Nonlinear and linear properties of silicon nanoclusters

The nonlinear optical properties of small nano-scale semiconductors have been a topic of interest in recent years. Nano features in silicon have also been of great interest mainly because of their potential applications as active media for optical sources or storage media. Nano clusters of semiconductor materials embedded in a dielectric host material may be considered as a particular example of Conditional Artificial Dielectrics (CADs). These are composites whose dielectric properties can be activated by light. For example, the semiconductor clusters may be activated by photons having energy above the semiconductor bandgap to affect a propagating photon which possesses energy below the band-gap energy. Thus, the dielectric properties of such CADs can be controlled by external illumination. The absorption properties of CADs depend on the cluster size and conductivity. When the semiconductor particle size is reduced to the 2-3 nm range, low dimensional effects may be observed. Also, owing to the small size of the particles, bleaching of the absorption can be made very effectively and non-linear phenomenon can be seen at relatively low energy densities. In this paper, we describe, for the first time, the nonlinear optical behavior of silicon nanoclusters embedded on glass or quartz substrates by the use of laser ablation.