Core/Shell Colloidal Semiconductor\nNanoplatelets

Abstract

We have recently synthesized atomically flat semiconductor\ncolloidal\nnanoplatelets with quasi 2D geometry. Here, we show that core/shell\nnanoplatelets can be obtained with a 2D geometry that is conserved.\nThe epitaxial growth of the shell semiconductor is performed at room\ntemperature. We report the detailed synthesis of CdSe/CdS and CdSe/CdZnS\nstructures with different shell thicknesses. The shell growth is characterized\nboth spectroscopically and structurally. In particular, the core/shell\nstructure appears very clearly on high-resolution, high-angle annular\ndark-field transmission electron microscope images, thanks to the\ndifference of atomic density between the core and the shell. When\nthe nanoplatelets stand on their edge, we can precisely count the\nnumber of atomic planes forming the core and the shell. This provides\na direct measurement, with atomic precision, of the core nanoplatelets\nthickness. The constraints exerted by the shell growth on the core\nis analyzed using global phase analysis. The core/shell nanoplatelets\nwe obtained have narrow emission spectra with full-width at half-maximum\nclose to 20 nm, and quantum yield that can reach 60%.