2D Quantum Dot Research Articles

Highly Tunable 2D Silicon Quantum Dot Array with Coupling beyond Nearest Neighbors.

Scaling up quantum dots to two-dimensional (2D) arrays is a crucial step for advancing semiconductor quantum computation. However, maintaining excellent tunability of quantum dot parameters, including both nearest-neighbor and next-nearest-neighbor couplings, during 2D scaling is challenging, particularly for silicon quantum dots due to their relatively small size. Here, we present a highly controllable and interconnected 2D quantum dot array in planar silicon, demonstrating independent control over electron fillings and the tunnel couplings of nearest-neighbor dots. More importantly, we also demonstrate the wide tuning of tunnel couplings between next-nearest-neighbor dots, which play a crucial role in 2D quantum dot arrays. This excellent tunability enables us to alter the coupling configuration of the array as needed. These results open up the possibility of utilizing silicon quantum dot arrays as versatile platforms for quantum computing and quantum simulation.

Performance of Low-Dimensional Solid Room-Temperature Photodetectors-Critical View.

In the last twenty years, nanofabrication progress has allowed for the emergence of a new photodetector family, generally called low-dimensional solids (LDSs), among which the most important are two-dimensional (2D) materials, perovskites, and nanowires/quantum dots. They operate in a wide wavelength range from ultraviolet to far-infrared. Current research indicates remarkable advances in increasing the performance of this new generation of photodetectors. The published performance at room temperature is even better than reported for typical photodetectors. Several articles demonstrate detectivity outperforming physical boundaries driven by background radiation and signal fluctuations. This study attempts to explain these peculiarities. In order to achieve this goal, we first clarify the fundamental differences in the photoelectric effects of the new generation of photodetectors compared to the standard designs dominating the commercial market. Photodetectors made of 2D transition metal dichalcogenides (TMDs), quantum dots, topological insulators, and perovskites are mainly considered. Their performance is compared with the fundamental limits estimated by the signal fluctuation limit (in the ultraviolet region) and the background radiation limit (in the infrared region). In the latter case, Law 19 dedicated to HgCdTe photodiodes is used as a standard reference benchmark. The causes for the performance overestimate of the different types of LDS detectors are also explained. Finally, an attempt is made to determine their place in the global market in the long term.

Chirality of CsPbBr3 Nanocrystals with Varying Dimensions in the Presence of Chiral Molecules.

Chiral lead halide perovskite (LHP) nanocrystals (NCs) have been attracting considerable interest for circularly polarized luminescence (CPL)-based optoelectronic applications. This study combined experimental and computational analyses to investigate how the dimensionality of 3D (cubic) to 0D (quantum dots) influences the tunable chiral emission of CsPbBr3 LHP NCs. The circular dichroism (CD) spectra have a significant blue shift from 508 to 406 nm. The dissymmetry factors for CD (gCD) change from ±2.5 × 10-3 to ±7.5 × 10-3 as dimensionality varies from 3D to 0D in the presence of the chiral molecule (cyclohexylethylamine, CHEA). A significant luminescence dissymmetry factor (glum) of ±5.6 × 10-4 is observed in the 0D CsPbBr3 NCs. Theoretical calculations using structural distortion parameters, the extent of charge transfer, and electrostatic potential profiles have revealed that the most significant enhancement of the chirality transfer occurs from the CHEA molecules to 0D NCs, and the order of chirality transfer from CHEA to CsPbBr3 NCs is 0D (quantum dots) > 2D (nanoplatelet) > 3D (cubic).

DFT formalism studies on the structural and electronic properties of hexagonal graphene quantum dot with B, N and Si substitutional impurities

The study of carbon-based nanostructured materials is a highly active research field, that has made significant progress in the study of twodimensional materials and nanotechnology. The interest in these materials is mainly attributed to the fascinating properties they exhibit, as seen in the case of graphene as a 2D material, as well as emergence on numerous novel 2D materials and their heterostructures. Additionally, there is important interest in systems such as 2D quantum dots. Therefore, this work focuses on the systematic study of graphene quantum dots of various sizes, all within the framework of first-principles density functional theory. We started with the simplest graphene quantum dot (GQD) structure, benzene (C6H6), which consist of six carbon atoms passivated with hydrogen atoms. We then increased its size by adding more aromatic rings, resulting in the following GQD configurations: C24H12, C54H18, C96H24, C150H30 and C216H36. We report the density of states (DOS) and the imaginary part of the dielectric function (ε2) for the system, analyzing both the pristine configuration and the effect of both single and double (boron, nitrogen and silicon, denoted as Sa). The double substitutional atom study was done considering random, ortho-, meta-, and para-director positions just for the C94H24Sa2 GQD. In general, we can conclude that as the GQD increases in size, the HOMO-LUMO energy decreases. Furthermore, it is observed that boron and nitrogen exhibit their expected n-, and p-type doping characteristics, but this differs between single and double Sa substitutions. Additionally, the imaginary part of the dielectric function is highly sensitive to the positions of single and double substitutional atoms, as well as the polarization of incident light. Therefore, we suggest that these differences can be used to clearly determinate the type of substitutional atoms and their positions from optical measurements.

Synthesis and Performance Study of Photodetectors of Low-Dimensional Perovskites

This paper reviews the recent advancements in perovskite-structured photodetectors, highlighting the significance of their dimensional variations, which range from 0D quantum dots to 1D nanowires and microwires, and further to 2D nanostructures. It examines the various synthesis and modification techniques used to optimize these structures, along with their compositional variations. Additionally, the paper assesses the photodetection performance of these devices and explores their potential applications. Furthermore, a comprehensive summary of the key quality factors for photodetectors, the unique photoelectric properties of low-dimensional perovskites, and the methods for their synthesis is provided, offering a comprehensive overview of the current research landscape in this field.

Construction of a 3D Quantum Dot Nanoassembly with Two-Step FRET for One-Step Sensing of Human Telomerase RNA in Breast Cancer Cells and Tissues.

Telomerase is an important biomarker for early diagnosis of cancers, but current telomerase assays usually rely on measuring the extension products of telomerase substrates, which increases the assay complexity. More evidence indicates that human telomerase RNA (hTR), as a core component of telomerase, is positively correlated with the telomerase activity. Herein, we demonstrate the development of a duplex-specific nuclease (DSN)-propelled 3D quantum dot (QD) nanoassembly with two-step Föster resonance energy transfer (FRET) for the one-step sensing of hTR in breast cancer cells and tissues. This assay involves only one hairpin probe modified with a Cy5 at the sixth base from the 5'-biotin end and a BHQ2 at the 3'-terminus, which integrates three functions of target recognition, target recycling amplification, and signal readout. The anchoring of the hairpin probe on the 605QD surface results in the formation of a 3D 605QD-Cy5-probe-BHQ2 nanoassembly in which two-step FRET occurs among the 605QD, Cy5, and BHQ2 quencher. Notably, the formation of 605QD-Cy5-probe-BHQ2 nanoassembly facilitates the reduction of background signal and the increase of signal-to-background ratio due to its dense, highly oriented nucleic acid shell-induced steric hindrance effect. This assay can achieve one-step and rapid detection of hTR with a detection limit of 2.10 fM, which is the simplest and most rapid hTR assay reported so far. Moreover, this assay can efficiently distinguish single-base mismatched sequences, and it can discriminate the hTR level between breast cancer patients and healthy donors with a high accuracy of 100%, with great prospects for early diagnosis of cancers.

Charge Transfer from Quantum-Confined 0D, 1D, and 2D Nanocrystals.

The properties of colloidal quantum-confined semiconductor nanocrystals (NCs), including zero-dimensional (0D) quantum dots, 1D nanorods, 2D nanoplatelets, and their heterostructures, can be tuned through their size, dimensionality, and material composition. In their photovoltaic and photocatalytic applications, a key step is to generate spatially separated and long-lived electrons and holes by interfacial charge transfer. These charge transfer properties have been extensively studied recently, which is the subject of this Review. The Review starts with a summary of the electronic structure and optical properties of 0D-2D nanocrystals, followed by the advances in wave function engineering, a novel way to control the spatial distribution of electrons and holes, through their size, dimension, and composition. It discusses the dependence of NC charge transfer on various parameters and the development of the Auger-assisted charge transfer model. Recent advances in understanding multiple exciton generation, decay, and dissociation are also discussed, with an emphasis on multiple carrier transfer. Finally, the applications of nanocrystal-based systems for photocatalysis are reviewed, focusing on the photodriven charge separation and recombination processes that dictate the function and performance of these materials. The Review ends with a summary and outlook of key remaining challenges and promising future directions in the field.

DNA Linked Mixed-Dimensional Heterostructures: The Designing, Nanoscale Control and Device Applications of Tmdc-Quantum Dot Nanohybrids

DNA Linked Mixed-Dimensional Heterostructures: the Designing, Nanoscale Control and Device Applications of TMDC-Quantum Dot Nanohybrids Kai Chen,a Teymour Talha-Dean,b Tingting Zheng, a Stoichko Dimitrov, a Jan Mol b and Matteo Palma a aDepartment of chemistry, Queen Mary University of London, London E1 4NS, United Kingdom bDepartment of Physics, Queen Mary University of London, London E1 4NS, United KingdomThe construction of mixed-dimensional heterostructures is a promising approach for the development of biosensing and optoelectronic systems and devices. The accurate nanoscale control of the heterostructures interface is a key challenge, for instance to tune the distance between the individual components and their stoichiometry, that in turn affect their electronic coupling. In this regard, DNA can be a powerful structural and functional linker for nano-hybrids assembly, due to its tunability down to sub-nanometer control.Our current interest is focused on the fabrication of TMDC-based nanohybrids using double stranded (ds) DNA as both a linker and templating moiety. In particular, we recently employed three different approaches to functionalize the surface of MoS2 nanoflakes and assembled 0D (quantum dots)/2D (MoS2 flakes) hybrids using DNA as a connection moiety (see figure).[1] DNA allowed us to control the distance between QDs and MoS2 with sub-nanoscale accuracy, allowing the fine tuning of the electronic coupling between the two nanostructures.We will further discuss the construction of mixed-dimensional nanohybrids i) via the use different DNA nanotechnology strategies, and ii) for the fabrication of responsive optoelectronic devices. [1] T. Talha-Deam, K. Chen, G. Mastroianni, F. Gesuele, J. Mol and M. Pamla. “Nanoscale Control of DNA-Linked MoS2-Quantum Dot Heterostructures”. Bioconjugate Chemistry, 2022, DOI: 10.1021/acs.bioconjchem.2c00285

A 2D quantum dot array in planar 28Si/SiGe

Semiconductor spin qubits have gained increasing attention as a possible platform to host a fault-tolerant quantum computer. First demonstrations of spin qubit arrays have been shown in a wide variety of semiconductor materials. The highest performance for spin qubit logic has been realized in silicon, but scaling silicon quantum dot arrays in two dimensions has proven to be challenging. By taking advantage of high-quality heterostructures and carefully designed gate patterns, we are able to form a tunnel coupled 2 × 2 quantum dot array in a 28Si/SiGe heterostructure. We are able to load a single electron in all four quantum dots, thus reaching the (1,1,1,1) charge state. Furthermore, we characterize and control the tunnel coupling between all pairs of dots by measuring polarization lines over a wide range of barrier gate voltages. Tunnel couplings can be tuned from about 30 μeV up to approximately 400 μeV. These experiments provide insightful information on how to design 2D quantum dot arrays and constitute a first step toward the operation of spin qubits in 28Si/SiGe quantum dots in two dimensions.

Photoresponsivity Enhancement of Monolayer MoS2 by Silicon Quantum Dots

Hybrid 2D/0D structures with various 2D materials and 0D quantum dots (QDs) have been studied to overcome the limitations of 2D materials. In this work, a hybrid structure with MoS2 and silicon quantum dots (Si QDs) as a photodetector is developed. The I–V transfer characteristics show a threshold voltage shift after decorating Si QDs on MoS2, which results from an n‐type doping effect to the MoS2 channel from the Si QDs. The field‐effect mobility of the MoS2/Si QDs device is increased by ≈5.8 times compared with that of the bare MoS2 device. It is understood that the mobility enhancement is attributed to the surface defect passivation of MoS2 at the interface with Si QDs. It is observed that the photoresponsivity of the MoS2/Si QDs structure is improved by ≈7.7 times compared with that of the bare MoS2 device under 500 nm illumination. Additionally, it is observed that the photoluminescence (PL) intensity of MoS2 is increased about 4.5 times after decoration of Si QDs. The band alignment as type I at the interface between the Si QDs and MoS2 is interpreted. The mobility enhancement and the photoexcited charge transfer (CT) between the MoS2 and the Si QDs due to the illumination lead to enhancing the photoresponsivity of the MoS2/Si QDs hybrid structure.

Enhanced Modulation Bandwidth by Integrating 2D Semiconductor and Quantum Dots for Visible Light Communication

Light‐emitting devices present a tremendous potential for visible light communication (VLC) due to their dual functionality as both communication and lighting devices. Herein this study, the significant enhancement in VLC modulation bandwidth by integrating two‐dimensional (2D) semiconductor and quantum dots (QDs) emitter is reported. Generally, the modulation bandwidth of CdSe‐based QDs is limited to only less than 25 MHz; however, with the proposed hybrid emitter, a maximum modulation bandwidth of 130 MHz for CdSe/ZnS QDs emitter is able to be achieved. The WSe2 monolayer is integrated into an Au–nanorod–decorated CdSe/ZnS QDs emitter to achieve high modulation performance. The modulation bandwidth of the hybrid QD–Au–WSe2 emitter (130 MHz) is found to be higher than those of the pristine QDs and QD–WSe2 heterostructure without Au nanorods (79 and 91 MHz, respectively). A significant increase is observed in the transition rate of QDs excitons when they are integrated with Au nanorods and WSe2 monolayer, which is substantiated by a reduction in average carrier lifetime from time‐resolved photoluminescence analysis. This approach and the findings open an opportunity to apply 2D semiconductors into the next‐generation miniature VLC devices, for high‐speed optical communications.

Advances in Heterostructures for Optoelectronic Devices: Materials, Properties, Conduction Mechanisms, Device Applications.

Atomically thin 2D transition metal dichalcogenides (TMDs) have recently been spotlighted for next-generation electronic and photoelectric device applications. TMD materials with high carrier mobility have superior electronic properties different from bulk semiconductor materials. 0D quantum dots (QDs) possess the ability to tune their bandgap by composition, diameter, and morphology, which allows for a control of their light absorbance and emission wavelength. However, QDs exhibit a low charge carrier mobility and the presence of surface trap states, making it difficult to apply them to electronic and optoelectronic devices. Accordingly, 0D/2D hybrid structures are considered as functional materials with complementary advantages that may not be realized with a single component.Such advantages allow them to be used as both transport and active layers in next-generation optoelectronic applications such as photodetectors, image sensors, solar cells, and light-emitting diodes. Here, recent discoveries related to multicomponent hybrid materials are highlighted. Research trends in electronic and optoelectronic devices based on hybrid heterogeneous materials are also introduced and the issues to be solved from the perspective of the materials and devices are discussed.

Lithium Azides Induced SnS Quantum Dots for Ultra-Fast and Long-Term Sodium Storage.

Tin sulfide (SnS) is an attractive anode for sodium ion batteries (NIBs) because of its high theoretical capacity, while it seriously suffers from the inherently poor conductivity and huge volume variation during the cycling process, leading to inferior lifespan. To intrinsically maximize the sodium storage of SnS, herein, lithium azides (LiN3 )-induced SnS quantum dots (QDs) are first reported using a simple electrospinning strategy, where SnS QDs are uniformly distributed in the carbon fibers. Taking the advantage of LiN3 , which can effectively prevent the growth of crystal nuclei during the thermal treatment, the well-dispersed SnS QDs performs superior Na+ transfer kinetics and pseudocapacitive when used as an anode material for NIBs. The 3D SnS quantum dots embedded uniformly in N-doped nanofibers (SnS QDs@NCF) electrodes display superior long cycling life-span (484.6mAhg-1 after 5800 cycles at 2Ag-1 and 430.9mAhg-1 after 7880 cycles at 10Ag-1 ), as well as excellent rate capability (422.3mAhg-1 at 20Ag-1 ). This fabrication of transition metal sulfides QDs composites provide a feasible strategy to develop NIBs with long life-span and superior rate capability to pave its practical implementation.

Duplex-specific nuclease powered 3D DNA walker and quantum dots barcodes for homogeneous electrochemical detection of microRNAs

Multiplex microRNAs (miRNAs) detection is beneficial for early diagnosis and prognosis of cancer. Herein, duplex-specific nuclease (DSN) powered 3D DNA walker and quantum dots (QDs) barcodes were designed for the simultaneous detection of miRNAs in a homogeneous electrochemical sensor. In the proof-of-concept experiment, the effective active area of the as-prepared graphene aerogel-modified carbon paper (CP-GAs) electrode was ∼14.30 times larger than that of the traditional glassy carbon electrode (GCE), endowing the enhanced capability of loading more metal ions for ultrasensitive detection of miRNAs. In addition, DSN-powered target recycling and DNA walking strategy assured the sensitive detection of miRNAs. After the introduction of magnetic beads (MNs) and electrochemical double enrichment strategies, the integration of triple signal amplification methods yielded good detection results. Under optimal conditions, towards simultaneous detection of microRNA-21 (miR-21) and miRNA-155 (miR-155), a linear range of 10−16–10−7 M and a sensitivity of 10 aM (miR-21) and 2.18 aM (miR-155) were achieved, respectively. It was worth mentioning that the prepared sensor can detect miR-155 down to 0.17 aM, which was also extremely advantageous among the sensors reported so far. What's more, through verification, the prepared sensor had good selectivity and reproducibility, and exhibited good detection ability in complex serum environments, showing great potential in early clinical diagnosis and screening.

Graphene/III–V Quantum Dot Mixed-Dimensional Heterostructure for Enhanced Radiative Recombinations via Hole Carrier Transfer

Fabrication of high quantum efficiency nanoscale device is challenging due to increased carrier loss at surface. Low dimensional materials such 0D quantum dots and 2D materials have been widely studied to mitigate the loss. Here, we demonstrate a strong photoluminescence enhancement from graphene/III-V quantum dot mixed-dimensional heterostructures. The distance between graphene and quantum dots in the 2D/0D hybrid structure determines the degree of radiative carrier recombination enhancement from 80% to 800% compared to the quantum dot only structure. Time-resolved photoluminescence decay also shows increased carrier lifetimes when the distance decreases from 50 to 10 nm. We propose that the optical enhancement is due to energy band bending and hole carrier transfer, which repair the imbalance of electron and hole carrier densities in quantum dots. This 2D graphene/0D quantum dot heterostructure shows promise for high performance nanoscale optoelectronic devices.

Probing the dipole–dipole interaction in single 0D/2D heterostructures by tightly focused cylindrical vector beams

Energy transfer from zero-dimensional (0D) quantum dots (QDs) to two-dimensional (2D) materials has attracted much attention for both the manipulation of fundamental material properties and their potential device applications. An understanding of the effect of dipole interactions on energy transfer rate in the hybrid dimensional system is essential for improving optoelectronic device performance. Here, we report the dipole-orientation-dependent energy transfer from individual core–shell CdSe/ZnS QDs to bilayer molybdenum disulfide (MoS2) by utilizing tightly focused azimuthally and radially polarized cylindrical vector beams. With second-order photon correlation measurements [g2(τ)], we show the single-photon emission behavior from QDs in 0D/2D heterostructures, indicating that the investigated heterostructure is constructed from single QDs. By polarization resolved photoluminescence (PL) imaging and PL lifetime measurements, we observe a fast energy transfer rate of the system excited with azimuthally polarized beams and interpret it based on dipole–dipole interactions with Förster energy transfer theory. Our work provides an in-depth understanding of the dipole-orientation-dependent energy transfer mechanism in 0D/2D systems, which could offer guidance for designing the related optoelectronic device applications.

Phase Dependent Parity Time Symmetry in a quantum dot nanostructure

We present a diamond configuration quantum dots nanostructure trapped in two-dimensional (2D) optical lattices for the investigation of parity time (PT) symmetry. We trap quantum dots in a Gaussian density distribution to examine the PT, non-PT, and anti-PT symmetry in periodic 2D optical lattices. The variation in the relative phase of the optical beams in the quantum dots spectrum indicates either PT, anti-PT, or non-PT symmetry, resulting in an intriguing modulation of imaginary and real refractive index (RI) components. Controlling the appropriate modulation of the RI leads in PT symmetry being controlled by a single parameter, the relative phase of the optical fields. Using detuning and the coupling field of Rabi frequencies, we may determine the state of PT symmetry as well as the direction of field propagation. Coherent control of PT symmetry in 2D quantum dot nanostructure trapped in optical lattices may also have applications in 2D optical devices such as diodes, modulators and photonic transistors.

Room‐Temperature NH3 Sensor Based on SnO2 Quantum Dots Functionalized SnS2 Nanosheets

AbstractTraditional metal oxide semiconductor gas sensors are facing significant challenges for portable devices and integration due to large power consumption caused by high working temperature. 2D nanomaterials with large specific surface areas, rich active sites, and tunable electrical properties are proved to be promising candidates for room‐temperature gas sensors. However, several disadvantages including weak response, sluggish response/recovery kinetics, and poor selectivity still need to be overcome for high‐performance gas sensors. Herein, SnO2 quantum dots (QDs) with a diameter of ≈3 nm functionalized SnS2 nanosheets with a thickness of ≈17 nm are synthesized via a two‐step solvothermal method, which exhibits a high response of 11.1 to 100 ppm NH3 at room temperature of 25 °C with fast response speed and good repeatability, high selectivity, and long‐term stability. The sensing mechanism is mainly ascribed to 0D/2D heterostructure, synergistic effect, and n‐n heterojunction constructed across the interfaces between SnO2 QDs and SnS2 nanosheets. The as‐prepared nanomaterials may contribute to the reasonable design of heterostructure between 0D QDs and 2D nanomaterials, and offer a promising candidate for room‐temperature NH3 detection.

Studies on the optical stability of CsPbBr3 with different dimensions (0D, 1D, 2D, 3D) under thermal environments.

The thermal stability of phosphor materials had long been a bottleneck in their commercialization. Nowadays, cesium lead halide perovskite CsPbBr3 has been considered a potential replacement for the next generation of optoelectronic devices due to its excellent optical and electronic properties, however, the devices inevitably generate high temperatures on the surface under prolonged energization conditions in practical applications, which can be fatal to CsPbBr3. Despite the various strategies that have been employed to improve the thermal stability of CsPbBr3, systematic studies of the thermal stability of the basis CsPbBr3 are lacking. In this study, CsPbBr3 with different dimensions (0D quantum dots (QDs), 1D nanowires (NWs), 2D nanoplate (NPs), 3D micron crystals (MCs)) was prepared by traditional high-temperature thermal injection, and a systematic study was carried out on their optical properties and thermal stability. The results revealed that the dimensional change will directly influence the optical properties as well as the thermal stability of CsPbBr3. In particular, 3D CsPbBr3 MCs maintained relatively high thermal stability under high-temperature environments, which will bring interest for the commercialization of next-generation perovskite optoelectronic devices.

Two-dimensional bismuth oxyselenide quantum dots as nanosensors for selective metal ion detection over a wide dynamic range: sensing mechanism and selectivity.

Bismuth oxyselenide (Bi2O2Se) nanosheets, a new 2D non-van der Waals nanomaterial having unique semiconducting properties, could be favorable for various sensing applications. In the present report, a top-down chemical approach was adopted to synthesize ultrathin Bi2O2Se quantum dots (QDs) in an appropriate solution. The as-prepared 2D Bi2O2Se QDs with an average size of ∼3 nm, exhibiting strong visible fluorescence, were utilized for heavy-metal ion detection with high selectivity. The QDs show a high optical band gap and a reasonably high fluorescence quantum yield (∼4%) in the green region without any functionalization. A series of heavy metal ions were detected using these QDs. The as-prepared QDs exhibit selective detection of Fe3+ over a wide dynamic range with a high quenching ratio and a low detection limit (<0.5 μM). The mechanism of visible fluorescence and Fe3+ ion-induced quenching was investigated in detail based on a model involving adsorption and charge transfer. Density functional theory (DFT) first principles calculations show that fluorescence quenching occurred selectively due to the efficient trapping of electrons in the bandgap states created by the Fe atoms. This work presents a sustainable and scalable method to synthesize 2D Bi2O2Se QDs for heavy metal ion sensing over a wide dynamic range and these 2D QDs could find potential uses in gas sensors, biosensors and optoelectronics.