A Method to Form Molecular Nanorods Using Inorganic Nanoparticles As Nucleation Seeds

This paper describes a method to nucleate molecular crystalline nanorods from inorganic nanoparticles. The method is demonstrated using n-carboxylic acids that crystallize from organic solvents, such as ethanol and isopropanol, by solvent evaporation. Thiolate-protected inorganic nanoparticles including CdSe, CdS, and Au are used as nucleation seeds. n-Carboxylic acids form highly ordered 2-D crystalline layers on highly oriented pyrolytic graphite (HOPG). However, when crystallization occurs in the vicinity of the nanoparticles, the persistent HOPG-dominated nano-stripe pattern is disrupted, and nanorods attached to the nanoparticles become the dominant feature. In order to understand the underlying mechanism, the effects of film-forming conditions, carboxylic acid chain length, nanoparticle size, and chemical composition of the nanoparticle are examined. It is determined that high colloidal stability of the nanoparticles is a prerequisite for seed-mediated nucleation. A carboxylic chain length range amenable to the nanorod formation is identified, as is the relationship between the nanoparticle size and the number of nanorods per nanoparticle. This study contributes to solution-based bottom-up processes of nanocrystals that may be applicable to a variety of molecular crystalline compounds.