Abstract
Semiconductor heterostructure nanocrystals, especially with core/shell architectures, are important for numerous applications. Here we show that by decreasing the shell growth rate the morphology of ZnS shells on ZnSe quantum rods can be tuned from flat to islands-like, which decreases the interfacial strain energy. Further reduced growth speed, approaching the thermodynamic limit, leads to coherent shell growth forming unique helical-shell morphology. This reveals a template-free mechanism for induced chirality at the nanoscale. The helical morphology minimizes the sum of the strain and surface energy and maintains band gap emission due to its coherent core/shell interface without traps, unlike the other morphologies. Reaching the thermodynamic controlled growth regime for colloidal semiconductor core/shell nanocrystals thus offers morphologies with clear impact on their applicative potential.
Highlights
Semiconductor heterostructure nanocrystals, especially with core/shell architectures, are important for numerous applications
Flat shell growth is desired for surface passivation, in analogy to quantum wells grown via precursor deposition from the gas phase as applied in Molecular Beam Epitaxy (MBE) layer-by-layer for two semiconductors with small lattice mismatch[7]
ZnSe nanorods passivated by organic ligands were synthesized firstly via oriented attachment, to serve as a model system[13]
Summary
Semiconductor heterostructure nanocrystals, especially with core/shell architectures, are important for numerous applications. When zinc oleate with a 1/4 molar ratio between zinc and oleic acid was used, the thickness of the ZnS shell steadily increased upon the addition of precursors (Supplementary Fig. 2). By reducing the reactivity (using zinc oleate with a 1/6.3 molar ratio between zinc and oleic acid)[18], ZnSe nanorods with a thin ZnS shell are obtained initially in the first 60 min (Fig. 1c).
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