Silicon Nanocrystals: It's Simply a Matter of Size

Composed of one of the most earth abundant, low cost and least toxic elements, silicon nanocrystals exhibit quantum and spatial confinement effects when their size is diminished to that of the exciton, around 5 nm. With the recent discovery of various means for synthesizing and separating silicon nanocrystals into narrow size distribution mono-dispersions, it became possible for the first time to implement more deeply analytical studies of their size-dependent chemical, physical and biological properties than was possible with poly-dispersions. In this article we take a look at some recent studies of mono-dispersions of silicon nanocrystals where it is apparent that size really matters. With this newfound knowledge we imagine the new directions that the field may take in the future. The topics covered include how silicon nanocrystal size is manifest on their (i) surface structure and reactivity, (ii) optical and electronic properties, (iii) chemical and photochemical stability, and (iv) biochemical and cytotoxicity behavior. The article concludes with a vision of what the future might hold for this important class of nanocrystals.