CdSe and CdSe(ZnS) quantum dots in 2D: A Langmuir monolayer approach

• CdSe and CdSe(ZnS) quantum dots were studied using the Langmuir monolayer technique.
• Surface chemistry revealed local-hexagonal packing at the air–water interface.
• Microscopy investigation showed a narrow size distribution of quantum dots.
• Films were analyzed to show thickness of layers as they formed at the interface.
• Self-assembly and interparticle distance was studied to determine optical properties.

Recent years have produced many advances in quantum dot synthesis, application and analysis while their importance in the fields of chemistry, biology, engineering and physics has grown as well. Opposed to the bulk state properties, quantum dots are dependent upon the quantum confinement effect in all three spatial dimensions and so their applications have been broadened to optical switches and fluorescence labeling among others. Compiled here are extensive results in the characterization of quantum dots using the Langmuir monolayer technique to approach these quantum dots in their two dimensional state. Variation of ligands around the nanoparticles at the air–water interface has revealed that a more condensed packing state is achieved with the use of smaller ligands. Properties such as the limiting nanoparticle area, molar absorptivity, and self-assembly manipulation have shown the local-hexagonal packing structure of the quantum dots at the air–water interface. As characterized by an expansion on the Langmuir technique, film thickness has also been analyzed under AFM and HR-TEM to observe the multilayer effect during isotherm formation.