Doping of semiconductor nanocrystals by soft chemistry – NanoDoSe

The semiconductor nanocrystals exhibit exceptional optical properties; these can be modified through the incorporation of impurities in doping quantities.
The goal of this project is to develop new paths for the doping of nanocrystals by soft chemistry in order to ensure electronic and optical properties to nanocrystals. For example, few manganese atoms in zinc sulfide nanocrystals induce the apparition of a new transition in the visible range accompanied with magnetic properties. The introductions of cations with a valence different from the host material allow to electrically doped the nanocrystals through the introduction of holes or electrons.
Most of the syntheses of semiconductors nanocrystals are done at high temperature, temperatures beyond which the incorporation of impurities is especially difficult as they are often expel out of the particules, that’s why we will focus on the doping at room temperature in solution. Two different approaches will be explored:
- The introductions of dopants through a partial cation exchange with silver, copper or gold. These last couple of years, many progresses has been done in the domain and it is possible to fully exchange the cationic lattice of nanocrystals of different shapes. Thanks to a fine control of the partial ligand exchange, it will be possible to doped the nanocrystals. We have done preliminary experiments which show encouraging results while used a biphasic mixture with the nanocrystals in the non polar solvent and the silver precursor in the polar solvent.
- The introduction of impurities in a shell whose growth will be done on nanocrystals cores preliminary synthesized at high temperature. Indeed, nowaday the most performing syntheses to get monodisperses and cristallins nanocrystals are set at high temperature, on the other hand we have shown that shells grown at low temperature exhibit properties equivalent to those made at high temperature. So, the doping will be done in a shell either of the same material (homostructures) or a different materal (heterostructure) as the core material. The precursors are salts solubles in polar solvent and the growth will be done either in biphasic medium with the nanocrystals in non polar solvent or in monophasic medium with both the nanocrystals and the precursors in the polar solvent.
The success of nanocrystals doping will be check by different techniques, including Inductively Coupled Plasma Mass Spectroscopy and X Ray Photoelectron Spectroscopy. If the impurities are magnetic, we will detect them by Electron Resonance Paramagnetic. Finally if these are electric dopants, we will study the infrared spectrometry to high light the new intraband transitions. The absorbance and emission spectroscopy will also be done as much as the microscopic characterizations.
Finally, the electrical doping will be intensively study thanks to the fabrication of devices such as field effect transistos to get informations such as the nature of the carriers which lead to transport (p doping (holes) or n doping (electrons)), their mobilities and their densities. In the long term, these kind of nanocrystals will be used in optoelectronic devices such as diodes.