Techniques for measuring the topography of a surface using a device including a semiconductor slab having a distal end and a base region, and an air slot therein. A sensor tip can be coupled to the slab below the air-slot. A photonic crystal including a lattice pattern with a cavity region defined by a local perturbation in the lattice pattern can be integrated into the semiconductor slab above and below the air slot, thereby providing a split-cavity photonic crystal resonator integrated into the semiconductor slab.