Influence of Thermal Separation of Oleic Acid on the Properties of Quantum Dots Solutions and Optoelectronic of Their Langmuir Monolayers

Abstract

This article presents a description of a method of oleic acid separation from quantum dot (QD) solution. The oleic acid is a good stabilizer for CdSe/CdS/ZnS QD solution. QDs are an interesting material for fabricating the optoelectronic devices. The main disadvantage in QDs’ presence is an excess unbounded surfactant of the oleic acid. Oleic acid ligands have some defect on the morphology and modify the electronic structure of thin film QDs. One of the methods that allow to remove this excess surfactant is a separation by using high-density polyethylene (HDPE) membrane with thermal treatment. The thermal treatment has an effect on the separation of surfactants and the period of process. The changing in the number of surfactants in QD solution during various conditions is recorded by Langmuir-Blodgett (LB) technique. The QD monolayers are deposited on solid substrate by using Langmuir-Schaefer method. The changing in morphology is studied by atomic force microscopy (AFM). Photoluminescence (PL) spectra and photoconductivity properties of QDs are studied. The change in the surface pressure during separation was recorded. The conductivity enhancement and shifting of PL spectra were observed. It is related to decreasing number of an excess surfactant and changing structure of QDs’ outer shell.