Multiple Quantum Dots Research Articles

Internal polarization electric field effects on the efficiency of InN/In[formula omitted]N multiple quantum dot solar cells

In this work, we investigate the influence of the internal electric field induced by the polarization inside the active region of the p-i-n photodiode on the characteristics of InN/InxGa1-xN quantum dots intermediate band solar cell. Considering the conduction and valence band offsets, the electron and hole energy levels have been determined by solving analytically the corresponding Schrödinger equations. The hole level, usually neglected in similar studies, is taken into account to determine all the intermediate transitions. All parameters of multiple quantum dot solar cells such as open-circuit voltage, short-circuit current density and photovoltaic conversion efficiency are determined as functions of the indium content, the internal electric field, inter-dot distances and dot sizes. Our calculations show that determining the photovoltaic conversion efficiency (η) without taking into account the internal electric field leads to an overestimation of η.

Spectral and temporal optical signal generation using randomly distributed quantum dots

Quantum dots (QDs) have a great potential for realizing information processing because of their signal-modulation capability based on energy transfer. We present a method for generating diverse temporal and spectral signals based on the energy transfer between multiple QDs. The method uses randomly distributed QDs, so it is not necessary to precisely arrange a QD network. With multiple energy transfers between QDs, a variety of signals within the QD network can be generated by optical inputs. Experimental results revealed that fluorescence decays of dense QDs were faster when the density of QDs or the irradiation intensity decreased. Furthermore, depending on the positions, stacked QDs showed different spectral responses. The randomly distributed QDs can generate diverse signals, which is essential for signal processing to handle temporal information.

Multiplexed detection of micro-RNAs based on microfluidic multi-color fluorescence droplets.

In this work, simple, rapid, and low-cost multiplexed detection of tumor-related micro-RNAs (miRNAs) was achieved based on multi-color fluorescence on a microfluidic droplet chip, which simplified the complexity of light path to a half. A four-T-junction structure was fabricated to form uniform nano-volume droplet arrays with customized contents. Multi-color quantum dots (QDs) used as the fluorescence labels were encapsulated into droplets to develop the multi-path fluorescence detection module. We designed an integrated multiplex fluorescence resonance energy transfer system assisted by multiple QDs (four colors) and one quencher to detect four tumor-related miRNAs (miRNA-20a, miRNA-21, miRNA-155, and miRNA-221). The qualitative analysis of miRNAs was realized by the color identification of QDs, while the quantitative detection of miRNAs was achieved based on the linear relationship between the quenching efficiency of QDs and the concentration of miRNAs. The practicability of the multiplex detection device was further confirmed by detecting four tumor-related miRNAs in real human serum samples. The detection limits of four miRNAs ranged from 35 to 39pmol/L was achieved without any target amplification. And the linear range was from 0.1nmol/L to 1μmol/L using 10nL detection volume (one droplet) under the detection speed of 320 droplets per minute. The multiple detection system for miRNAs is simple, fast, and low-cost and will be a powerful platform for clinical diagnostic analysis. Graphical abstract.

One, two, three, many.

A strain-tuning technique has been developed to interface multiple quantum dots within the same photonic chip.

Weyl points in systems of multiple semiconductor-superconductor quantum dots

As an analogy to the Weyl point in k-space, we search for energy levels which close at a single point as a function of a three dimensional parameter space. Such points are topologically protected in the sense that any perturbation which acts on the two level subsystem can be corrected by tuning the control parameters. We find that parameter controlled Weyl points are ubiquitous in semiconductor-superconductor quantum dots and that they are deeply related to Majorana zero modes. In this paper, we present several semiconductor-superconductor quantum dot devices which host parameter controlled Weyl points. Further, we show how these points can be observed experimentally via conductance measurements.

A Physiologically-Based Pharmacokinetic Model for Targeting Calcitriol-Conjugated Quantum Dots to Inflammatory Breast Cancer Cells.

Quantum dots (QDs) conjugated with 1,25 dihydroxyvitamin D3 (calcitriol) and Mucin‐1 (MUC‐1) antibodies (SM3) have been found to target inflammatory breast cancer (IBC) tumors and reduce proliferation, migration, and differentiation of these tumors in mice. A physiologically‐based pharmacokinetic model has been constructed and optimized to match experimental data for multiple QDs: control QDs, QDs conjugated with calcitriol, and QDs conjugated with both calcitriol and SM3 MUC1 antibodies. The model predicts continuous QD concentration for key tissues in mice distinguished by IBC stage (healthy, early‐stage, and late‐stage). Experimental and clinical efforts in QD treatment of IBC can be augmented by in silico simulations that predict the short‐term and long‐term behavior of QD treatment regimens.

Coherence and indistinguishability of highly pure single photons from non-resonantly and resonantly excited telecom C-band quantum dots

The role of resonant pumping schemes in improving the photon coherence is investigated on InAs/InGaAs/GaAs quantum dots (QDs) emitting in the telecom C-band. The linewidths of transitions of multiple exemplary quantum dots are determined under above-band pumping and resonance fluorescence (RF) via Fourier-transform spectroscopy and resonance scans, respectively. The average linewidth is reduced from (9.74 ± 3.3) GHz in the above-band excitation to (3.50 ± 0.39) GHz under RF underlining its superior coherence properties. Furthermore, the feasibility of coherent state preparation with a fidelity of (49.2 ± 5.8)% is demonstrated, constituting a first step toward on-demand generation of coherent, single, telecom C-band photons directly emitted by QDs. Finally, two-photon excitation of the biexciton is investigated as a resonant pumping scheme. A deconvoluted single-photon purity value of gHBT(2)(0)=0.072 ± 0.104 and a postselected degree of indistinguishability of VHOM=0.894 ± 0.109 are determined for the biexciton transition. This represents another step in demonstrating the necessary quantum optical properties for prospective applications.

Scalable in operando strain tuning in nanophotonic waveguides enabling three-quantum-dot superradiance.

The quest for an integrated quantum optics platform has motivated the field of semiconductor quantum dot research for two decades. Demonstrations of quantum light sources, single photon switches, transistors and spin-photon interfaces have become very advanced. Yet the fundamental problem that every quantum dot is different prevents integration and scaling beyond a few quantum dots. Here, we address this challenge by patterning strain via local phase transitions to selectively tune individual quantum dots that are embedded in a photonic architecture. The patterning is implemented with in operando laser crystallization of a thin HfO2 film 'sheath' on the surface of a GaAs waveguide. Using this approach, we tune InAs quantum dot emission energies over the full inhomogeneous distribution with a step size down to the homogeneous linewidth and a spatial resolution better than 1 µm. Using these capabilities, we tune multiple quantum dots into resonance within the same waveguide and demonstrate a quantum interaction via superradiant emission from three quantum dots.

Fast raster scan multiplexed charge stability measurements toward high-throughput quantum dot array calibration

We report raster scan multiplexed charge-stability diagram measurements for tuning multiple gate-defined quantum dots in GaAs/AlGaAs heterostructures. We evaluate the charge sensitivity of the quantum point contact (QPC) in both radio frequency (rf)-reflectometry and direct current-transport modes, where we measure the signal-to-noise ratio (SNR) of 40 for rf-QPC with an integration time per pixel of 10 ms, corresponding to 1.14 ms for resolving single electron transition in the few electron regime. The high SNR for reasonable integration time allows fast two-dimensional (2D) scanning, which we use to facilitate double and triple quantum dot (TQD) tuning processes. We configure a highly stable raster scan multiplexed quantum dot tuning platform using a switching matrix and transformer-coupled alternating current ramp sources with software control. As an example of high-throughput multiple quantum dot tuning, we demonstrate systematic TQD formation using this platform in which a multiplexed combination of 2D scans enables the identification of the few electron regime in multiple quantum dots in just a few minutes. The method presented here is general, and we expect that the tuning platform is applicable to more complex multiple quantum dot arrays, allowing efficient quantum dot system Hamiltonian parameter calibration.

On the formation of multiple quantum dots inside elongated pits on semiconductor films deposited epitaxially on pit-patterned substrates

We report numerical simulation results that provide a comprehensive explanation to recent experimental observations of multiple quantum dot formation inside pits on surfaces of thin films grown epitaxially on nanofabricated substrates with ordered patterns of pits that are elongated and have unequal pit wall inclinations. Our self-consistent dynamical simulations are based on a properly parameterized surface morphological evolution model for biaxially stressed epitaxial thin films and are supported by a nonlinear surface morphological stability theory. Consistently with the experimental observations, we find that quantum dots form inside pits on the film surface if the pits are sufficiently large, with sufficiently steep pit wall slopes, and that the number of quantum dots forming inside each one of these pits increases with increasing length of the long side of elongated pits with different wall inclinations along the two principal pit directions. We also demonstrate that we can precisely control how many quantum dots will form inside each one of the pits by properly tailoring geometrical parameters of the pits on the substrate, such as the pit opening dimensions and pit wall slopes.

(Invited) Multifunctional Nanoplatforms for Biomedical Applications

Near-infrared (NIR) absorbing and emitting nanomaterials attract significant attention in bioimaging, which shows great potential for disease detection due to its high sensitivity at the subcellular level and low cost of related imaging facilities. However, currently available optical probes are mainly based on visible-emitting materials. The tissue-induced optical extinction and autofluorescence in the visible range result in limited penetration depth and ambiguous photoluminescence signal, which restricts their in vivo use. To address this issue, photoluminescent probes, with both absorption and emission wavelengths operating in the biological windows in the NIR range, in which tissues are optically transparent, are highly desired. Their integration with superparamagnetic nanomaterials to make a multifunctional platform further opens a wide range of promising applications, including bimodal imaging (photoluminescence and magnetic resonance imaging), synergistic hyperthermia (magnetothermal and photothermal), magnetic confinement of trace amounts of biospecies for ultra high-sensitivity biodetection, etc. In this talk, I will present our most recent work on the synthesis of NIR-emitting water soluble, stable core/shell/shell quantum dots (QDs) and multifunctional (NIR photoluminescent and superparamagnetic) nanoparticles and their use in biomedicine. For instance, in one case, multifunctional particles contain single superparamagnetic nanoparticles as cores and NIR-luminescent nanomaterials as shells. In another case, the multifunctional nanoplatform is compose of multiple superparamagnetic nanoparticles and NIR quantum dots in single particles. These different types of multifunctional particles are designed for different biomedical applications.

Quantum dots-based chemiluminescence probes: an overview.

This mini-review describes the recent developments in quantum dots-based nanoprobes in liquid-phase chemiluminescence (CL) analysis. In the referenced reports, multiple quantum dots (QDs) were adopted as final emission species either after direct oxidation reactions (direct CL) or after chemiluminescence resonance energy transfer (indirect CL). This review does not include papers in which QDs have been used as enhancers, catalysts, carriers or quenchers in chemiluminescence systems. A brief overview on the CL mechanisms of various QDs-based nanoprobes and their analytical applications over the last decade is given, followed by comments on the future challenges and prospects in this field.

Nanoscale Patterning of Colloidal Nanocrystal Films for Nanophotonic Applications Using Direct Write Electron Beam Lithography.

The small size of colloidal nanocrystal quantum dots (QDs) leads to a variety of unique optical properties that are well-suited to nanophotonics, including bright, tunable photoluminescence (PL). However, exploring the properties of solid QD assemblies at the nanoscale has proven challenging because of the limitations in the nanoscale QD patterning methods. Generally, the precise placement of QD solids is difficult to achieve, especially for tall structures with multiple QD layers, and when it is achieved the patterns often cannot withstand the further processing steps required for final device construction. Direct electron beam lithography of QDs has emerged as a straightforward patterning process that does not require ligand exchange and results in structures that retain bright PL. Here, we demonstrate that direct patterning QD films on substrates treated with a self-assembled monolayer of octadecyltrichlorosilane allows us to create feature sizes as thin as 30 nm with heights of multiple layers and characterize the pattern resolution, robustness, and placement accuracy. These structures withstand sonication in a variety of solvents, and the structures are placed within 20 nm of their intended location nearly 100% of the time. We further show how this patterning method can be applied to nanophotonics by measuring the complex refractive index of the QD materials to model the absorption and scattering cross sections of QD structures of various sizes and shapes. These simulations reveal that edge effects arising from the finite shape of the QD nanostructure lead to substantial absorption enhancement when compared to an equivalent volume region taken from a continuous QD film. Finally, we explore more complex structures by patterning QD arrays, multilayer QD structures, and QD disks inside plasmonic resonators.

Electric field control of superexchange in multiple linear two-electron quantum dot arrays and mixed-valence molecules

This paper belongs to the area of electrical manipulation of spins in quantum dots and molecular spins for quantum technologies. We propose a theoretical analysis of the electric field controllable superexchange in the two-electron linear arrays of quantum dots (“physical” molecules) and linear mixed-valence molecules based on metal ions in different oxidation degrees (“chemical” molecules) of increasing length. In this view, we consider the kinetic magnetic exchange in trimeric and tetrameric linear arrays of quantum dots and the field dependence of the exchange interaction between electrons. An attainable electric field in these systems is able to essentially change the electronic distribution in the systems under consideration and subsequently to affect the exchange interaction. The numerical estimations demonstrate the feasibility of the revealed effects of the electric field. At a weak electric field, this control is shown to be more efficient for larger numbers of diamagnetic quantum dots mediating superexchange. The peculiarities of chemical analogs of such quantum dot arrays represented by the linear triferrocenium and tetraferrocenium complexes containing two mobile holes are discussed as well.

Comparison between InP-based quantum dot lasers with and without tunnel injection quantum well and the impact of rapid thermal annealing

An InP based tunnel injection quantum dot (QD) laser and a reference quantum dot laser designed to emit at 1.55 μm were grown by molecular beam epitaxy. The lattice matched tunnel injection (TI) structures consist of an InGaAs quantum well (QW), an InAlGaAs barrier and multiple InAs quantum dot layers. Quantum well and quantum dot test structures as well as the actual laser structures were treated with rapid thermal annealing (RTA) at varying temperatures (680–780 °C). Photoluminescence measurements were performed at 10 K on all samples and a strong effect of this annealing process on the emission properties is observed. The laser structures were processed into broad area lasers. Power-current characteristics were measured and evaluated. A strong improvement in device performance is observed after annealing for QD lasers while for TI-QD lasers no significant improvement was obtained, which might be caused by detuning of band energy alignment and different impact of the RTA process on the material quality of QW and QD layers.

Enhancing Third- and Fifth-Order Nonlinearity via Tunneling in Multiple Quantum Dots.

The nonlinearity of semiconductor quantum dots under the condition of low light levels has many important applications. In this study, linear absorption, self-Kerr nonlinearity, fifth-order nonlinearity and cross-Kerr nonlinearity of multiple quantum dots, which are coupled by multiple tunneling, are investigated by using the probability amplitude method. It is found that the linear and nonlinear properties of multiple quantum dots can be modified by the tunneling intensity and energy splitting of the system. Most importantly, it is possible to realize enhanced self-Kerr nonlinearity, fifth-order nonlinearity and cross-Kerr nonlinearity with low linear absorption by choosing suitable parameters for the multiple quantum dots. These results have many potential applications in nonlinear optics and quantum information devices using semiconductor quantum dots.

Electrode-induced lattice distortions in GaAs multi-quantum-dot arrays

Abstract

Visible-Light-Induced Nanoparticle Assembly for Effective Hydrogen Photogeneration

Visible-light-induced nanoparticle assembly consisting of quantum dots (QDs) and Pt nanoparticles (NPs) has been achieved. The assembled nanoparticle joined a single Pt nanoparticle and multiple QDs together through controllable oxidation of thiol ligands on QDs under aerobic visible light irradiation and sonication. With an optimal ratio of QDs to Pt NPs (ca. 475:1), the assembly could achieve consecutive electron transfer from photoexcited QDs to Pt NP and evolve H2 gas with a constant rate of ∼13.9 μmol h–1 from triethylamine (TEA) during 70 h, corresponding to a turnover number (TON) of 1.4 × 107 mol H2 per mol Pt NPs. Our work shows that the assembled architecture of semiconducting QDs is a promising strategy for effective and durable H2 photogeneration.

Green synthesized multiple fluorescent nitrogen-doped carbon quantum dots as an efficient label-free optical nanoprobe for in vivo live-cell imaging

In this work, nitrogen-doped carbon quantum dots (N-CQDs) have been synthesized successfully by a simple hydrothermal method and demonstrated its application for multicolor imaging in Caenorhabditis elegans (C. elegans) as an in vivo model. The synthesized N-CQDs were characterized by various physicochemical techniques such as XRD, Raman spectroscopy, ATR-FTIR spectroscopy, XPS, HRTEM, UV–vis spectroscopy, and fluorescence spectroscopy. The synthesized N-CQDs exhibited a strong fluorescence due to the uniform size distribution with nitrogen-containing and oxygen-containing functional groups onto the surface of N-CQDs which induce the excellent dispersibility in aqueous media. The N-CQDs has an excitation-dependent fluorescence behavior and the strongest fluorescence appeared at 411 nm (emission peak position) under the excitation of 340 nm. Also, the N-CQDs displayed a high quantum yield (QY) of 12.5. The fluorescence behaviour of the aqueous N-CQDs suspension retains for a long time up to 1 year. The prolonging fluorescent N-CQDs was utilized as a staining agent for bioimaging and toxicity of N-CQDs on C. elegans that was conducted by killing assay. In-vivo studies suggested that the N-CQDs displayed excellent biocompatibility and successfully used for high-contrast imaging of N-CQDs in living and dead C. elegans. Based on the strongest fluorescence along with excellent aqueous dispersibility and biocompatibility, the green synthesized N-CQDs would be an ideal candidate for many biological applications.

Colloidal Quantum Dot Arrangement Assisted by Perylene Bisimide Self-Assembly.

Colloidal semiconductor nanocrystals, so-called quantum dots (QDs), are attractive as molecular-like smart nanomaterials, and their emission and optoelectronic properties in the dispersed state have been actively studied. The construction of supramolecular structures composed of multiple QDs, however, is still challenging. Here, a new strategy to form supramolecular QD structures via self-assembly of perylene bisimide (PBI) dyes is demonstrated. In a mixed solution, QDs and PBI undergo time-dependent fusion to form an isolated colloidal QD-PBI complex or a unique QD-PBI co-aggregate composed of QDs arranged along a sheet-like PBI nanostructure, and these dramatically different supramolecular structures can be controlled by the solvent polarity.