Scientists at the University of Delaware in Newark, Carnegie Mellon University in Pittsburgh and North Carolina State University in Raleigh have assembled one- and two-dimensional photonic crystals by exposing microspheres to an alternating electric field, which allows them to turn the particle ordering on and off. They suggest that the process, which they describe in the Feb. 10 issue of Applied Physics Letters, may enable the fabrication of switchable photonic materials, as well as solid materials, by embedding the arrays in solids by photopolymerization or sol-gel techniques.

In the work, they exposed 0.7- to 1.4-µm-diameter latex or silica particles to a 40- to 100-V alternating square-wave electric field in a 100-µm-thick cell comprising a glass slide, coverslip and silicon spacers. They analyzed the structure of the photonic crystals by monitoring the diffraction pattern of a transmitted HeNe laser beam through the sample and by observing the particles using optical microscopy.