Investigation of CdS/Se Surfaces: How Dipole Interaction and Impurities Influence the Growth Process

Nanoparticles can spontaneously assemble into larger, microscale structures due to direct specific interactions and/or indirectly through the environment. Experimentally we synthesized core/shell CdS/Se structure tetrahedral building blocks which led to bernal spine structure, hexagonal wire and fcc/bcc superlattices. In order to understand the self-assembly mechanism, we conducted several theoretical simulations. Using ab-initio first principles calculations, we predicted the surface orientations of tetrahedral building blocks by calculating surface energies, magnetic ordering and dipole moments. In order to replicate the experimental environment in our simulations, we passivated the dangling bonds of tetrahedral building blocks with different materials at various concentrations. (single-H, multiple-H, water molecules, acetic acid and phosphonic acid) For each type and concentration of passivation, we determined the binding mechanism and the effects on the dipole moment. Sequentially by training our monte carlo code (which takes into account the dipole interaction and energetics of passivation) with ab-initio calculations, we manage to predict the conditions for formation of different self-assembly geometries and verified our experimental results.