[Paper Review] Coupled Colloidal Quantum Dot Molecules

Jiabin Cui, Yossef E. Panfil+7 more|arXiv (Cornell University)|May 15, 2019

Quantum Dots Synthesis And Properties9 references34 citations

TL;DR

The paper demonstrates coherent coupling of CdSe/CdS core/shell nanocrystals formed into dimers via constrained oriented attachment, showing a band-gap red shift and wavefunction hybridization, investigated by single-particle spectroscopy.

ABSTRACT

Coupling of atoms is the basis of chemistry, yielding the beauty and richness of molecules. We utilize semiconductor nanocrystals as artificial atoms to form nanocrystal molecules that are structurally and electronically coupled. CdSe/CdS core/shell nanocrystals are linked to form dimers which are then fused via constrained oriented attachment. The possible nanocrystal facets in which such fusion takes place are analyzed with atomic resolution revealing the distribution of possible crystal fusion scenarios. Coherent coupling and wavefunction hybridization are manifested by a red shift of the band gap, in agreement with quantum mechanical simulations. Single nanoparticle spectroscopy unravels the attributes of coupled nanocrystal dimers related to the unique combination of quantum mechanical tunneling and energy transfer mechanisms. This sets the stage for nanocrystals chemistry to yield a diverse selection of coupled nanocrystal molecules constructed from controlled core/shell nanocrystal building blocks. These are of direct relevance for numerous applications in displays, sensing, biological tagging and emerging quantum technologies.

Motivation & Objective

• Motivate the use of semiconductor nanocrystals as artificial atoms to build nanocrystal molecules.
• Identify structural fusion pathways and facets enabling coupling in CdSe/CdS core/shell dimers.
• Characterize electronic coupling through optical signatures and quantum-mechanical simulations.
• Establish connections between coupling mechanisms (tunneling, energy transfer) and observable spectra.
• Highlight potential applications in displays, sensing, biology tagging, and quantum technologies.

Proposed method

• Link CdSe/CdS core/shell nanocrystals into dimers.
• Fuse dimers through constrained oriented attachment to form coupled nanocrystal molecules.
• Analyze possible fusion facets at atomic resolution to map fusion scenarios.
• Observe coherent coupling and wavefunction hybridization via a red shift of the band gap.
• Perform quantum mechanical simulations to support the experimental observations.
• Use single nanoparticle spectroscopy to study coupling-related attributes (tunneling and energy transfer).

Experimental results

Research questions

• RQ1 How can core/shell CdSe/CdS nanocrystals be assembled into structurally and electronically coupled dimers?
• RQ2 What are the crystal facets and fusion pathways that enable effective coupling between nanocrystals?
• RQ3 What optical signatures indicate coherent coupling and wavefunction hybridization in coupled nanocrystal molecules?
• RQ4 How do tunneling and energy transfer contribute to the observed spectroscopy of coupled dimers?
• RQ5 What are the potential applications of coupled nanocrystal molecules in technology and biology?

Key findings

• Coupled CdSe/CdS nanocrystal dimers exhibit coherent coupling and wavefunction hybridization.
• A red shift of the band gap is observed, consistent with quantum mechanical simulations.
• Facet- and orientation-controlled fusion via constrained oriented attachment reveals possible fusion scenarios.
• Single nanoparticle spectroscopy uncovers attributes related to quantum tunneling and energy transfer in the dimers.
• The work demonstrates a pathway to construct diverse coupled nanocrystal molecules from controlled building blocks.