Atomically flat semiconductor nanoplatelets – SNAP

This project is centered the study of a new generation of colloidal semiconductor nanoparticles: the nano-platelets. These objects are atomically flat with highly anisotropic shapes: their lateral dimensions can be 100 times larger than their thickness. The nano-platelets can be synthesized in solution at low temperature and their thickness can be tuned with atomic precision. The team leading this project was the first to synthesize them and is devoting a great deal of efforts on the study of these objects. The nanoplatelets exhibit a large 1 dimensional quantum confinement in the thickness direction while the lateral confinement is almost negligible. The physics of these objects is very similar to the one of quantum wells grown by MBE or MOCVD. As a matter of fact, we have recently shown that the nano-platelets have similar optical absorption than that of quantum wells. We have also shown that their fluorescence lifetimes were much faster than those usually reported for other colloidal nanoparticles. This novel type of nano-objects has been synthesized in three different materials: CdSe, CdS and CdTe. In the three cases, the crystal phase of the nano-platelets is zinc blend. In this project, we propose to investigate the formation mechanisms of the nano-platelets, to extend their synthesis to other materials, and to generate nano-platelets with hetero-structures. At a spectroscopic level, we will characterize further the giant oscillator transition strength recently observed in these structures. To do so, we will characterize these nano-platelets spectroscopically for various lateral dimensions in ensemble measurements but also using single particle spectroscopy. We will also study the memory of the spin polarization in the nano-platelets. On a theoretical level, we will study both the optical and the mechanical properties of the nano-platelets. This will be done using an ab initio approach (codes ABINIT, SIESTA) to tackle the relaxation of the atomic positions, combined with tight binding calculations to grasp the electronic and optical properties of the nano-platelets