Characterization and 2D self-assembly of CdSe quantum dots at the air-water interface

Langmuir film properties, UV-vis spectroscopy, epifluorescence microscopy, and transmission electron microscopy were used to study CdSe quantum dots (QDs) in 2D. By combining these results, it was possible to determine the molar absorptivity, limiting nanoparticle area, luminescence property, and arrangement of the QDs in the monolayer films at the air-water interface. Either trioctylphosphine oxide (TOPO) or 1-octadecanethiol (ODT) stabilized the QDs. The data collected reveal that TOPO forms close-packed monolayers on the surface of the QDs and that ODT-stabilized QDs undergo alkyl chains interdigitation. It was also found that varying the nanoparticle size, nature of surfactant, surface pressure, and mixed monolayers could help engineer the 2D self-assembly of the QDs at the air-water interface. Of practical importance is the transfer of these monolayer films onto hydrophilic or hydrophobic solid substrates, which could be successfully accomplished via the Langmuir-Blodgett film deposition technique.