  We present the design, fabrication and initial characterization of a paddle
nanocavity consisting of a suspended sub-picogram nanomechanical resonator
optomechanically coupled to a photonic crystal nanocavity. The optical and
mechanical properties of the paddle nanocavity can be systematically designed
and optimized, and key characteristics including mechanical frequency easily
tailored. Measurements under ambient conditions of a silicon paddle nanocavity
demonstrate an optical mode with quality factor $Q_o$ ~ 6000 near 1550 nm, and
optomechanical coupling to several mechanical resonances with frequencies
$\omega_m/2\pi$ ~ 12-64 MHz, effective masses $m_\text{eff}$ ~ 350-650 fg, and
mechanical quality factors $Q_m$ ~ 44-327. Paddle nanocavities are promising
for optomechanical sensing and nonlinear optomechanics experiments.
