Connected but Confined: Surface Functionalization of Semiconducting Nanocrystals

Connected but Confined: Surface Functionalization of Semiconducting Nanocrystals

Semiconductor colloidal nanocrystals (NCs) have attracted much attention in the past decade due to their unique size and shape dependent properties. In most of the successful synthetic routes to colloidal NCs, the use of bulky hydrocarbon (C₈-C₁₈) molecules with coordinating functional groups (such as -COOH, -NH₂, etc) as surfactant ligands is crucial for stabilization, as well as for size and shape control of NCs. The presence of these large organic molecules, however, creates highly insulating barriers which block the electronic communication between NCs, limiting the applications of assemblies of colloidal NCs. We have developed a novel chemical method to efficiently remove these surfactant ligands. This unique surface modification process produces bare nanocrystals without any surfactant ligands, which has been confirmed by FTIR and elemental analysis. GISAX study also reveals a significant decrease on inter-particle spacing. The bare nanocrystals are attached but maintain quantum confinement. Such "connected but confined" nanocrystal assemblies exhibit much stronger inter-particle coupling, and are promising new materials for fabricating electronic and optoelectronic devices.