  Si3N4 is an excellent material for applications of nanophotonics at visible
wavelengths due to its wide bandgap and moderately large refractive index (n
$\approx$ 2.0). We present the fabrication and characterization of Si3N4
photonic crystal nanobeam cavities for coupling to diamond nanocrystals and
Nitrogen-Vacancy centers in a cavity QED system. Confocal
micro-photoluminescence analysis of the nanobeam cavities demonstrates quality
factors up to Q ~ 55,000, which is limited by the resolution of our
spectrometer. We also demonstrate coarse tuning of cavity resonances across the
600-700nm range by lithographically scaling the size of fabricated devices.
This is an order of magnitude improvement over previous SiNx cavities at this
important wavelength range.
