Microfabrication of freestanding porous silicon particles containing spectral barcodes

A method to microfabricate micron-scale freestanding porous silicon photonic crystal particles is described. An electrochemically prepared film of porous silicon on a crystalline silicon substrate is patterned with an SU8-25 photoresist, and the unmasked porous silicon is removed with a chlorine plasma reactive ion etch. Porous microparticles are then removed from the substrate by electropolishing. Scanning electron microscopy and microscopic reflection spectroscopy are used to characterize the geometry and optical properties of the freestanding particles.