external forces owing to a combination of low mechanical frequency $\omega_m$, effective mass $m_{eff}$, and spring-constant [@reinhardt2016ultralow]. For example, zipper cavities consisting of pairs of side-coupled dielectric-mode Si$_{3}$N$_{4}$ PCC’s [@Chan:09] have been fabricated with high aspect ratio tethers (115 $\mu$m x 130 nm) for ultrasensitive accelerometers [@Krause:12] and studying feedback cooling [@Krause:15]. As well, Si$_{3}$N$_{4}$ is compatible with standard silicon and CMOS manufacturing processes, has low optical absorption from telecom through most visible wavelengths with nominally no two-photon absorption at telecommunication wavelengths, and can be integrated with lithium niobate [@chang2017heterogeneous]. However, its relatively low refractive index is detrimental to high-$Q_o$ air-mode PCC design [@Barth:08; @McCutcheon:08] due to its reduced optical energy confinement and resulting increased coupling to vertically radiating modes.

Air-mode PCC’s locally confine the higher energy conduction band mode of a photonic crystal waveguide through tapering a decreasing fill factor towards the centre of the crystal, and vice-versa for the dielectric mode. Encapsulated air-mode Si$_{3}$N$_{4}$ PCC’s with elliptical holes designed for 740-1000 nm wavelengths have been used to show the deterministic positioning of nanoparticles [@panettieri2016control; @fryett2018encapsulated; @chen2018deterministic]. However, most demonstrations of Si$_{3}$N$_{4}$ PCC’s to date have utilized the dielectric mode, ensuring that the bandedge frequency of the photonic crystal 