2D materials are a family of layered materials exhibiting rich exotic phenomena, such as valley‐contrasting physics. Down to single‐particle level, unraveling fundamental physics and potential applications including quantum information processing in these materials attracts significant research interests. To unlock these great potentials, gate‐controlled quantum dot architectures have been applied in 2D materials and their heterostructures. Such systems provide the possibility of electrical confinement, control, and manipulation of single carriers in these materials. In this review, efforts in gate‐controlled quantum dots in 2D materials are presented. Following basic introductions to valley degree of freedom and gate‐controlled quantum dot systems, the up‐to‐date progress in etched and gate‐defined quantum dots in 2D materials, especially in graphene and transition metal dichalcogenides, is provided. The challenges and opportunities for future developments in this field, from views of device design, fabrication scheme, and control technology, are discussed. The rapid progress in this field not only sheds light on the understanding of spin–valley physics but also provides an ideal platform for investigating diverse condensed matter physics phenomena and realizing quantum computation in the 2D limit.

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Gate‐Controlled Quantum Dots Based on 2D Materials

Stepwise reduction of a corannulene-based helical molecular nanographene with Na metal.

Tailoring the optoelectronic properties of semiconductor quantum dots is essential for designing functionalized nanoscale devices. In this work, we use first-principles calculations to study the optoelectronic properties of small penta-graphene quantum dots (PGQDs) with various edge-functionalized groups, including hydrogen, halogen (fluorine, chlorine, and bromine), and hydroxyl functional groups. It is evident that these quantum dots, especially those passivated by hydrogen atoms, are thermally stable in vacuum. Moreover, the larger the quantum dots, the more negative the formation energy on stability could reach, thus forming thermodynamically more stable quantum dots. All investigated PGQDs exhibit semiconductor properties. Their bandgaps decrease with an increase in the size of the quantum dots, resulting from the hybridization of sp2 and sp3 carbon atoms and from the charge depletion or accumulation between the passivated atoms and the principal components upon interactions. Concurrently, this study aims to explain the optical absorption anisotropy induced by the edge-functionalized groups of PGQDs under multiple incident light polarizations. These results highlight the use of edge-functionalized groups to develop the next generation of optoelectronic devices.

https://aip.scitation.org/doi/pdf/10.1063/5.0091475

First-principles study of electronic and optical properties of small edge-functionalized penta-graphene quantum dots

Carbon quantum dots (CQDs) are remarkable nanomaterials owing to their auspicious aspects. Herein, we synthesized highly green fluorescent CQDs via a one-step facile hydrothermal method using a chicken feather as a carbon source. The synthesized CQDs have an average particle size of ∼ 5 ± 1 nm in diameter with a quantum yield of ∼ 77.2 %. As-prepared CQDs are directly used as a fluorescent probe for the sensitive and selective detection of Hg2+ ions with a detection limit of ∼ 6.2 nM. Interestingly, the above results suggested that the synthesized CQDs as a potential candidate for Hg2+ sensing application. 

A potential forecast of carbon quantum dots (CQDs) as an ultrasensitive and selective fluorescence probe for Hg (II) ions sensing

The uncertainty and quantum correlation of measurement in double quantum-dot systems

Graphene quantum dots (GQDs) not only have potential applications on spin qubit, but also serve as essential platforms to study the fundamental properties of Dirac fermions, such as Klein tunneling and Berry phase. By now, the study of quantum confinement in GQDs still attract much attention in condensed matter physics. In this article, we review the experimental progresses on quantum confinement in GQDs mainly by using scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS). Here, the GQDs are divided into Klein GQDs, bound-state GQDs and edge-terminated GQDs according to their different confinement strength. Based on the realization of quasi-bound states in Klein GQDs, external perpendicular magnetic field is utilized as a manipulation approach to trigger and control the novel properties by tuning Berry phase and electron-electron (e-e) interaction. The tip-induced edge-free GQDs can serve as an intuitive mean to explore the broken symmetry states at nanoscale and single-electron accuracy, which are expected to be used in studying physical properties of different two-dimensional materials. Moreover, high-spin magnetic ground states are successfully introduced in edge-terminated GQDs by designing and synthesizing triangulene zigzag nanographenes.

/pdf/recent-progresses-of-quantum-confinement-in-graphene-quantum-nhowfypuac.pdf

Si-Yu Li

Papers

Recent progresses of quantum confinement in graphene quantum dots