Figure 5 .

Fabrication of 2D photonic slab with square lattice of air hole in a silicon matrix. (a) Proton beam-writing process and resultant 3D defect distribution. (b) Selective formation of porous silicon in circular regions in subsequent electrochemical etching in HF electrolyte. (c) SEM image of the freestanding photonic slab structure after removal of porous silicon.