Uniform Quantum Dots Research Articles

Photocatalytic activity of green synthesized cadmium sulfide quantum dots on the removal of RhB dye and its cytotoxicity and antibacterial studies

Presence of inorganic pollutants in water reservoirs is the treating factor for human health and environment. Semiconductor quantum dots (QDs) has been regarded as one of the most efficient nanoparticles for their enhanced photocatalytic activity. Medicinal plants are the safe sources to provide green template for biosynthesis of inorganic nanoparticles such as quantum dots. In order to determine the photocatalytic and biological application of cadmium sulfide quantum dots (CdS QDs), a biosynthesis approach was employed using saffron (Crocus sativus L.) stigma extract as the green reaction substrate. The biosynthesis process was evaluated at different pH condition to obtain the most efficient CdS QDs. Characterization of prepared CdS QDs were determined through UV–vis and fluorescence spectroscopy, FTIR and TEM analysis. The obtained results showed well dsispersed and uniform QDs during green synthesis at the optimum condition. The absorption and electrical properties of green synthesized CdS QDs showed the lowest energy bandgap of 2.4 at pH 11. Photocatalytic activity of CdS QDs on Rhodamine B degradation showed 92% degradation after 80 min under UV light irradiation. The antibacterial and cell cytotoxicity of green synthesized CdS QDs were assayed by disk diffusion and MTT assays respectively. Obtained results showed significant antibacterial effect of CdS QDs against gram-positive and gram-negative bacteria including B. subtilis (90%) and E. coli (96%) respectively. Moreover, cytotoxicity of prepared CdS Qds through MTT assay indicated 79% apoptosis induction on MCF-7 breast cancer cells.

Analytical Model and Experimental Analysis to Estimate the Interdiffusion and Optoelectronic Properties of Coupled InAs Quantum Dots Post Rapid Thermal Processing

The stoichiometric variations in molecular beam epitaxy (MBE)-grown In(Ga)As quantum dots (QDs) after rapid thermal processing (RTP) is estimated from an analytical model assisted by transmission electron microscopy (TEM) images. A systematically grown multilayer (bi-, penta-, hepta-, and deca-layer) InAs Stranski–Krastanov (SK) QDs coupled electronically to submonolayer (SML) QDs are used in this study. The As-grown (ASG) samples are treated with RTP at temperatures of 650 °C, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$700~^{\circ }\text{C}$ </tex-math></inline-formula> , <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$750~^{\circ }\text{C}$ </tex-math></inline-formula> , and 800 °C for 30 s. Our model estimates a significant diffusion of In atoms in the growth direction compared with the in-plane direction altering the QD dimensions and composition. To check its reliability, we incorporated an eight-band k.p model on all the RTP-treated strained In(Ga)As QD heterostructures. Photoluminescence (PL) measurements reveal a strong correlation with the simulation results; furthermore, a strong PL blueshift (56 nm) and narrow linewidth from 67 nm (ASG) to 33 nm ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$800~^{\circ }\text{C}$ </tex-math></inline-formula> ) are seen due to an increase in the uniformity of QDs supporting the atomic force microscopy (AFM) results. AFM images reveal the formation of highly uniform and dense QDs with increased annealing temperature. The activation energy (AE) shows a decreasing trend due to the reduction in carrier confinement with RTP, agreeing with the analytical model. This is probably the first report that presents the effect of RTP on SK-SML coupled QD devices both in terms of theoretical and experimental analyses. This analytical model can thus be extended to any annealing study and for any material with certain known parameters and is helpful for futuristic studies.

A photoelectric synapse based on optimized perovskite CH3NH3PbBr3 quantum dot film detectors

In this work, we report a high-performance photodetector based on perovskite CH3NH3PbBr3 quantum dots (QDs) films with a configuration of Au/CH3NH3PbBr3 QDs-Al2O3-indium tin oxide/Au as a bioinspired photoelectric synapse. The uniform CH3NH3PbBr3 QDs thin film is fabricated by a electrodepositing QDs solution and exhibits favorable long-term stability at ambient. By inserting an Al2O3 film, the dark current of the QDs film photodetectors is significantly suppressed as a result of the blocking effect, accompanied by the enhanced ON/OFF ratio. Furthermore, the optimal photodetector is utilized as a photoelectric synapse. Through modulating the light pulse stimuli, some underlying synaptic functions, including paired-pulse facilitation, axon-multi-synapses network function, and the transformation from short-term plasticity to long-term plasticity, are flexibly emulated on a single photoelectric synapse. These remarkable results are promising for building hardware units with neuromorphic architecture to mimic the human brain functionalities.

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.

Electrochemical fabrication of ultrafine g-C3N4 quantum dots as a catalyst for the hydrogen evolution reaction

Because of its high concentration of in-plane elemental nitrogen, superior chemical/thermal stability, tunable electronic band structure and environmentally friendly nature, graphite-like carbon nitride (g-C3N4) is a new promising metal-free material that has drawn much attention in photo-/electric catalysis. Compared with the regulation of the band structure in photocatalysis, the deliberate synthesis of g-C3N4 electrocatalysts is mainly focused on the construction of catalytic sites and the modulation of the charge transfer kinetics. This work reports a rapid method for synthesizing ultrafine g-C3N4 quantum dots (QDs) by electrochemical exfoliation using Al3+ ions as an intercalation agent. Uniform g-C3N4 QDs with small lateral size and thickness were collected more easily due to the higher charge density and stronger electrostatic force of Al3+ ions in the lattice of the host material, compared to conventional univalent alkali cations. The QDs had an average lateral dimension and thickness of 3.5 nm and 1.0 nm, respectively, as determined by TEM and AFM measurements. The presence of a large number of C/N defects was verified by the UV-vis spectra. The ultrafine g-C3N4 QDs had a superior hydrogen evolution reaction performance with an ultra-low onset-potential approaching 0 V, and a low overpotential of 208 mV at 10 mA cm−2, as well as a remarkably low Tafel slope (52 mV·dec−1) in an acidic electrolyte.

PbS1−xSex-Quantum-Dot@MWCNT/P3HT Nanocomposites with Tunable Photoelectric Conversion Performance

The photoelectric performance of quantum dots (QDs)-based nanocomposites is closely related to the optical properties of QDs, which play a critical role in the optical absorption and separation/transfer of charge carriers. Herein, we report a nanocomposite composed of light absorber PbS1−xSex quantum dots (QDs), electron-conducting multiwalled carbon nanotubes (MWCNTs) and hole-conducting poly-3-hexylthiophene (P3HT) with tunable photoelectric conversion performance. In addition to using the quantization effect, we proposed solid-solution PbS1−xSex QDs (x = 0, 0.25, 0.5, 0.75, 1) for band gap engineering. In particular, we successfully synthesized relatively small (~5.3 nm) and uniform QDs via the hot-injection method by using PbCl2, S/Se powder and environmentally friendly oleylamine (OLA) as the precursors and/or solvent. By increasing the content of Se, the band gap of PbS1−xSex QDs decreased along with the decrease in the conduction band and valence band edges. The suitable energy level alignment enabled the efficient transfer of photoinduced charge carriers, and hence a much higher photoelectric conversion performance of the PbS1−xSex-QD@MWCNT/P3HT nanocomposites than the individual QDs, P3HT, and binary PbS1−xSex-QD@MWCNT, as well as the best performance, was achieved over PbS0.75Se0.25-QD@MWCNT/P3HT.

Internal optical loss and light-current characteristic in injection lasers

Possibility of tailoring the light-current characteristic (LCC) shape in quantum dot (QD) lasers by varying uniformity of QDs is discussed. Making the QD ensemble less uniform results in roll-over in the LCC. The second branch in the LCC appears with making the QD ensemble even less uniform.

Fabrication of multilayer 1D TiO2/CdS/ZnS with high photoelectrochemical performance and enhanced stability

Nano TiO2 is a basic photoanode material in the application of new type solar cell for its appropriate bandgap and photoemission. However, traditionally TiO2-based photoanode films are limited in weak photoresponse and effortless recombination. Herein, we increase light absorption range through combined the uniform CdS quantum dots (QDs) by successive ionic layer adsorption reaction (SILAR) method and decrease the recombination of photo-generated electrons/holes through ZnS passivation layer overlaying on TiO2/CdS. Photocurrent response (i-t), photocurrent density-voltage (J-V) curves of TiO2/CdS/ZnS demonstrated the photovoltaic conversion efficiency (η) has been reaching 3.43%, which has 230% and 33% improvement than pure TiO2 and TiO2/CdS.

Highly uniform GaSb quantum dots with indirect–direct bandgap crossover at telecom range

We demonstrate a new quantum-confined semiconductor material based on GaSb quantum dots (QDs) embedded in a single-crystalline AlGaSb matrix by filling droplet-etched nanoholes. The droplet-mediated growth mechanism allows formation of low QD densities required for non-classical single-QD light sources. The photoluminescence (PL) experiments reveal that the GaSb QDs have an indirect–direct bandgap crossover at telecom wavelengths. This is due to the alignment of the Γ and L valleys in the conduction band as a result of the quantum confinement controlled by the dimensions of the nanostructure. We show that in the direct bandgap regime close to 1.5 µm wavelength, the GaSb QDs have a type I band alignment and exhibit excitonic emission with narrow spectral lines and very low inhomogeneous broadening of PL emission owing to the high material quality and dimensional uniformity. These properties are extremely promising in terms of applications in infrared quantum optics and quantum photonic integration.

The role and growth of strain – reducing layer by molecular -beam epitaxy in a multi – stack InAs/(In,Ga)As sub - monolayer quantum dot heterostructure

Abstract The present study focuses on a growth strategy to achieve a uniform (and larger) dot size distribution in a multi-stack InAs/InGaAs sub-monolayer (SML) quantum dot (QD) heterostructure by capping with a varying InxGa1-xAs (x = 0.15) layer thickness (Y). The InxGa1-xAs layer serves both as matrix medium for the dot growth and strain - reducing layer (SRL) to preserve the QD morphology from decomposition. The dots capped by an optimum SRL or capping layer (CL) thickness will alleviate from dot segregation or intermixing, surface diffusion and dot inhomogeneity effects, thus paving way to grow a nearly defect - free quantum dot heterostructure. The experimental calculations on low – temperature (19 K), high – excitation power (1.1 kW/cm2) photoluminescence (PL) revealed ground – state (GS) emission energies at 1.12, 1.14, 1.09 eV for 2, 4, and 6 ML SRL thickness respectively. While, the presence of QD excited state (ES) transitions has been analysed using PL - excitation (PLE) spectroscopy, as the CL will highly alter the band offsets as well as strain inside QDs. The interfacial structural quality, strain relaxation in QDs due to SRL was inspected through high-resolution X – ray diffraction (HRXRD) and Raman measurements. The self – consistent Schrodinger – Poisson solver based on 8 – band k.p formulation was used to evaluate the PL energy and strain profile as a comparison to experimental data. Hence, the sample containing 2 ML CL thickness showed superior results in terms of PL emission and strain, which leads towards the growth of uniform QDs for photodetector (PD) applications operating in the short – wave infrared (SWIR) regime (λ: 0.9 μm–2.5 μm, Energy: 1.377 eV - 0.495eV).

Optical properties and symmetry optimization of spectrally (excitonically) uniform site-controlled GaAs pyramidal quantum dots

GaAs quantum dots (QDs) have recently emerged as state-of-the-art semiconductor sources of polarization-entangled photon pairs, however, without site-control capability. In this work, we present a systematic study of epitaxially grown GaAs/AlxGa1-xAs site-controlled pyramidal QDs possessing unrivaled excitonic uniformity in comparison to their InGaAs counterparts or GaAs QDs fabricated by other techniques. We have experimentally and systematically investigated the binding energy of biexcitons, highlighting the importance of the uniformity of all excitonic lines, rather than concentrating solely on the uniformity of the neutral exciton as a typical figure of merit, as it is normally done in the literature. We present optical signatures of GaAs QDs within a range of ∼250 meV with a remarkable uniformity within each individual sample, the ability to excite the biexciton state resonantly, and a systematic study of the fine-structure splitting (FSS) values—features important for polarization entangled photon emission. While, in general, we observe relatively large FSS distribution and associated non-uniformities, we discuss several strategies to suppress the average FSS values to &amp;lt;15 μeV.

Luminescent MoS2 Quantum Dots with Tunable Operating Potential for Energy-Enhanced Aqueous Supercapacitors.

Wide band gap luminescent MoS2 quantum dots (QDs) and MoS2 nanocrystals (NCs) have been synthesized by using laser-assisted chemical vapour deposition and used as an electrode material in supercapacitors. Size-dependent properties of the MoS2 QDs and NCs were examined by UV–vis absorption, photoluminescence, and Raman spectroscopy. The morphological evolution of the NCs and QDs were characterized by using field emission scanning electron microscopy, high-resolution transmission electron microscopy, and atomic force microscopy. The as-synthesized uniform QDs with a size of ∼2 nm exhibited an extended electrochemical potential window of 0.9 V with a specific capacitance value of 255 F/g, while the NCs values were 205 F/g and 0.8 V and the pristine MoS2 with values of 105 F/g and 0.6 V at a scan rate of 1 mV s–1. A shorter conductive pathway and 3D quantum confinement of MoS2 QDs that exhibited a higher number of active sites ensure that the efficient charge storage kinetics along with the intercalation processes at the available edge sites enable significant widening of operating potential window and enhance the capacitance. The symmetric device constructed with the QDs showed a remarkable device capacitance of 50 F/g at a scan rate of 1 mV s–1 with an energy density of ∼5.7 W h kg–1 and achieved an excellent cycle stability of 10,000 consecutive cycles with ∼95% capacitance retention.

From the Editor

Layered silicates present interaction sites at both faces and edges of the nanolayers and silane coupling agents that locate at both sites lead to polymer nanocomposites with superior melt strength and properties. This work’s objective was (a) to investigate the effectiveness of solvent-free, vapor phase, silane treatment of the nanolayers for formulating masterbatches and (b) to compare the mechanical properties of 1mil thick blown films from polypropylene copolymer nanocomposites with such coupling, to films from the neat polypropylene. The nanocomposite blown film tensile modulus and tensile strength improved along both the draw direction and the transverse direction. In addition, their elongation to failure was close to 500% along both directions, in contrast to values of 500% along MD and 170% along TD for the neat PP copolymer. These trends may be understood in terms of the crystalline lamellar orientation distribution in the films. FESEM images revealed that cross-hatched lamellae were absent from the unfilled PP blown film and were pervasive in the nanocomposite blown film. The nanolayers were oriented in the film plane with the longer dimension largely along the MD. The lower extent of lamellar orientation around nanolayers may be attributed to the strong reduction in the polymer chain mobility attached to the nanolayers. Polyaniline and quantum dot-based nanostructures: Developments and perspectives” also by Ayesha Kausar reviews Quantum dots which are 2–5 nm nanoparticles with exceptional optical, electronic, luminescence, and semiconducting properties. Polyaniline is an exclusive conjugated polymer. This article reviews recent efforts, scientific trials, and technological solicitations for polyaniline/quantum dot-based nanocomposites. Polyaniline/quantum dot mixtures form a unique composition for advance materials and applications. Carbon dots, graphene quantum dots, and several inorganic quantum dots have been added to a conducting polymer. A functional quantum dot may develop electrostatic, van der Waal, and p–p stacking interactions with the conjugated polymer backbone. Uniform quantum dot dispersion in polyaniline may result in inimitable morphology, electrical conductivity, electrochemical properties, capacitance, and sensing features. Finally, this review expounds on the many applications for polyaniline/quantum dot nanocomposites including dye-sensitized solar cell, supercapacitor, electronics, gas sensor, biosensor, and bioimaging. And a final thought. “The power of population is so superior to the power of the Earth to produce subsistence for man, that premature death must in some shape or other visit the human race” Thomas Malthus 1798

Planarized spatially-regular arrays of spectrally uniform single quantum dots as on-chip single photon sources for quantum optical circuits

A long standing obstacle to realizing highly sought on-chip monolithic solid state quantum optical circuits has been the lack of a starting platform comprising scalable spatially ordered and spectrally uniform on-demand single photon sources (SPSs) buried under a planar surface. In this paper, we report on the first realization of planarized SPS arrays based on a unique class of shape-controlled single quantum dots (SQDs) synthesized on mesa top (dubbed MTSQDs) using substrate-encoded size-reducing epitaxy (SESRE) on spatially regular arrays of patterned nanomesas with edge orientation chosen to drive symmetric adatom migration from the nanomesa sidewalls to the top, thereby enabling spatially selective growth. Specifically, on GaAs(001) square nanomesas with edges along ⟨100⟩, we synthesized binary GaAs/InAs/GaAs MTSQDs emitting around 1120 nm with 1.8 nm standard deviation and single photon emission purity &amp;gt;99.5%. SESRE based MTSQDs are shown for the first time to lend themselves to planarization of the surface morphology when grown on pedestal shape mesas. We demonstrate that the planarizing overgrowth process over arrays of InGaAs SQDs largely maintains the SQDs’ high single photon emission purity (&amp;gt;98%) and spectral uniformity (∼5 nm). Such planarized SQD arrays offer the long-sought platform for on-chip integration with light manipulating structures to realize quantum optical circuits.

High-Yield Production of Water-Soluble MoS2 Quantum Dots for Fe3+ Detection and Cell Imaging.

Uniform water-soluble MoS2 quantum dots (WS-MSQDs) were synthesized via a sequential combination of sintering/etching/exfoliation method and solvothermal route. The obtained WS-MSQDs with average size of approximately 3.4 nm exhibited sufficient water solubility and remarkable fluorescence properties. The WS-MSQDs were utilized as a probe for detection of Fe3+ ions with high selectivity and specificity. Furthermore, the WS-MSQDs exhibited high fluorescence stability under different conditions. Finally, the WS-MSQDs were successfully applied for the fluorescence imaging of Fe3+ in living cells, which exhibited practical potential for biomedical applications.

P‐107: Inkjet Printed Uniform Quantum Dots as Color Conversion for Active Matrix Micro‐LED Display

Quantum dots (QDs) display have attracted much attention due to their excellent optical properties and solution process. Especially, QDs can act as effective color conversion for light emitting diodes (LEDs). In this work, we fabricated 4‐inch QD‐microLED display panel by inkjet printing technology, being cooperated with active matrix inorganic microLEDs. Here blue Micro‐LED acted as backlight, patterned red and green QD layer acted as converted materials, which exhibited high quantum efficiency, high luminance, high color purity. We believe that inkjet‐printed QD display with blue microLEDs would be promising candidate for the next generation display in the near future.

Surfactant-Free Green Synthesis of ZnS QDs with Active Surface Defects for Selective Nanomolar Oxalic Acid Colorimetric Sensors at Room Temperature

Quantum dots (QDs) are synthesized using surfactants to enable their viable applications with minimum surface defects. The environmentally benign method without a surfactant is a way forward for sustainable applications. Sunlight-mediated synthesis of uniform ZnS QDs without a surfactant is achieved with pristine surface defects that facilitate visible light absorption. The cubic phase of QDs and their size are revealed using transmission electron microscopy and X-ray diffraction. The unique absorption property is utilized to demonstrate a cost-effective colorimetric sensor for biological toxic substances such as oxalic acid using absorption spectroscopy. The unparalleled performance among the enzymatic or nonenzymatic processes for oxalic acid detection is realized, however, without any noble metal, for a wide range of 1 nM to 0.5 mM concentrations with a limit of detection of 0.2 nM. Typical inferences from organic acids, water-soluble salts, and metal ions are also investigated. Further, the role of surface defects in QDs is unfurled with photoluminescence, infrared, and Raman spectroscopic measurements, and the underlying mechanism of OA detection is elaborated. Thus, green synthesis and unmasking the influence of surface defects in ZnS QDs as demonstrated for selective detection open up for various other applications such as solar cells and catalysts.

System makes quantum dots autonomously

By combining artificial intelligence (AI), machine learning, and microfluidics, researchers have designed an autonomous decision-making synthesis system that chooses optimal reagents, synthetic routes, and reaction conditions to make valuable products with targeted properties. Dubbed “Artificial Chemist,” the system uses tiny quantities of precursors and does not require experienced users to monitor and guide experiment choices. The system, which learns from successive experiments, can reduce the time, cost, and quantity of waste associated with traditional R&D synthesis (Adv. Mater. 2020, DOI: 10.1002/adma.202001626). In a proof-of-concept study, Robert W. Epps and Milad Abolhasani of North Carolina State University and coworkers used the system to make a series of uniform colloidal perovskite quantum dots with preselected emission profiles and other electronic properties. These materials are used in solar cells, light-emitting diodes, and electronic displays. Fitted with syringe pumps, micromixers, and built-in spectroscopy probes, Artificial Chemist reacted cesium lead bromide, zinc halides, and organic

SnO2 Quantum Dots: Rational Design to Achieve Highly Reversible Conversion Reaction and Stable Capacities for Lithium and Sodium Storage.

SnO2 has been considered as a promising anode material for lithium-ion batteries (LIBs) and sodium ion batteries (SIBs), but challenging as well for the low-reversible conversion reaction and coulombic efficiency. To address these issues, herein, SnO2 quantum dots (≈5 nm) embedded in porous N-doped carbon matrix (SnO2 /NC) are developed via a hydrothermal step combined with a self-polymerization process at room temperature. The ultrasmall size in quantum dots can greatly shorten the ion diffusion distance and lower the internal strain, improving the conversion reaction efficiency and coulombic efficiency. The rich mesopores/micropores and highly conductive N-doped carbon matrix can further enhance the overall conductivity and buffer effect of the composite. As a result, the optimized SnO2 /NC-2 composite for LIBs exhibits a high coulombic efficiency of 72.9%, a high discharge capacity of 1255.2 mAh g-1 at 0.1 A g-1 after 100 cycles and a long life-span with a capacity of 753 mAh g-1 after 1500 cycles at 1 A g-1 . The SnO2 /NC-2 composite also displays excellent performance for SIBs, delivering a superior discharge capacity of 212.6 mAh g-1 at 1 A g-1 after 3000 cycles. These excellent results can be of visible significance for the size effect of the uniform quantum dots.

Polyaniline and quantum dot-based nanostructures: Developments and perspectives

Quantum dots are 2–5 nm nanoparticles with exceptional optical, electronic, luminescence, and semiconducting properties. Polyaniline is an exclusive conjugated polymer. This article reviews recent efforts, scientific trials, and technological solicitations of the polyaniline/quantum dot-based nanocomposites. Polyaniline/quantum dot mixtures form a unique composition for advance materials and applications. Carbon dots, graphene quantum dots, and several inorganic quantum dots have been added to a conducting polymer. A functional quantum dot may develop electrostatic, van der Waal, and π–π stacking interactions with the conjugated polymer backbone. Uniform quantum dot dispersion in polyaniline may result in inimitable morphology, electrical conductivity, electrochemical properties, capacitance, and sensing features. Finally, this review expounds on the many applications for polyaniline/quantum dot nanocomposites including dye-sensitized solar cell, supercapacitor, electronics, gas sensor, biosensor, and bioimaging.