible nanofabrication
and fast, non-destructive and non-contaminating optical spectroscopy paves the
route towards future semiconductor-based nano-plasmonic circuits, consisting of
multiple photonic and plasmonic entities.
