Quantum coupling in colloidal homodimers of epitaxially attached CdSe@CdS dot@platelets probed on single-particle level

Coupled quantum-dot (QD) dimers can be viewed as diatomic artificial molecules, thus offering a unique platform to study molecular physics and quantum phenomena. However, controlled synthesis of QD dimers has remained an outstanding experimental challenge, given necessary construction of hundreds of lattice bonds at the neck between two QDs with a unique attachment axis. Here, QD homodimers are synthesized in solution with a high yield by the epitaxial attachment of two monodisperse CdSe@CdS dot@platelet QDs along their common <11 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mover><mml:mrow><mml:mn>2</mml:mn></mml:mrow> <mml:mo>¯</mml:mo></mml:mover> </mml:math> 0> axis. The exact construction of hundreds of lattice bonds in the epitaxial neck are enabled by the large (11 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mover><mml:mrow><mml:mn>2</mml:mn></mml:mrow> <mml:mo>¯</mml:mo></mml:mover> </mml:math> 0) side facets with ideal lattice match between two epitaxial QDs and limited ligands passivation, resulting in controlled spacing between two core QDs (core-spacing). Single-particle spectroscopy reveals that the photoluminescence (PL) of single homodimer with a small core-spacing (7.8 nm) is split into two room-temperature resolvable peaks, consistent with strongly-split bonding and antibonding electron orbitals of "artificial diatomic molecules". The two peaks of the split PL are orthogonally-polarized, and two types of molecular bi-excitons are observed for the homodimer. These advancements lay a viable foundation for controllable construction of "artificial molecules" in solution.