an order of magnitude greater than the $Q_o$ of the PCC designed following the standard deterministic recipe based on bandedge matching. This can be explained by this design’s lower mode frequency $a/\lambda=0.40$ that is further from the air light-line and as a result has less vertical radiation loss. For comparison, the trajectories of the hole mirror strengths of both the band-edge matching design (dotted line) and the highly elliptical to round hole fill-factor design (dashed line) are shown in Fig. \[figureTwo\](e). Also note the solid white equi-frequency line at the target frequency in this Figure. We expect that numerical optimization in future work, e.g. using a genetic algorithm [@goh2007genetic], would allow $Q_o$ to be increased further.

Creating split-beam and paddle nanocavity optomechanical devices
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We now show how the highly elliptical hole device from Fig. \[figureTwo\](d) can be used as the basis for the split-beam cavity shown in Fig. \[figureThree\](a). A split-beam cavity is formed by making a clear cut through the centre of the nanobeam, creating nanocantilevers whose mechanical modes are similar to those used in many sensing and metrology applications. Placing the cut in the centre of PCC ensures that the nanocantilever motion interacts strongly with the optical 