Growth of monodisperse quantum dots (QDs) is a pressing requirement in the context of commercial application as well as academic study, as the size uniformity is directly related to color purity in display products which have been commercialized. In the sense, understanding on the generation of active species via thermolysis of precursors, diffusion of precursors from bulk solution onto nanocrystal surface, and surface growth reaction kinetics has been ever more important. In this presentation, I will present our recent findings pertaining to these issues on the basis of different material examples.<br/><br/>We have investigated diffusion of active species monomers through ligand layers using CdSe nanorods (NRs) as a model system. I present a new answer for detailed growth mechanism of colloidal semiconductor NRs. For this, we developed dual-diameter nanorod (DDNR) structure via colloidal synthesis, where two sections along the long axis in each NR have different diameters at a few nanometer scale. The vivid segmentation is an ideal platform for monitoring the growth process of NRs, presenting important determinants in the reactivity of distinguishable NR facets. The lesson obtained from DDNR is universally applied to nanocrystal growth in any colloidal batch. By controlling the discovered factors, single-diameter NRs with controllable core position also became available. I will put the findings in perspective by outlining the effect of diffusion of monomers and surface growth reactions.<br/><br/>In addition, we have observed that density of surface ligands alters the colloidal interaction between nanorods, ultimately affecting the way NRs assemble during the film deposition process. Assembly of CdSe/CdS core/shell NRs results in various ordered structures in the presence of free oleic acid molecules. Electron microscopy and X-ray scattering data suggest that the assembly is initiated at the air-dispersion interface due to the preferential depletion attraction of NR sidewall to the interface. Interestingly, subsequent growth of superstructures depends heavily on the ligand density that determines the relative magnitude of interface-NR depletion attraction to inter-NR attraction. Highly ordered structures of NRs, especially for the monolayer smectic-phase, are promising as a polarizable emissive layer for optical devices. I will discuss the implication of the growth and assembly of nanorods in the context of design of high-efficiency light emitting devices based on QDs.

Colloidal ii-vi semiconductor nanorods: Growth and assembly controlled by surface ligands

2019 Spring National Meeting

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