Characterization Of Quantum Dots Research Articles

One-pot, easy and scalable synthesis of large-size short wave length IR emitting PbS quantum dots.

This study presents a versatile and efficient method to synthesize large-size lead sulfide (PbS) quantum dots (QDs) that display emission in the short-wave infrared (SWIR) region, using accessible and stable diethylammonium diethyldithiocarbamate (C2)2DTCA and octylammonium octyldithiocarbamate (C8DTCA) as sulfur sources. As these sulfur sources enable the formation of well-dispersed, large-size PbS QDs in a very convenient way, this method can further be taken up for scale-up studies. Importantly, this approach allows precise control over QD sizes, thereby enhancing their SWIR optical properties. By adjusting the hot injection temperatures and sulfur source concentrations, different synthesis routes are explored, providing flexibility for the desired QD characteristics. The results presented here offer a promising opportunity to leverage the synthesized PbS QDs in applications such as optoelectronics, sensors, and imaging technology.

Atomic-Scale Multimodal Characterization of Self-Assembled InAs/InGaAlAs Quantum Dots.

Self-assembled quantum dots (QDs) are potential candidates for photoelectric and photovoltaic devices, because of their discrete energy levels. The characterization of QDs at the atomic level using a multimodal approach is crucial to improving device performance because QDs are nanostructures with highly correlated structural parameters. In this study, scanning transmission electron microscopy, geometric phase analysis, and atom probe tomography were employed to characterize structural parameters such as the shape, strain, and composition of self-assembled InAs-QDs with InGaAlAs spacer layers. The measurements revealed characteristic AlAs-rich regions above the QDs and InAs-rich regions surrounding the QD columns, which can be explained by the relationship between the effect of strain and surface curvature around the QD. The methodology described in this study accelerates the development of future QD devices because its multiple perspectives reveal phenomena such as atomic-scale segregations and allow for more detailed discussions of the mechanisms of these phenomena.

Colloidal one-pot synthesis and characterization of Glycine capped Al(x) doped ZnS QDs for efficient UV light assisted photo-degradation of Stilbene 420 dye

In thisstudy, successful synthesis and characterization of undoped and Al-doped ZnS quantum dots (QDs) capped with bio-friendly glycine (ZnSAl/Gly) are described. The synthesis is accomplished through a one-pot colloidal co-precipitation process, followed by the characterization of QDs using various analytical techniques.X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HR-TEM) showed the formation of cubic-faced ZnS QDs, with the crystal size decreasing as the amount of Al doping increased. A ZnS phase layer on the QDs surface was also demonstrated by Fourier-transform infrared spectroscopy (FTIR) measurements. Field emission scanning electron microscopy with energy dispersive X-ray spectroscopy (FESEM-EDS) analysis was employed to examine the stoichiometry and shape of the synthesized QDs. Thermogravimetric analysis (TGA) showed a remarkable stability of Al-doped ZnS QDs over an extended period, enhancing their potential for a variety of applications. Measurements of the absorption band edge in the UV–Visible range demonstrated that Al ions were successfully incorporated into the ZnS lattice, causing a substantial red shift. This change, which caused the energy band gap to rise from 3.2 eV (ZnS/Gly) to 4.42 eV (ZnSAl1%/Gly), was attributed to the size confinement effect. The degradation of the Stilbene-420 dye under UV irradiation served as a test for the photodegradation capability of the synthesized QDs. The photodegradation efficiency of Al doping ranged from 60 % to 92 %, showing the induction of a significant number of crystalline structures with rising Al concentration. The Al-doped ZnS/Gly QDs are highly catalytic and photoactive, and they show great promise in the field of photoluminescence, medical and biological areas. Their potential for use as effective catalysts in waste water treatment methods is also remarkable.

Improving efficiency of silicon solar cells by integrating SiO2-coated lead-free Cs3Bi2Br9 perovskites quantum dots as luminescence down-shifting layer

Lead-based perovskite quantum dots (QDs) have promising applications in optoelectronic devices, but commercial applications are limited by the potential toxicity and poor stability of lead. Meanwhile, there are lattice, polarity, and thermal expansion coefficient mismatches in integrating semiconductor materials onto the surface of photoelectronic circuit devices, resulting in high-density defects limiting the reliability of photoelectronic devices. Therefore, there is a need to investigate perovskite alternatives that are non-toxic, stable, and can be effectively coupled to silicon photonic circuits. In this paper, lead-free perovskite Cs3Bi2Br9/SiO2 QDs were synthesized. The emission wavelength falls within the 400–560 nm range, exhibiting vibrant blue photoluminescence and demonstrating exceptional air stability for a duration exceeding 60 days. Optical tests and density-functional theory (DFT) calculations show that the silica shell layer effectively binds the electron and hole wave functions, prevents photon-generated carriers from escaping, reduces surface defects, and improves the carrier recombination probability. Meanwhile, using Cs3Bi2Br9/SiO2 QDs as a luminescent down-shifting (LDS) layer in combination with a conventional silicon solar cell, the photovoltaic conversion power was increased by 1.82%. Hence, the core-shell structure is designed by the green environmental protection method to control the improvement of the PL characteristics of QDs, which opens a window for the synthesis of new barrier materials in ethanol and water systems, making the Cs3Bi2Br9/SiO2 QDs have great potential for the application of novel optoelectronic devices in the future.

Development of a biomimetic DNA delivery system by encapsulating polyethyleneimine functionalized silicon quantum dots with cell membranes.

Quantum dots (QDs) are renowned for their remarkable optoelectronic properties, making them suitable for applications such as bioimaging and optoelectronics. However, their use in gene delivery has been restricted due to the low DNA loading capacity. This study aimed to develop a biomimetic DNA delivery system by encapsulating polyethyleneimine (PEI) functionalized silicon QDs (SiQDs) with cell membranes and evaluate its potential as a gene vector in vitro. To achieve this, hydrophilic dispersed silicon QDs (PQDs) were prepared through a one-pot hydrothermal reaction of PEI and 3-Aminopropyltrimethoxysilane (APTMS). Subsequently, red blood cell membrane (RBCM) encapsulated biomimetic QDs (CM-PQDs) was obtained through the extrusion method. The CM-PQDs exhibited higher DNA loading capacity and better stability than naked SiQDs. The CM-PQDs/DNA complex was effectively taken up by cells, as observed through the fluorescence characteristics of QDs themselves. Both CM-P10QDs (prepared with PEI10k) and CM-P25QDs (prepared with PEI25k) could deliver DNA into cells and express the reporter protein successfully. CM-P25QDs showed a higher transfection efficiency of 77.32% in 293T cells and 47.11% in HeLa cells than SiQDs and CM-P10QDs. The results also indicated that cell membrane encapsulation could effectively reduce the cytotoxicity of SiQDs further. Therefore, the study concludes that CM-PQDs have the potential to serve as a safe and traceable biomimetic gene delivery system.

Digital holographic nanoscopy for erythrocyte, nanoparticle and quantum dot characterization

Optical detection of biological cells and nanoparticles is a challenging task in optical physics due to the individual nanoparticles' low inherent scattering, size, and shape. High magnification is required for the study of such particles. In the present work, we have introduced a modified Digital Holographic Microscopy (DHM) for qualitative and quantitative optical characterization of biological cells, nanoparticles and quantum dots through phase measurement. The proposed system can measure a quantum dot of a minimum size of 6.8 nanometers with 1,53,284X magnification by placing two Microscope Objective (MO) lenses in the path of the object beam of the DHM. We have recorded digital holograms of the specimen for different combinations of MOs by varying distances between them. The system can characterize the specimen of micro to nanometer scales by varying its magnification as per requirements. The results are shown for human erythrocytes of diameter of 7.31 ± 0.08 µm & thickness of 2.3 ± 0.058 µm and gold nanoparticles (AuNPs) of different sizes (6.8 nm - 50 nm). The size of erythrocytes and AuNPs are determined experimentally using the DHM by mapping with USAF-1951 high-resolution microscope targets. The obtained results are verified by Field Emission Scanning Electron Microscopy (FESEM) and High-Resolution Transmission Electron Microscopy (HRTEM) measurements.

Optically asymmetric down-shifting films for highly efficient photovoltaics

Quantum dots (QDs) have been regarded as promising spectral converters for photovoltaic (PV) devices owing to their excellent photoluminescence (PL) characteristics. Herein, we report a highly-efficient QD hierarchical (QD-Hie) film that elevates the PV performance by integrating QDs with micro/nano hierarchical structures. The proposed film was designed to ensure low reflectance for incident light (air-to-device) and high reflectance for escape light (device-to-air), obtaining a light-trapping effect to increase the absorption of PVs at wide incident angles. The trapped ultraviolet photons in our film promoted the downshifting property of the QDs and amplified the generation of visible photons, thereby enhancing the PL characteristics of QDs up to 3.71 times with independency of the incidence angle. Furthermore, the hierarchical structure restricts the outward release of converted QDPL, ensuring high availability of the down-shifted photons to PVs. The optical benefit of our film was maximized by attaching them on both sides of bifacial semi-transparent dye-sensitized solar cells, resulting in the short-circuit current density (JSC) improvement of up to 25.97% under AM 1.5G illumination. Along with its high versatility and outstanding JSC increments, our study presents a new perspective of advanced spectral converting layers and provides practical viability for various optoelectronic devices.

Patternable quantum dot color conversion film based on photolithography technique

This paper presents a patternable two-color quantum dot (QD) color conversion film based on photolithography technique. Toluene-assisted dispersion of QD powder with the best performance matching was selected from four typical dispersions by experimental comparison. On this basis, the color conversion film of QD was prepared by photolithography technique. The experimental results show that the height of the patternable QD microstructures has good consistency. At the same time, the monochromatic spectrum test shows that the spectral characteristics of QDs are not significantly affected by the photolithographic process. Therefore, the preparation methods described in this paper can provide a reference for related research.

Quantum Dot-Peptide Conjugates as Energy Transfer Probes for Sensing the Proteolytic Activity of Matrix Metalloproteinase-14.

We detail the assembly and characterization of quantum dot (QD)-dye conjugates constructed using a peptide bridge specifically designed to recognize and interact with a breast cancer biomarker─matrix metalloproteinase-14 (MMP-14). The assembled QD conjugates are then used as optically addressable probes, relying on Förster resonance energy transfer (FRET) interactions as a transduction mechanism to detect the activity of MMP-14 in solution phase. The QDs were first coated with dithiolane poly(ethylene glycol) (PEG) bearing a carboxyl group that allows coupling via amide bond formation with different dye-labeled peptides. The analytical capability of the conjugates is enabled by correlating changes in the FRET efficiency with the conjugate valence and/or QD-to-dye separation distance, triggered and modulated by enzymatic proteolysis of surface-tethered peptides. The FRET probe exhibits great sensitivity to enzyme digestion with sub-nanomolar limit of detection. We further analyze the proteolysis data within the framework of the Michaelis-Menten model, which considers the fact that surface-attached peptides have a slower diffusion coefficient than free peptides. This results in reduced collision frequency and lower catalytic efficiency, kcat/KM. Our results suggest that our conjugate design is promising, effective, and potentially useful for in vivo analysis.

Progression of Quantum Dots Confined Polymeric Systems for Sensorics.

The substantial fluorescence (FL) capabilities, exceptional photophysical qualities, and long-term colloidal stability of quantum dots (QDs) have aroused a lot of interest in recent years. QDs have strong and wide optical absorption, good chemical stability, quick transfer characteristics, and facile customization. Adding polymeric materials to QDs improves their effectiveness. QDs/polymer hybrids have implications in sensors, photonics, transistors, pharmaceutical transport, and other domains. There are a great number of review articles available online discussing the creation of CDs and their many uses. There are certain review papers that can be found online that describe the creation of composites as well as their many different uses. For QDs/polymer hybrids, the emission spectra were nearly equal to those of QDs, indicating that the optical characteristics of QDs were substantially preserved. They performed well as biochemical and biophysical detectors/sensors for a variety of targets because of their FL quenching efficacy. This article concludes by discussing the difficulties that still need to be overcome as well as the outlook for the future of QDs/polymer hybrids.

Single-electron pump in a quantum dot array for silicon quantum computers

It is necessary to load single electrons into individual quantum dots (QDs) in an array for implementing fully scalable silicon-based quantum computers. However, this single-electron loading would be impacted by the variability of the QD characteristics, and suppressing this variability is highly challenging even in the state-of-the-art silicon front-end process. Here, we used a single-electron pump (SEP) for loading single electrons into a QD array as a preparatory step to use electrons as spin qubits. We used parallel gates in the QD array as a SEP and demonstrated 100 MHz operation with an accuracy of 99% at 4 K. By controlling the timing of a subsequent gate synchronously as a shutter, we found that the jitter representing electron transfer was less than 10 ns, which would be acceptable for a typical operating speed of around 1 MHz for silicon qubits.

Recent trends in macromolecule-conjugated hybrid quantum dots for cancer theranostic applications.

Quantum dots (QDs) are small nanoparticles with semiconductor properties ranging from 2 to 10 nanometers comprising 10-50 atoms. The single wavelength excitation character of QDs makes it more significant, as it can excite multiple particles in a confined surface simultaneously by narrow emission. QDs are more photostable than traditional organic dyes; however, when injected into tissues, whole animals, or ionic solutions, there is a significant loss of fluorescence. HQD-based probes conjugated with cancer-specific ligands, antibodies, or peptides are used in clinical diagnosis. It is more precise and reliable than standard immunohistochemistry (IHC) at minimal protein expression levels. Advanced clinical studies use photodynamic therapy (PDT) with fluorescence imaging to effectively identify and treat cancer. Recent studies revealed that a combination of unique characteristics of QDs, including their fluorescence capacity and abnormal expression of miRNA in cancer cells, were used for the detection and monitoring progression of cancer. In this review, we have highlighted the unique properties of QDs and the theranostic behavior of various macromolecule-conjugated HQDs leading to cancer treatment.

Quantum Mechanical Analysis Based on Perturbation Theory of CdSe/ZnS Quantum-Dot Light-Emission Properties.

A simulation of quantum dot (QD) energy levels was designed to reproduce a quantum mechanical analytic method based on perturbation theory. A Schrödinger equation describing an electron–hole pair in a QD was solved, in consideration of the heterogeneity of the material parameters of the core and shell. The equation was solved numerically using single-particle basis sets to obtain the eigenstates and energies. This approach reproduced an analytic solution based on perturbation theory, while the calculation was performed using a numerical method. Owing to the effectiveness of the method, QD behavior according to the core diameter and external electric field intensity could be investigated reliably and easily. A 9.2 nm diameter CdSe/ZnS QD with a 4.2 nm diameter core and 2.5 nm thick shell emitted a 530 nm green light, according to an analysis of the effects of core diameter on energy levels. A 4 nm redshift at V/cm electric field intensity was found while investigating the effects of external electric field on energy levels. These values agree well with previously reported experimental results. In addition to the energy levels and light emission wavelengths, the spatial distributions of wavefunctions were obtained. This analysis method is widely applicable for studying QD characteristics with varying structure and material compositions and should aid the development of high-performance QD technologies.

Nondestructive Photopatterning of Heavy‐Metal‐Free Quantum Dots

Electroluminescence from quantum dots (QDs) is a suitable photon source for futuristic displays offering hyper-realistic images with free-form factors. Accordingly, a nondestructive and scalable process capable of rendering multicolored QD patterns on a scale of several micrometers needs to be established. Here, nondestructive direct photopatterning for heavy-metal-free QDs is reported using branched light-driven ligand crosslinkers (LiXers) containing multiple azide units. The branched LiXers effectively interlock QD films via photo-crosslinking native aliphatic QD surface ligands without compromising the intrinsic optoelectronic properties of QDs. Using branched LiXers with six sterically engineered azide units, RGB QD patterns are achieved on the micrometer scale. The photo-crosslinking process does not affect the photoluminescence and electroluminescence characteristics of QDs and extends the device lifetime. This nondestructive method can be readily adapted to industrial processes and make an immediate impact on display technologies, as it uses widely available photolithography facilities and high-quality heavy-metal-free QDs with aliphatic ligands.

Study of Size, Shape, and Etch pit formation in InAs/InP Droplet Epitaxy Quantum Dots

We investigated metal-organic vapor phase epitaxy grown droplet epitaxy (DE) and Stranski–Krastanov (SK) InAs/InP quantum dots (QDs) by cross-sectional scanning tunneling microscopy (X-STM). We present an atomic-scale comparison of structural characteristics of QDs grown by both growth methods proving that the DE yields more uniform and shape-symmetric QDs. Both DE and SKQDs are found to be truncated pyramid-shaped with a large and sharp top facet. We report the formation of localized etch pits for the first time in InAs/InP DEQDs with atomic resolution. We discuss the droplet etching mechanism in detail to understand the formation of etch pits underneath the DEQDs. A summary of the effect of etch pit size and position on fine structure splitting (FSS) is provided via the k · p theory. Finite element (FE) simulations are performed to fit the experimental outward relaxation and lattice constant profiles of the cleaved QDs. The composition of QDs is estimated to be pure InAs obtained by combining both FE simulations and X-STM results. The preferential formation of {136} and {122} side facets was observed for the DEQDs. The formation of a DE wetting layer from As-P surface exchange is compared with the standard SKQDs wetting layer. The detailed structural characterization performed in this work provides valuable feedback for further growth optimization to obtain QDs with even lower FSS for applications in quantum technology.

Quantum Dots for Cancer-Related miRNA Monitoring.

Quantum dots (QDs) possess exceptional optoelectronic properties that enable their use in the most diverse applications, namely, in the medical field. The prevalence of cancer has increased and has been considered the major cause of death worldwide. Thus, there has been a great demand for new methodologies for diagnosing and monitoring cancer in cells to provide an earlier prognosis of the disease and contribute to the effectiveness of treatment. Several molecules in the human body can be considered relevant as cancer markers. Studies published over recent years have revealed that micro ribonucleic acids (miRNAs) play a crucial role in this pathology, since they are responsible for some physiological processes of the cell cycle and, most important, they are overexpressed in cancer cells. Thus, the analytical sensing of miRNA has gained importance to provide monitoring during cancer treatment, allowing the evaluation of the disease's evolution. Recent methodologies based on nanochemistry use fluorescent quantum dots for sensing of the miRNA. Combining the unique characteristics of QDs, namely, their fluorescence capacity, and the fact that miRNA presents an aberrant expression in cancer cells, the researchers created diverse strategies for miRNA monitoring. This review aims to present an overview of the recent use of QDs as biosensors in miRNA detection, also highlighting some tutorial descriptions of the synthesis methods of QDs, possible surface modification, and functionalization approaches.

Direct detection of electronic states for individual indium arsenide (InAs) quantum dots grown by molecular beam epitaxy

Indium arsenide (InAs) quantum dots (QDs) have been characterized using a conductive-mode atomic force microscope (C-AFM), where a well-defined gold-coated AFM probe has been used to electrically probe each individual QD. The InAs QDs were grown on a gallium arsenide (GaAs) substrate in a self-assembled manner by using molecular beam epitaxy (MBE). The measured current-voltage (I-V) curves of individual QDs exhibit a typical Schottky diode behavior, which can be attributed to the metal/semiconductor junction between the AFM gold probe and the n-doped GaAs bulk. However, distinct I-V curves are observed in sequential measurements, where a less forward turn-on voltage is measured in the subsequent voltage sweeps compared to the initial sweep. However, this effect is not evident when the same measurements are conducted on a plane surface (in the absence of QDs) on the same substrate. The discrete voltage values at the forward bias on a QD indicates a change in the electronic states due to trapped electrons in the QD during the initial voltage sweep. These unique characteristics of QDs can be exploited for potential applications in fast-response data storage devices and quantum computing.

The Preparation and Characterization of Quantum Dots in Polysaccharide Carriers (Starch/Chitosan) as Elements of Smart Packaging and Their Impact on the Growth of Microorganisms in Food.

Nanocomposite materials are increasingly commonly used to ensure food safety and quality. Thanks to their unique properties, stemming from the presence of nanoparticles, they are used to develop advanced sensors and biosensors, e.g., for various harmful substances, heavy metals, microorganism growth, and environmental changes in food products. The aim of this study is to produce novel films based on natural resources—potato starch and chitosan—incorporating generated quantum dots of zinc sulfide and cadmium sulfide. The biocomposites were subjected to the following assays: FTIR spectroscopy, UV-VIS spectroscopy, photoluminescence spectroscopy, and SEM/TEM spectroscopy. Their mechanical properties were also analyzed, a colorimetric analysis was performed, and the water content, solubility, and water absorption capacity were determined. A storage test was also performed, using poultry meat covered with the produced films, to assess the microbiological quality. The results confirmed the presence of the quantum dots in the starch–chitosan matrix. The unique optical properties of the films were also demonstrated. It was shown that the composites with nanoparticles limited the growth of selected microorganisms in poultry meat. The food storage time was found to have an impact on the fluorescent properties of the composites. The results point to the possibility of using the produced films as active and smart packaging.

Hybrid cube-in-cup nanoantenna: towards ordered photonics

The most significant goal of nanophotonics is the development of high-speed quantum emitting devices operating at ambient temperature. In this regard, plasmonic nanoparticles-on-mirror are potential candidates for designing high-speed photon sources. We introduce a novel hybrid nanoantenna (HNA) with CdSe/CdS colloidal quantum dots (QDs) based on a silver nanocube in a metal cup that presents a nanoparticle-in-cavity coupled with an emitters system. We use focused ion beam nanolithography to fabricate an ordered array of cups, which were then filled with colloidal nanoparticles using the most simple drop-casting and spin coating methods. The spectral and time-resolved studies of the samples with one or more nanocubes in the cup reveal a significant change in the radiation characteristics of QDs inside the nanoantenna. The Purcell effect causes an increase in the fluorescence decay rate (≥30) and an increase in the fluorescence intensity (≥3) of emitters in the HNA. Using the finite element method simulations, we have discovered that the proximity of the cups wall affects the oscillation modes of the gap plasmon, which, in turn, leads to changes in the electric field enhancement inside the nanoantenna gap. Additionally, substantial variations in the behavior of the gap plasmons at different polarizations of the exciting radiation have been revealed. The proposed nanoantenna can be useful in the development of plasmonic sensors, display pixels, and single-photon sources.

MXene Quantum Dot Synthesis, Optical Properties, and Ultra‐narrow Photonics: A Comparison of Various Sizes and Concentrations

AbstractTransition metal carbides and nitrides (MXene) quantum dots (QDs) are potentially important for versatile applications, including ultra‐narrow photonics. Here, a simple method for controlling the sizes and solution concentrations of Ti2C‐MXene‐QDs are shown, and then their optical properties are systematically investigated and compared. The nonlinear optical characteristics of QDs can be adjusted through the QD size and solution concentration. QDs with smaller sizes of 1–3 nm have stronger absorptivity, larger modulation depth and lower nonsaturable loss, and QDs with higher concentrations have stronger absorptivity and larger modulation depth but higher nonsaturable loss. These QDs are further applied to construct loop‐cavity ultranarrow lasers whose narrowest laser linewidth is 624.5 Hz, highest signal‐to‐noise ratio (SNR) is 77.63 dB and lowest power fluctuation is 0.4%. A comparison of these indicators indicates that smaller and more homogeneous MXene QD solutions with proper concentrations favor ultra‐narrow photonics. The laser power is also amplified to ≈60 mW by an erbium‐doped fiber amplifier (EDFA).