Core/Shell Colloidal Semiconductor
Nanoplatelets
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Abstract
We have recently synthesized atomically flat semiconductor
colloidal
nanoplatelets with quasi 2D geometry. Here, we show that core/shell
nanoplatelets can be obtained with a 2D geometry that is conserved.
The epitaxial growth of the shell semiconductor is performed at room
temperature. We report the detailed synthesis of CdSe/CdS and CdSe/CdZnS
structures with different shell thicknesses. The shell growth is characterized
both spectroscopically and structurally. In particular, the core/shell
structure appears very clearly on high-resolution, high-angle annular
dark-field transmission electron microscope images, thanks to the
difference of atomic density between the core and the shell. When
the nanoplatelets stand on their edge, we can precisely count the
number of atomic planes forming the core and the shell. This provides
a direct measurement, with atomic precision, of the core nanoplatelets
thickness. The constraints exerted by the shell growth on the core
is analyzed using global phase analysis. The core/shell nanoplatelets
we obtained have narrow emission spectra with full-width at half-maximum
close to 20 nm, and quantum yield that can reach 60%