Atomic and Electronic Structure of Epitaxial Necking in Quantum Dot Super Lattice

Quantum coupling between periodic nanocrystalline structures manifests novel mesoscale properties such as mini-band formation, which may induce high carrier mobility¹. Colloidal PbSe quantum dots (QDs) can self-assemble into 3D superlattices and are a promising material system to realize these synergistic properties. In this work, the electronic structures of these systems are investigated with advanced metrology and the modulation of electronic band structure in QD epi-SL by the formation of epitaxial neck between the QDs were observed. Experiments revealed unexpectedly large zero conductance (band) gap formation (~1.1 eV) when the STS probe was located between the QDs, while a smaller band gap of ~0.7 eV was observed when probing the body of the QD, as expected. Monochromated STEM-EELS were performed on the monolayer epi-SL and the band gap modification as a function of the electron probe position studied which shown a high onset for the energy loss when the electron probe was positioned on the QD neck, while a smaller onset was observed when the probe was directly on the QD. It is hypothesized that the epitaxial necks between the QDs confines the electron (hole) wave functions, thereby forming large band gaps on the epitaxial necking regions.