A case study of ALD encapsulation of quantum dots: embedding supported CdSe/CdS/ZnS quantum dots in a ZnO matrix

We study the encapsulation of monolayers of CdSe/CdS/ZnS core/shell/shell quantum dots (QDs) in a ZnO matrix by atomic layer deposition (ALD) in order to gain insight in the interaction between quantum dots and ALD precursors and the resulting metal oxide coating. Using in situ XRF and GISAXS, we show the inhibition of ZnO growth on as-deposited QDs. Growth can, however, be triggered by exposing the QDs to a single pulse of trimethylaluminum (TMA) vapor. Such a TMA pretreatment results in the substitution of 35-40% of the surface Zn by Al. Whereas this drops by half the photoluminescence quantum yield of the QDs, we argue that this replacement primes the QD monolayer for ZnO growth by ALD. Finally, the evolution of the GISAXS pattern during subsequent ALD growth attests the preservation of the ordering of the QDs in the monolayer. These results illustrate the important interplay between highly reactive ALD precursors and the QD surface