ELIXIR2

Project Objectives

The electronic and optical properties of semiconductor nanostructures are highly dependent on their size, shape and composition, which are thus essential to control. Colloidal synthesis enable the engineering of nanostructures with such precision and over a wide range of tunability. These structural features can be typically characterized by transmission electronic microscopy. However, controlling and characterizing the surface quality (passivation of dangling bounds), interface hetero-epitaxy (versus interfacial defects) and strain effects is much more challenging. Often, these properties are probed indirectly through measurements such as PL quantum yield and exciton lifetime. Ultrafast optical spectroscopy is an ideal tool to investigate exciton recombination, charge transfer and trapping dynamics in colloidal nanostructures, either dispersed in organic solvents, or embedded within solid-state matrices that are typically needed in opto-electronic devices. Furthermore, it can be used to study specific collective effects arising from inter-exciton or inter-particle interactions. Importantly, all these photo-physical properties can be used as a feedback loop to iteratively guide the chemical synthesis and design of specifically engineered hetero-nanostructures and assemblies. Specifically, these are two specific questions we aim to address by combining our interdisciplinary expertise: 1) How can we engineer CT excitons within out-of-plane heterostructures, which formation is typically prevented by the long, insulating surface ligands? For this, we need to master ligand exchange while preserving good surface passivation, quantum confinement and stable crystalline structures. 2) How can we obtain samples with all NPLs having a specific orientation (for Stark spectroscopy)? We will work on the protocol of NPL deposition on substrate or on the mechanical properties of the polymer used as matrix. Fluorescence anisotropy will be used to characterize the NPL orientation.