Semiconductor nanoparticles on solid substrates: Film structure, intermolecular interactions, and polyelectrolyte effects

Citrate-stabilized CdSe or CdSe/CdS core-shell nanoparticles (NPs) were adsorbed on the standard silicon wafers bearing either a short-chain covalently bound adsorption promoter (3-aminopropyl)-triethoxylsilane (APTES) or macromolecular adsorption promoters-polyethylenimine (PEI) or poly(diallydimethylammonium) chloride (PDDA). The aim of this study is 2-fold: (1) to compare different methods of NP processing into thin films and (2) to elucidate the effect of the long-chain dynamics on the NP film structure. Systematic atomic force microscopy study of the films revealed that both types of NPs produced densely packed films on PDDA, while rarified films with significant clustering formed on PEI and APTES. The difference in NP layer morphologies was rationalized on the basis of intermolecular NP-polyelectrolyte interactions. Importantly, we observed that the adsorption layer of the weak polyelectrolyte PEI could alter its chain distribution by partial wrapping around the NPs, while no disturbance in APTES and PDDA monolayer by NP was observed. This was attributed to more labile binding of PEI to the solid substrate than for other adsorption promoters.