CdS Nanocrystals

Semiconducting nanocrystals are of scientific interest in a variety of technical fields in the ability to tune them absorb or emit electromagnetic radiation at a desired wavelength not only by changing their composition but, more importantly, by changing their size. In medical physics one of their uses is as a biological marker, which works for much longer time than traditional chemical markers. Several separate markers can be placed in the body with very little, if any, interaction between the markers, and finally ligands can be attached to the surface that are tailored to attach to a specific protein. Computer modeling of the interaction of a ligand covered nanocrystal and the protein will improve our understanding of the effectiveness of identifying the protein through this process. As with experiments, understanding results of the computer modeling can be quite challenging; thus, we start with smaller less complicated systems and once we understand them we move on to progressively more complicated systems until we understand the system of interest.

Modeling spherical CdS nanocrystals with radii up to ~ 13nm, we have found that the reconstruction process has broken the point symmetries of the crystal in its zinc-blended structure, partially passivated the surface of the nanocrystal (decreasing the number of gap states), and that the molecular orbitals associated with the unpassivated bonds reside not only within the band gap of the nanocrystal, but also within the valence and conduction bands, decreasing the band gap.

Work on CdS-ZnS core-shell quantum dots is ongoing; with plans to begin work on semiconductor-ligand core shell nanocrystals shortly.