Spatial weak-light ring soliton in self-assembled quantum dots

By using semiclassical theory combined with multiple-scale method, we analytically study the linear absorption and the nonlinear dynamical properties in a lifetime broadened Λ-type three-level self-assembled quantum dots. It is found that this system can exhibit the transparency, and the width of the transparency window becomes wider with the increase of control light field. Interestingly, a weak probe light beam can form spatial weak-light dark solitons. When it propagates along the axial direction, the soliton will transform into a steady spatial weak-light ring dark soltion. In addition, the stability of two-dimensional spatial optical solitons is testified numerically.

Quantum light source devices of In(Ga)As semiconductor self-assembled quantum dots

A brief introduction of semiconductor self-assembled quantum dots (QDs) applied in single-photon sources is given. Single QDs in confined quantum optical microcavity systems are reviewed along with their optical properties and coupling characteristics. Subsequently, the recent progresses in In(Ga)As QDs systems are summarized including the preparation of quantum light sources, multiple methods for embedding single QDs into different microcavities and the scalability of single-photon emitting wavelength. Particularly, several In(Ga)As QD single-photon devices are surveyed including In(Ga)As QDs coupling with nanowires, InAs QDs coupling with distributed Bragg reflection microcavity and the In(Ga)As QDs coupling with micropillar microcavities. Furthermore, applications in the field of single QDs technology are illustrated, such as the entangled photon emission by spontaneous parametric down conversion, the single-photon quantum storage, the chip preparation of single-photon sources as well as the single-photon resonance-fluorescence measurements.

SELF-ASSEMBLED QUANTUM DOTS ON AU AND THE INTERFACE FLUORESCENCE

In this paper,amino capped CdSe/ZnS quantum dots(QDs)were immobilized on the 11-mercaptoundecanoic acid(MUA)self-assembled Au surface(SAM/Au)by 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride(EDC).Atomic force microscopy(AFM),fluorescence imaging and electrochemistry were employed to characterize the surface.The results showed that CdSe/ZnS QDs were immobilized on the surface of SAM/Au successfully.Based on this method,the fluorescence of the QDs on the SAM/Au was monitored on-line.

Distribution of Ge Self-Assembled Quantum Dots on Six Ge1 - x Buffer Layers

The effect of buried misfit dislocation on the distribution of Ge self-assembled quantum dots (SAQDs) grown on a relaxed SiGe buffer layer was investigated. The strain field of arrays of buried dislocations in a relaxed SiGe buffer layer provided preferential nucleation sites for quantum dots. Burgers vector analysis using plan-view transmission electron microscopy (TEM) verified that the preferential nucleation sites of Ge SAQDs depended on the Burgers vector direction of corresponding dislocations. The measurement of the lateral distance between SAQDs and dislocations together with crosssection TEM observation clarified that the location of SAQDs was at the intersection of the dislocation slip plane and the top surface. The misfit strain should be an additional factor governing the uniformity in size, shape and distribution of Ge SAQDs.

Local Structure of Ge/Si(100) Self-Assembled Quantum Dots

Local structure of uncapped and Si capped Ge quantum dots grown on Si(100) has been probed by X ray absorption fine structure spectroscopy. It is found that the uncapped Ge dots are partially oxidized and partially alloyed with Si. The amount of Ge present in the Ge phase is found to be about 20 30%. In the Si capped sample, Ge is found to be dissolved in silicon, the fraction of Ge atoms existing as pure Ge phase being not more than 10%.

Threshold-independent method for single-shot readout of spin qubits in semiconductor quantum dots

The single-shot readout data process is essential for the realization of high-fidelity qubits and fault-tolerant quantum algorithms in semiconductor quantum dots. However, the fidelity and visibility of the readout process are sensitive to the choice of the thresholds and limited by the experimental hardware. By demonstrating the linear dependence between the measured spin state probabilities and readout visibilities along with dark counts, we describe an alternative threshold-independent method for the single-shot readout of spin qubits in semiconductor quantum dots. We can obtain the extrapolated spin state probabilities of the prepared probabilities of the excited spin state through the threshold-independent method. We then analyze the corresponding errors of the method, finding that errors of the extrapolated probabilities cannot be neglected with no constraints on the readout time and threshold voltage. Therefore, by limiting the readout time and threshold voltage, we ensure the accuracy of the extrapolated probability. We then prove that the efficiency and robustness of this method are 60 times larger than those of the most commonly used method. Moreover, we discuss the influence of the electron temperature on the effective area with a fixed external magnetic field and provide a preliminary demonstration for a single-shot readout of up to 0.7K/1.5T in the future.

Advantageous properties of halide perovskite quantum dots towards energy-efficient sustainable applications

As lead halide perovskite(LHP)semiconductors have shown tremendous promise in many application fields,and particularly made strong impact in the solar photovoltaic area,low dimensional quantum dot forms of these perovskites are showing the potential to make distinct marks in the fields of electronics,optoelectronics and photonics.The so-called perovskite quantum dots(PQDs)not only possess the most important features of LHP materials,i.e.,the unusual high defect tolerance,but also demonstrate clear quantum size effects,along with exhibiting desirable optoelectronic properties such as near perfect photoluminescent quantum yield,multiple exciton generation and slow hot-carrier cooling.Here,we review the advantageous properties of these nanoscale perovskites and survey the prospects for diverse applications which include lightemitting devices,solar cells,photocatalysts,lasers,detectors and memristors,emphasizing the distinct superiorities as well as the challenges.

Experimental and computational study of annealed nickel sulfide quantum dots for catalytic and antibacterial activity

This research investigates the hydrothermal synthesis and annealing duration effects on nickel sulfide(NiS_(2) quantum dots(QDs)for catalytic decolorization of methylene blue(MB)dye and antimicrobial efficacy.QD size increased with longer annealing,reducing catalytic activity.UV–vis,XRD,TEM,and FTIR analyses probed optical structural,morphological,and vibrational features.XRD confirmed NiS2's anorthic structure,with crystallite size growing from 6.53 to 7.81 nm during extended annealing.UV–Vis exhibited a bathochromic shift,reflecting reduced band gap energy(Eg)in NiS_(2).TEM revealed NiS_(2)QD formation,with agglomerated QD average size increasing from 7.13 to 9.65 nm with prolonged annealing.Pure NiS_(2) showed significant MB decolorization(89.85%)in acidic conditions.Annealed NiS_(2) QDs demonstrated notable antibacterial activity,yielding a 6.15mm inhibition zone against Escherichia coli(E.coli)compared to Ciprofloxacin.First-principles computation supported a robust interaction between MB and NiS_(2),evidenced by obtained adsorption energies.This study highlights the nuanced relationship between annealing duration,structural changes,and functional properties in NiS_(2)QDs,emphasizing their potential applications in catalysis and antibacterial interventions.

Coupling of BiOCl Ultrathin Nanosheets with Carbon Quantum Dots for Enhanced Photocatalytic Performance

Over the past few decades,photocatalysis technology has received extensive attention because of its potential to mitigate or solve energy and environmental pollution problems.Designing novel materials with outstanding photocatalytic activities has become a research hotspot in this field.In this study,we prepared a series of photocatalysts in which BiOCl nanosheets were modified with carbon quantum dots(CQDs)to form CQDs/BiOCl composites by using a simple solvothermal method.The photocatalytic performance of the resulting CQDs/BiOCl composite photocatalysts was assessed by rhodamine B and tetracycline degradation under visible-light irradiation.Compared with bare BiOCl,the photocatalytic activity of the CQDs/BiOCl composites was significantly enhanced,and the 5 wt%CQDs/BiOCl composite exhibited the highest photocatalytic activity with a degradation efficiency of 94.5%after 30 min of irradiation.Moreover,photocatalytic N_(2)reduction performance was significantly improved after introducing CQDs.The 5 wt%CQDs/BiOCl composite displayed the highest photocatalytic N_(2)reduction performance to yield NH_3(346.25μmol/(g h)),which is significantly higher than those of 3 wt%CQDs/BiOCl(256.04μmol/(g h)),7 wt%CQDs/BiOCl(254.07μmol/(g h)),and bare BiOCl(240.19μmol/(g h)).Our systematic characterizations revealed that the key role of CQDs in improving photocatalytic performance is due to their increased light harvesting capacity,remarkable electron transfer ability,and higher photocatalytic activity sites.

Effective Activation of Melamine for Synchronous Synthesis of Catalytically Active Nanosheets and Fluorescence-Responsive Quantum Dots

Because of the low reactivity of cyclic nitrides,liquid-phase synthesis of carbon nitride introduces challenges despite its favorable potential for energy-efficient preparation and superior applications.In this study,we demonstrate a strong interaction between citric acid and melamine through experimental observation and theoretical simulation,which eff ectively activates melamine-condensation activity and produces carbon-rich carbon nitride nanosheets(CCN NSs)during hydrothermal reaction.Under a large specific surface area and increased light absorption,these CCN NSs demonstrate significantly enhanced photocatalytic activity in CO_(2) reduction,increasing the CO production rate by approximately tenfold compared with hexagonal melamine(h-Me).Moreover,the product selectivity of CCN NSs reaches up to 93.5%to generate CO from CO_(2).Furthermore,the annealed CCN NSs exhibit a CO conversion rate of up to 95.30μmol/(g h),which indicates an 18-fold increase compared with traditional carbon nitride.During the CCN NS synthesis,nitrogen-doped carbon quantum dots(NDC QDs)are simultaneously produced and remain suspended in the supernatant after centrifugation.These QDs disperse well in water and exhibit excellent luminescent properties(QY=67.2%),allowing their application in the design of selective and sensitive sensors to detect pollutants such as pesticide 2,4-dichlorophenol with a detection limit of as low as 0.04μmol/L.Notably,the simultaneous synthesis of CCN NSs and NDC QDs provides a cost-eff ective and highly efficient process,yielding products with superior capabilities for catalytic conversion of CO_(2) and pollutant detection,respectively.

Temperature-controlled DCP Fluorescent Probe Based on Hydrogel-immobilized Quantum Dots Composite

A composite was created by incorporating the quantum dot-enhanced SiO_(2)nanoparticles within this hydrogel.Based on this composite,a temperature-controlled fluorescent probe for DCP was developed.A meticulous examination of this probe revealed its attributes and factors affecting its performance.By using temperature modulation,the probe was adept at detecting DCP concentrations ranging between 1.0×10^(-6)and 9.0×10^(-6)mol/L.Such a probe offers remarkable selectivity,repeatability,and robust stability,so that the detection of DCP can be carried out at different temperatures,and a fast,reliable,sensitive and low-cost intelligent detection method is realized.

Majorana tunneling in a one-dimensional wire with non-Hermitian double quantum dots

The combination of non-Hermitian physics and Majorana fermions can give rise to new effects in quantum transport systems. In this work, we investigate the interplay of PT-symmetric complex potentials, Majorana tunneling and interdot tunneling in a non-Hermitian double quantum dots system. It is found that in the weak-coupling regime the Majorana tunneling has pronounced effects on the transport properties of such a system, manifested as splitting of the single peak into three and a reduced 1/4 peak in the transmission function. In the presence of the PT-symmetric complex potentials and interdot tunneling, the 1/4 central peak is robust against them, while the two side peaks are tuned by them. The interdot tunneling only induces asymmetry, instead of moving the conductance peak, due to the robustness of the Majorana modes. There is an exceptional point induced by the union of Majorana tunneling and interdot tunneling. With increased PT-symmetric complex potentials, the two side peaks will move towards each other. When the exceptional point is passed through, these two side peaks will disappear. In the strong-coupling regime, the Majorana fermion induces a 1/4 conductance dip instead of the three-peak structure. PT-symmetric complex potentials induce two conductance dips pinned at the exceptional point. These effects should be accessible in experiments.

NbN quantum dots anchored hollow carbon nanorods as efficient polysulfide immobilizer and lithium stabilizer for Li-S full batteries

The shuttle effect of lithium polysulfides(LiPSs)and uncontrollable lithium dendrite growth seriously hinder the practical application of lithium-sulfur(Li-S)batteries.To simultaneously address such issues,monodispersed Nb N quantum dots anchored on nitrogen-doped hollow carbon nanorods(NbN@NHCR)are elaborately developed as efficient Li PSs immobilizer and Li stabilizer for high-performance Li-S full batteries.Density functional theory(DFT)calculations and experimental characterizations demonstrate that the sulfiphilic and lithiophilic NbN@NHCR hybrid can not only efficiently immobilize the soluble Li PSs and facilitate diffusion-conversion kinetics for alleviating the shuttling effect,but also homogenize the distribution of Li+ions and regulate uniform Li deposition for suppressing Li-dendrite growth.As a result,the assembled Li-S full batteries(NbN@NHCR-S||Nb N@NHCR-Li)deliver excellent long-term cycling stability with a low decay rate of 0.031%per cycle over 1000 cycles at high rate of 2 C.Even at a high S loading of 5.8 mg cm^(-2)and a low electrolyte/sulfur ratio of 5.2μL mg^(-1),a large areal capacity of 6.2 mA h cm^(-2)can be achieved in Li-S pouch cell at 0.1 C.This study provides a new perspective via designing a dual-functional sulfiphilic and lithiophilic hybrid to address serious issues of the shuttle effect of S cathode and dendrite growth of Li anode.

Small but mighty:Empowering sodium/potassium-ion battery performance with S-doped SnO_(2) quantum dots embedded in N,S codoped carbon fiber network

SnO_(2) has been extensively investigated as an anode material for sodium-ion batteries(SIBs)and potassium-ion batteries(PIBs)due to its high Na/K storage capacity,high abundance,and low toxicity.However,the sluggish reaction kinetics,low electronic conductivity,and large volume changes during charge and discharge hinder the practical applications of SnO_(2)-based electrodes for SIBs and PIBs.Engineering rational structures with fast charge/ion transfer and robust stability is important to overcoming these challenges.Herein,S-doped SnO_(2)(S-SnO_(2))quantum dots(QDs)(≈3 nm)encapsulated in an N,S codoped carbon fiber networks(S-SnO_(2)-CFN)are rationally fabricated using a sequential freeze-drying,calcination,and S-doping strategy.Experimental analysis and density functional theory calculations reveal that the integration of S-SnO_(2) QDs with N,S codoped carbon fiber network remarkably decreases the adsorption energies of Na/K atoms in the interlayer of SnO_(2)-CFN,and the S doping can increase the conductivity of SnO_(2),thereby enhancing the ion transfer kinetics.The synergistic interaction between S-SnO_(2) QDs and N,S codoped carbon fiber network results in a composite with fast Na+/K+storage and extraordinary long-term cyclability.Specifically,the S-SnO_(2)-CFN delivers high rate capacities of 141.0 mAh g^(−1) at 20 A g^(−1) in SIBs and 102.8 mAh g^(−1) at 10 A g^(−1) in PIBs.Impressively,it delivers ultra-stable sodium storage up to 10,000 cycles at 5 A g^(−1) and potassium storage up to 5000 cycles at 2 A g^(−1).This study provides insights into constructing metal oxide-based carbon fiber network structures for high-performance electrochemical energy storage and conversion devices.

Embedded high-quality ternary GaAs_(1−x)Sb_(x) quantum dots in GaAs nanowires by molecular-beam epitaxy

Semiconductor quantum dots are promising candidates for preparing high-performance single photon sources.A basic requirement for this application is realizing the controlled growth of high-quality semiconductor quantum dots.Here,we report the growth of embedded GaAs_(1−x)Sb_(x) quantum dots in GaAs nanowires by molecular-beam epitaxy.It is found that the size of the GaAs_(1−x)Sb_(x) quantum dot can be well-defined by the GaAs nanowire.Energy dispersive spectroscopy analyses show that the antimony content x can be up to 0.36 by tuning the growth temperature.All GaAs_(1−x)Sb_(x) quantum dots exhibit a pure zinc-blende phase.In addition,we have developed a new technology to grow GaAs passivation layers on the sidewalls of the GaAs_(1−x)Sb_(x) quantum dots.Different from the traditional growth process of the passivation layer,GaAs passivation layers can be grown simultaneously with the growth of the embedded GaAs_(1−x)Sb_(x) quantum dots.The spontaneous GaAs passivation layer shows a pure zinc-blende phase due to the strict epitaxial relationship between the quantum dot and the passivation layer.The successful fabrication of embedded high-quality GaAs_(1−x)Sb_(x) quantum dots lays the foundation for the realization of GaAs_(1−x)Sb_(x)-based single photon sources.

A highly sensitive ratiometric near-infrared nanosensor based on erbium-hyperdoped silicon quantum dots for iron(Ⅲ) detection

Ratiometric fluorescent detection of iron(Ⅲ)(Fe^(3+))offers inherent self-calibration and contactless analytic capabilities.However,realizing a dual-emission near-infrared(NIR)nanosensor with a low limit of detection(LOD)is rather challenging.In this work,we report the synthesis of water-dispersible erbium-hyperdoped silicon quantum dots(Si QDs:Er),which emit NIR light at the wavelengths of 810 and 1540 nm.A dual-emission NIR nanosensor based on water-dispersible Si QDs:Er enables ratiometric Fe^(3+)detection with a very low LOD(0.06μM).The effects of pH,recyclability,and the interplay between static and dynamic quenching mechanisms for Fe^(3+)detection have been systematically studied.In addition,we demonstrate that the nanosensor may be used to construct a sequential logic circuit with memory functions.

The binding energy of a hydrogenic impurity in self-assembled double quantum dots

The binding energy of a hydrogenic impurity in self-assembled double quantum dots is calculated via the finitedifference method. The variation in binding energy with donor position, structure parameters and external magnetic field is studied in detail. The results found are： （i） the binding energy has a complex behaviour due to coupling between the two dots; （ii） the binding energy is much larger when the donor is placed in the centre of one dot than in other positions; and （iii） the external magnetic field has different effects on the binding energy for different quantum-dot sizes or lateral confinements.

Magneto-optical properties of self-assembled InAs quantum dots for quantum information processing

Semiconductor quantum dots have been intensively investigated because of their fundamental role in solid-state quan- tum information processing. The energy levels of quantum dots are quantized and can be tuned by external field such as optical, electric, and magnetic field. In this review, we focus on the development of magneto-optical properties of single InAs quantum dots embedded in GaAs matrix, including charge injection, relaxation, tunneling, wavefunction distribution, and coupling between different dimensional materials. Finally, the perspective of coherent manipulation of quantum state of single self-assembled quantum dots by photocurrent spectroscopy with an applied magnetic field is discussed.

SURFACE MORPHOLOGY OF SELF-ASSEMBLED VERTICALLY STACKED InAs QUANTUM DOTS BY SIZE-CONTROLLED GROWTH

Structural and optical properties of vertically aligned InAs quantum dots (QDs) were embedded in Al0.5Ga0.5As spacer layers. The aligned QDs were grown at 520℃ in the Stranski-Krastanow (S-K) growth mode of molecular beam epitaxy. To impro ve QD characteristics, we employed a size- and density-controlled growth procedu re in the upper layers. Measurements by reflection high-energy electron diffract ion (RHEED) and atomic force microscopy (AFM) showed that both the size and dens ity of the QDs. The temperature dependence of the wavelength-integrated photolum inescence (PL) intensity revealed the InAs QD emission.

Computational Methods for Electromechanical Fields in Self-Assembled Quantum Dots

A detailed comparison of continuum and valence force field strain calculations in quantum-dot structures is presented with particular emphasis to boundary conditions,their implementation in the finite-elementmethod,and associated implications for electronic states.The first part of this work provides the equation framework for the elastic continuum model including piezoelectric effects in crystal structures as well as detailing the Keating model equations used in the atomistic valence force field calculations.Given the variety of possible structure shapes,a choice of pyramidal,spherical and cubic-dot shapes is made having in mind their pronounced shape differences and practical relevance.In this part boundary conditions are also considered;in particular the relevance of imposing different types of boundary conditions is highlighted and discussed.In the final part,quantum dots with inhomogeneous indium concentration profiles are studied in order to highlight the importance of taking into account the exact In concentration profile for real quantum dots.The influence of strain,electric-field distributions,and material inhomogeneity of spherical quantum dots on electronic wavefunctions is briefly discussed.