Light-Controlled Electrostatic Self-Assembly of Quantum Dots

Abstract

Electrostatic self-assembly is one of the important self-assembly mechanisms that found use in optoelectronics. Although this method enables realizing unconventional architectures, producing complicated architectures in large areas requires local control over the self-assembly process. One of the ways to achieve this control is to provide enough kinetic energy to the self-assembling nanoparticles so that they can escape electrostatic attraction. We hypothesize that this energy can be delivered to the nanoparticles by treating them with light that can be absorbed by the particles. Here, we test this idea to tailor the electrostatic self-assembly of semiconductor quantum dots (QDs) using a laser. Employing fluorescence and atomic force microscopy, we demonstrate that the QDs are not attached to the substrate in regions where they are exposed to light while they are coated in the absence of optical excitation. We further conduct theoretical analysis to show that elevated temperatures indeed allow the QDs to escape the electrostatic attraction of the charged polymers on the surface. We also demonstrate that increasing the temperature during the coating process without irradiating the sample gives similar results as the case when the sample was irradiated. Finally, we fabricate an uncoated region on the self-assembled QD film with dimensions of similar to 200 mu m x 0.5 cm to demonstrate the feasibility of our approach to control the bottom-up self-assembly. We believe that our results may pave the way for a cost-effective and sustainable approach for the fabrication of nanoelectronic and optoelectronic devices.