BUNDLING AND INTERDIGITATION OF ADSORBED THIOLATE GROUPS IN SELF-ASSEMBLED NANOCRYSTAL SUPERLATTICES

Self-assembling of nanocrystals involves organization of nanocrystals encapsulated by protective compact organic molecules into a crystallin e material. The adsorbed molecules not only serve as the protection la yer for the nanocrystals but also provide the dominant cohesive intera ctions (or ''bonding'') sustaining the nanocrystal superlattices. The length of the adsorbed molecules is a controllable parameter, making t he ratio of particle size to interparticle distance an adjustable para meter that sensitively tunes the interparticle interaction/coupling an d resulting collective properties. In this paper, bundling and interdi gitation of thiolate molecules adsorbed on Ag nanocrystals are observe d using the chemical imaging technique in energy-filtered transmission electron microscopy (EF-TEM) at a resolution of similar to 2 nm. In t hese orientationally ordered, self-assembled Ag-nanocrystal superlatti ces, the bundling of the adsorbed molecules on the nanocrystal surface s is the fundamental structural principle. A model consistent with the nanocrystal's morphology and the interdigitation of the adsorbed thio lates is proposed.