Silicon in a new light

Cherenkov radiation can be used to study the optical properties of silicon nanocomposite materials

Credit: © 2008 APS

Silicon nanoparticles and related composites could play an important role in future silicon-based photonic devices. However, there is still only a limited understanding of their physical properties on the nanoscale. Now, analysis of the energy lost by electrons travelling at very high speeds through these materials shows potential for studying their optical properties with Angstrom spatial resolution.

Aycan Yurtsever and co-workers¹ from Cornell University sent a beam of 200-keV electrons through silicon nanoparticles embedded in SiO₂. Because these electrons travel through the nanoparticles faster than the speed of light in silicon, they produce Cherenkov radiation — the radiation that is responsible for the blue glow observed in nuclear reactors.

The Cornell team found weak but definite Cherenkov radiation and 'wave-guided modes' when silicon nanoparticles with diameters of 4.2 nm were separated by about 8 nm on average. These results imply that the particle size and spacing of these structures were much shorter than the Cherenkov wavelengths.