Thermally degradable ligands for nanocrystals
Andrew W Wills1, Moon Sung Kang, Ankur Khare
1Department of Chemistry, University of Minnesota, 421 Washington Avenue SE, Minneapolis, Minnesota 55455-0132, USA.
ACS Nano
|August 25, 2010
Summary
Researchers developed a new method using octyldithiocarbamate ligands to remove insulating ligands from lead selenium/cadmium selenium (PbSe/CdSe) core/shell nanocrystals at lower temperatures. This enables efficient formation of conductive quantum-confined nanocrystal films.
Area of Science:
- Materials Science
- Nanotechnology
- Solid State Physics
Background:
- Oleate ligands on lead selenium/cadmium selenium (PbSe/CdSe) core/shell nanocrystals hinder their conductivity.
- Removing these insulating ligands typically requires high temperatures (330°C), risking nanocrystal degradation and loss of quantum confinement.
- Developing efficient ligand removal methods is crucial for fabricating functional nanocrystal-based electronic devices.
Purpose of the Study:
- To investigate the exchange of oleate ligands with octyldithiocarbamate on PbSe/CdSe core/shell nanocrystals.
- To determine the effectiveness of gentle heating for removing octyldithiocarbamate ligands and enabling dense film formation.
- To assess the impact of this ligand removal process on the electrical conductivity and quantum confinement of the nanocrystals.
Main Methods:
- Ligand exchange from oleate to octyldithiocarbamate on PbSe/CdSe core/shell nanocrystals.
- Annealing treatments at temperatures ranging from 140°C to 205°C to remove octyldithiocarbamate ligands.
- X-ray diffraction (XRD) and transmission electron microscopy (TEM) for structural analysis.
- Measurement of electrical conductivity before and after annealing.
Main Results:
- Octyldithiocarbamate ligands were effectively removed at significantly lower temperatures (140-205°C) compared to oleate (330°C).
- Heating for 1 minute at 205°C removed 92% of organic ligands.
- Nanocrystal sintering, leading to loss of quantum confinement, occurred around 250°C.
- Densely packed films of quantum-confined nanocrystals were successfully prepared.
- Electrical conductivity increased by up to four orders of magnitude after annealing.
- The method was also applicable to Cadmium Selenide (CdSe) nanocrystals.
Conclusions:
- Octyldithiocarbamate serves as an effective ligand for low-temperature removal from PbSe/CdSe and CdSe nanocrystals.
- This facile ligand stripping enables the fabrication of highly conductive, quantum-confined nanocrystal films.
- The developed method offers a promising route for advancing nanocrystal-based electronic applications.
