Ag nanocrystals: 1. Effect of ligands on plasmonic properties

Silver nanocrystals (NCs) stabilized using amine-terminated coating agents (oleylamine or dodecylamine), their size ranging between 2 and 12 nm in diameter, are synthesized by hot injection methods. Their dispersion in size is relatively low (typically below 10%) without the need for a postsynthesis size segregation process. The amine-terminated coating agents are replaced by thiol-terminated molecules (dodecanethiol or hexadecanethiol) by ligand exchange, allowing the formation of alkanethiol coated Ag colloids. All NCs with various surface coatings are dispersed in toluene. Regardless of the nature of the coating agent, the surface plasmon resonance (SPR) is red-shifted with decreasing the NC size. For a given size, the SPR peak of thiol-stabilized NCs is shifted to lower energies compared to that of amine-stabilized NCs. Furthermore, with thiol-stabilized Ag NCs, the position of the SPR peak was found to be sensitive to the length of the alkyl chains of the coating agent, whereas minor differences are detected for Ag NCs coated with amines terminated with differing alkyl chain lengths.