LEAD CHALCOGENIDE QUANTUM DOT ASSEMBLY AND ATTACHMENT ON FLUID INTERFACES

Abstract

The formation of tiles composed of quantum dots is thought to constitute a new class of self- assembled nanostructured material. Understanding the dynamic physicochemical processes that govern the assembly at a functionalized fluid interface is crucial. We aim to seek design guidance for future advances in improving the assembly result of nanostructured nanocrystals (NCs). What is expected is that a functionalized liquid interface potentially provides more control over the behavior of the nanocrystals (NCs), which increases the complexity of the assembly process. To investigate this self-assembly process, we investigate the insight from the fundamental molecular-level interactions, and we use Molecular Dynamics (MD) simulations to investigate the process. The model system studied here was composed of lead chalcogenide NCs, covered with lead oleate molecules (ligands), and assembled on a monolayer (ML) composed of amphiphile (DPPC) molecules. The impact of ML density and structure of amphiphile molecules are extracted as two main factors of interest. The simulations aimed to reveal the role of the nature of the monolayer interface on NCs assembly process. Before testing the impact of monolayer parameters on the self-assembly of the NCs, we used density functional theory to confirm that the energy barrier for ligand dissociation from the surface of the NC was high and, as such, are unlikely to detach readily. We studied the degree of NC in-plane orientation and out-of-plane tilt degree during the process as two means of evaluating the NCs’ alignment. We generated simulations focusing on the impact of these two factors on self- assembly that will bring us practical insights into how ML density and the chain length of ML molecules affect the self-assembly performance. We uncover a trend of the analytical attachment among various NCs assembly processes that reflects the contributions that ML density and length of alkyl chain made to the formation of defects in dimer alignments. The simulations and experiments presented in this study provide concrete design rules for the assembly of NCs for further research on superlattice formation.