Surface passivation effects on the electronic and optical properties of 3C-SiC nanocrystals

Using time-dependent density functional theory the optical absorption spectrum of SiC nanocrystals was studied with changes in their surface structures as they are passivated with some functional groups such as amine (–NH2), amide (–CONH2), hydroxyl (–OH), carboxylic acid (–CO2H) and thiol (–SH) groups. The variations of some quantities such as formation energy, optical gap, single particle energy gap and lowest exciton binding energy of SiC nanocrystals are discussed with changes in their surface structure. Results indicate that in all cases the silicon dangling bonds on the surface of SiC nanocrystals are favorable for constructing stable structures with attached functional groups as in some cases their stability is more than pure hydrogenated SiC nanocrystal as an ideal structure. Also the functional groups attached to the surface of SiC nanocrystals change the optical properties of the SiC nanocrystals as the changes are remarkable for amide and thiol passivated nanocrystals.