Precursors And Surface Activation In The Synthesis Of Ⅲ-Ⅴ Quantum Dots

Semiconductor nanocrystals with sizes in the quantum-confinement regime(quantum dots,QDs)have gained tremendous attention in the past decades,because of its excellent optical and optoelectronic properties.The current workhorse of QDs is the system based on cadmium chalcohenide and other Ⅱ-Ⅵ QDs.The potential toxicity of cadmium bears health and environmental concerns.Ⅲ-Ⅴ QDs may be the best candidates of non-cadmium QDs,which could offer compatible properties withⅡ-Ⅵ QDs but without intrinsic toxicity since Ⅲ-Ⅴ QDs have no Class A elements(Cd,Pb and Hg).The far lag behind synthetic chemistry results in the retarded development of Ⅲ-Ⅴ QDs.This thesis aims primarily to explore the fundamental factors related to synthetic development of Ⅲ-Ⅴ QDs,understand the reaction mechanism in growth stage,and put forward new methods to synthesize high qualityⅢ-Ⅴ QDs.Precursors and QDs themselves are two main parts in the synthetic chemistry of III-V QDs.Recent studies have proven that changing the reactivity of anionic precursor led to less improvement of Ⅲ-Ⅴ QDs,so we first focused on the possibility of activating the cationic precursor.Instead of fatty amine mentioned by references,alkyl phosphines could activate indium carboxylate efficiently at room temperature,and change the way of nucleation in the synthesis of Ⅲ-Ⅴ QDs.As a result,the quality of Ⅲ-Ⅴ QDs could be much improved.By systematic studies on growth of InP QDs,dense and tight ligand passivation on QDs surface was identified as the key barrier to efficient growth of nanocrystals.Self-nucleation would be unavoidable once active monomers(precursors)could not be used for efficient growth.For seeded-growth,this would induce the entanglement of nucleation and growth of the nanocrystals.To solve this problem,surface activation was proposed.Specificlly,with commonly applied indium and phosphorous█precursors,surface ligands can become dynamic through surface activation and allow full growth of the QDs without nucleation.Surface activation was proven to effectively break the growth bottleneck of InP QDs.Two types of surface activation reagents were tested.The first type shortened the chain length of the alknoate ligands,which should reduce diffusion barrier from the bulk solution to the surface of existing QDs.The second type possessed a larger footprint than the common ligands,so that monomers could better penetrate the ligand shell on surface of the QDs.Both strategies worked well.2,4-diketones were identified as the most efficient activation reagents,which rendered full growth of the InP QDs without self-nucleation at mild temperatures(140-180℃).With acetyacetone as surface activation reagents,a series of size-tunable InP QDs with good size distribution were obtained and the growth bottleneck were broken readily.Furthermore,surface activation was generally applicable for InAs and other III-V based core/shell QDs,including InP/ZnSe,InP/GaP,InAs/InP ones.Surface activation enabled us to synthesize III-V QDs with a more convenient,efficient and energy saving method.Results presented in this thesis should promote fundamental research and technical applications of III-V QDs as cadmium-free QD emitters.