"Smart dust": nanostructured devices in a grain of sand.

The term "smart dust" originally referred to miniature wireless semiconductor devices made using fabrication techniques derived from the microelectronics industry. These devices incorporate sensing, computing and communications in a centimetre-sized package. This article discusses the construction of much smaller silicon-based systems, using the tools of nanotechnology. The synthesis of millimetre- to micron-sized functional photonic crystals made from porous silicon is described. It is shown how the various optical, chemical, and mechanical properties can be harnessed to perform sensing, signal processing, communication and motive functions.