Quantum dots are materials which have their electrons confined in 3-dimensions and are often referred to as 0-dimensional. Quantum dots can aggregate together to create quantum dot arrays which possess unique quantum properties and cooperative interactions suitable for many technological applications.
Controlling the electronic barriers between quantum dots is an essential process for providing an efficient crosstalk between dots, and an international team of Researchers have now precisely engineered the barrier width in some quantum dot arrays to tune their quantum confinement properties.
Quantum dots are comparable to artificial atoms in many respects, but mainly because they confine electrons into discrete and quantized energy levels.
Quantum dots often exist as a single entity, but can be aggregated together to form quantum dot solids, with the final properties decided by the cooperative interactions between the dots in the solid array.
Quantum dot arrays require monodisperse components in order to prevent anomalous properties from occurring, but many vary in their structure.
The ability to control the width of electronic barriers is essential for creating efficient crosstalk communication pathways between the quantum units and for the engineering of 2-dimensional gases.
Scientists can tune the individual units within an array to produce variations in the barrier width and barrier amplitude, which ultimately changes the dimensions of the quantum dots to optimize the electronic interactions between units.
In this research, the team from various institutions around the world have targeted a barrier disruption path which involves the lateral stacking of individual units. To do this, the Researchers altered the barrier width in a quantum dot array composed of two haloaromatic compounds which differ by just a single atom in their structures.
The Researchers self-assembled two different hexagonal molecular networks on silver substrates (film and bulk) and utilized the (111) crystallographic plane. The two haloaromatic compounds used by the Researchers to create the arrays were 3,9-dibromodinaphtho[2,3-b:2′,3′-d]thiophene (Br-DNT) and [3,9-dibromodinaphtho[2,3-b:2′,3′-d] furan (Br-DNF).
Upon formation, the Researchers substituted a single molecule from the homoatomic array and created a pattern reminiscent of a butterfly effect. The Researchers developed quantum arrays which self-assemble with a single-molecular and double-molecular separation between identical neighbouring pores and investigated the modification of the 2-dimensional gases which occupied them.
To measure the electronic structure of the arrays, the Researchers used an experimental combination of scanning tunnelling microscopy(STM)/atomic force microscopy (AFM) (Omicron STM/AFM with a q-plus configuration) and angle resolved photoemission spectroscopy (ARPES, Phoibos150).
The Researchers also employed a combination of Plane Wave Expansion (PWE), Electron Boundary Element Method (EBEM) and density functional theory (DFT) computations to theoretically analyze the electronic structures.
The Researchers we able to show that precise engineering of the barrier width could be implemented experimentally on the surfaces of the dots by substituting just a single atom between the structures of adjacent quantum dots.
The ability to tune the width of the electronic barrier also allowed the Researchers to tune both the confinement properties and the degree of intercoupling in the quantum dot array without affecting the size of the quantum dots themselves.
The formation of a nanoporous network allowed for confinement of the two-dimensional electron gas at the surface of the array. These arrays were also found to maintain their overall interdot coupling as a result of their implementation on the surface of the silver films.
The extended and periodic nature of the array allowed for direct access to the distinct band structures and their local density of states. The Researchers confirmed this through both experimental and computational approaches providing a synergistic and fundamental insight into the intercoupling processes involved in the quantum dots.
Through the synergistic approach, the Researchers found that a reduction in the coupling, from a single-wall to a double walled network, was due to the flattening of the band dispersion and an increase in the effective mass.
The work can be now used as a way for tuning surface electronic properties and becomes a part of a quantum toolbox designed in the 1990’s.
The method will also aid in helping to generate ideas towards technologies which utilize quantum dot coupling, such as in the next generation of computers, and provides a route for achieving full control over two-dimensional electron gases.
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“Precise engineering of quantum dot array coupling through their barrier widths”- Piquero-Zulaica I., et al, Nature Communications, 2017, DOI: 10.1038/s41467-017-00872-2