Photonic barcodes (a and e) produced by two different porous silicon microspheres. The location and width of the bars are determined by the position and FWHM of the resonances of their PL spectra (b and f, respectively). Optical microscopy images of the microspheres, taken at × 1,000 magnification in reflection (c and g) and in transmission (d and h) modes indicate, within the limited resolution of this technique, sphere diameter values of 4.1 and 3.7 μm, respectively (reprinted with the permission of ).
Ramiro-Manzano et al. Nanoscale Research Letters 2012 7:497 doi:10.1186/1556-276X-7-497