Coupled Colloidal Quantum Dot Molecules

Seminar | October 1 | 4-5 p.m. | 120 Latimer Hall

 Uri Banin, Institute of Chemistry & The Center for Nanoscience and Nanotechnology, The Hebrew University of Jerusalem

 College of Chemistry

Colloidal semiconductor Quantum Dots (CQDs) that contain hundreds to thousands of atoms manifest size dependent tunable properties and have reached an exquisite level of control, leading to their technological applications in optoelectronics and bioimaging. Considering them as artificial atoms, CQD molecules connected with molecular linkers such as DNA strands were studied. Yet, in these structures the presence of a high potential barrier limits coupling between the quantum states of neighboring CQDs limiting their full potential as coupled systems. Although coupled quantum dots were prepared by means of molecular beam epitaxy (MBE), their typical dimensions limit coupling to small energy scales suitable to low temperature operation. Furthermore, while MBE grown structures are inherently buried within a host semiconductor, CQDs are free in solution and accessible for wet-chemical manipulations.
Herein, we introduce a facile and powerful strategy for coupled CQDs molecules with precise control over the composition and size of the barrier in between the artificial atoms to allow for tuning the electronic coupling characteristics and their optical properties. Our approach entails fusing two CdSe/CdS core/shell CQDs via constrained oriented attachment. This yields a dimer with a tailored barrier dictated by the shell composition, thickness and fusion reaction conditions. The possible nanocrystal facets in which such fusion takes place are analysed with atomic resolution revealing the distribution of possible crystal fusion scenarios. Coherent coupling is revealed by ensemble and single particle spectroscopic signatures, in agreement with quantum mechanical simulations.

This sets the stage for nanocrystals chemistry to yield a diverse selection of coupled CQD molecules utilizing the rich collection of ubiquitous artificial atom core/shell CQD building blocks. Such CQD molecules are of direct relevance for numerous applications including in displays, sensing, biological tagging and emerging quantum technologies.

Acknowledgment: The research leading to these results has received financial support from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme (grant agreement No. [741767]).