Growth Of Quantum Dots Research Articles

Colloidal Multi-Dot Nanorods.

Colloidal nanorod heterostructures consisting of multiple quantum dots within a nanorod (n-DNRs, where n is the number of quantum dots within a nanorod) are synthesized with alternating segments of CdSe "dot" and CdS "rod" via solution heteroepitaxy. The reaction temperature, time dependent ripening, and asymmetry of the wurtzite lattice and the resulting anisotropy of surface ligand steric hindrance are exploited to vary the morphology of the growing quantum dot segments. The alternating CdSe and CdS growth steps can be easily repeated to increment the dot number in unidirectional or bidirectional growth regimes. As an initial exploration of electron occupation effects on their optical properties, asymmetric 2-DNRs consisting of two dots of different lengths and diameters are synthesized and are shown to exhibit a change in color and an unusual photoluminescence quantum yield increase upon photochemical doping.

One-pot heat-up synthesis of short-wavelength infrared, colloidal InAs quantum dots.

III-V colloidal quantum dots (QDs) promise Pb and Hg-free QD compositions with which to build short-wavelength infrared (SWIR) optoelectronic devices. However, their synthesis is limited by the availability of group-V precursors with controllable reactivities to prepare monodisperse, SWIR-absorbing III-V QDs. Here, we report a one-pot heat-up method to synthesize ∼8nm edge length (∼6.5nm in height) tetrahedral, SWIR-absorbing InAs QDs by increasing the [In3+]:[As3+] ratio introduced using commercially available InCl3 and AsCl3 precursors and by decreasing the concentration and optimizing the volume of the reducing reagent superhydride to control the concentration of In(0) and As(0) intermediates through QD nucleation and growth. InAs QDs are treated with NOBF4, and their deposited films are exchanged with Na2S to yield n-type InAs QD films. We realize the only colloidal InAs QD photoconductors with responsivity at the technologically important wavelength of 1.55μm.

Batch preparation process of composite materials of quantum dot glass and polystyrene used in backlight displays

All-inorganic CsPbX3 quantum dots (X = Cl, Br, or I) are regarded as a new generation of efficient luminescent materials for displays and solid-state lighting due to their excellent optoelectronic properties. However, the poor stability of CsPbX3 quantum dots severely hampers their commercial applications. Currently, the in-situ growth of CsPbX3 quantum dots in amorphous glass has emerged as a crucial approach to significantly enhance their stability. This study successfully synthesized large-scale CsPbBr3@glass materials using a one-step self-crystallization method involving melting, quenching, and heat treatment. CsPbBr3@glass was blended with polystyrene (PS) through melt blending and extrusion, resulting in the fabrication of a CsPbBr3@glass@PS film. By controlling the content of quantum dot glass in polystyrene and adjusting the film's thickness, a green light film with color coordinates (0.1629, 0.7759) and a Full Width Half Maximum (FWHM) of 19.78 nm was achieved. The film produced through this process demonstrated exceptional stability, retaining 90% of its luminous intensity after 1000 h of rigorous aging experiments. Furthermore, when combined with potassium fluorosilicate composite polystyrene film and a blue light chip, a 7-inch LCD display with a color gamut of 135.8% of NTSC 1953 and 92.8% of Rec. 2020 was successfully assembled. This research holds significant reference value for the commercial application of quantum dot glass.

The effect of In(Ga)As/GaAs quantum dots on the optical loss of photonic crystal cavities

We present a systematic investigation of the optical losses in GaAs photonic crystal cavities with and without embedded self-assembled In(Ga)As quantum dots (QDs) to shed light on additional loss mechanisms related to the presence of the QDs. To clarify the role of the measurement method, we propose an experimental configuration where the optical properties can be evaluated simultaneously through reflection and photoluminescence measurements. Independently of the measurement method, we observe a reduced quality (Q) factor in cavities with embedded QDs when compared to the passive counterparts. Our analysis indicates that these additional losses—about 7 GHz—are unrelated to direct excitonic absorption for the investigated areal QD densities of 175 μm−2. We analyze several mechanisms which could explain our observations and suggest that a possible origin could be unsaturable absorption from midgap defects introduced by the QD growth.

Epitaxial growth and characterization of multi-layer site-controlled InGaAs quantum dots based on the buried stressor method

We report on the epitaxial growth, theoretical modeling, and structural as well as optical investigation of multi-layer, site-controlled quantum dots fabricated using the buried stressor method. This deterministic growth technique utilizes the strain from a partially oxidized AlAs layer to induce site-selective nucleation of InGaAs quantum dots. By implementing strain-induced spectral nano-engineering, we achieve spectral control of emission and a local increase in the emitter density. Furthermore, we achieve a threefold increase in the optical intensity and reduce the inhomogeneous broadening of the ensemble emission by 20% via stacking three layers of site-controlled emitters, which is valuable for using the SCQDs as a gain medium in microlaser applications. Our optimization of site-controlled growth of quantum dots enables the development of high-β microlasers with increased confinement factor.

Scalable Bright and Pure Single Photon Sources by Droplet Epitaxy on InP Nanowire Arrays.

High-quality quantum light sources are crucial components for the implementation of practical and reliable quantum technologies. The persistent challenge, however, is the lack of scalable and deterministic single photon sources that can be synthesized reproducibly. Here, we present a combination of droplet epitaxy with selective area epitaxy to realize the deterministic growth of single quantum dots in nanowire arrays. By optimization of the single quantum dot growth and the nanowire cavity design, single emissions are effectively coupled with the dominant mode of the nanowires to realize Purcell enhancement. The resonance-enhanced quantum emitter system boasts a brightness of millions of counts per second with nanowatt excitation power, a short radiation lifetime of 350 ± 5 ps, and a high single-photon purity with g(2)(0) value of 0.05 with continuous wave above-band excitation. Finite-difference time-domain (FDTD) simulation results show that the emissions of single quantum dots are coupled into the TM01 mode of the nanowires, giving a Purcell factor ≈ 3. Our technology can be used for creating on-chip scalable single photon sources for future quantum technology applications including quantum networks, quantum computation, and quantum imaging.

Monolithic Passive−Active Integration of Epitaxially Grown Quantum Dot Lasers on Silicon

Monolithic Passive−Active Integration of Epitaxially Grown Quantum Dot Lasers on Silicon

Size control of MoS2 quantum dots by varying the crystallographic orientation of sapphire substrates

The phenomena in size-dependent optoelectronic and catalytic properties of MoS2 quantum dots make them attractive in fabricating optoelectronic devices and processing water-splitting. However, growing monolayered MoS2 quantum dots with controlled sizes is challenging and has never been realized on a solid-state substrate. Herein, we experimentally demonstrate the size of monolayered MoS2 quantum dots can be thermodynamically manipulated by varying the orientation of the sapphire substrate from c plane, m plane to r plane and the size can be tuned from 10 nm to 2 nm. An apparent shift in the optical absorption and outstanding size-dependent electrocatalytic capability of the MoS2 quantum dots can be featured. The DFT results verify that the size modulation is associated with the interaction strength between the MoS2 quantum dots and the sapphire substrate. This work provides a new benchmark in the growth of size-tunable monolayered MoS2 quantum dots on a solid-state substrate.

Sequential Growth of InP Quantum Dots and Coordination between Interfacial Heterovalency and Shell Confinement: Implication for Light-Emitting Devices

Sequential Growth of InP Quantum Dots and Coordination between Interfacial Heterovalency and Shell Confinement: Implication for Light-Emitting Devices

Growth of Medium-Sized InP Quantum Dots with High Photoluminescence Efficiency and Enhanced Stability

This study introduces medium-sized core/shell InP quantum dots (QDs) with high photoluminescence (PL) efficiency and remarkable material stability. The incorporation of a ZnSe interlayer between the core and the thicker outer ZnS shell enhances both the optical performance and material stability. When further increasing the S/Se ratio to synthesize larger QDs with a thicker ZnS layer, optical performance significantly declines despite the improvement in stability. To achieve QDs with superior optical performance and stability, we controlled the S/Se ratio variation during shell growth and examined its impact on the structure, morphology, and size of InP QDs. Our approach resulted in medium-sized InP/ZnSe/ZnS QDs with tunable wavelengths (606-630 nm), PL quantum yields (PLQY) > 90%, full width at half maximum (FWHM) values < 40 nm, and enhanced material stability.Keywords: indium phosphide (InP), quantum dots (QDs), high efficiency and stability, S/Se ratio of shell, medium-size quantum dots, stainless steel reactor Figure 1

Impact of Pocket Geometry on Quantum Dot Lasers Grown on Silicon Wafers

Epitaxially grown quantum dot (QD) lasers in narrow pockets on patterned silicon photonics wafers present a key step toward full monolithic integration of on‐chip light sources. However, InAs QD lasers grown in deep and narrow pockets demonstrate limited performance and reliability compared to planar‐grown counterparts. Herein, InAs QD lasers are grown in patterned SiO2 pockets atop planar thermal cyclic annealed GaAs on (001) Si substrate with reduced threading dislocation density, enabling detailed study of how pocket geometry impacts device performance. Fabry–Pérot lasers with cleaved facets exhibit strong variation in performance based on the dimensions of the pocket, wherein thermal and optical metrics improve with increasing pocket width. Devices lase up to a maximum stage temperature of 115 °C with an extrapolated lifetime of 2.2 years at 80 °C for material grown in 50 μm by 3900 μm pockets. This study addresses, the ongoing challenge of optimizing pocket‐grown devices to planar equivalent performance.

In situ growth of Ag2S quantum dots on cellulose nanocrystals and their near-infrared bioimaging performance

Elongated nanoparticles show distinct advantages over spherical nanoparticles in bioimaging because of surface area-to-volume, rate of clearance from the body and elimination mechanism. In this work, we investigated the fluorescence emission properties of the hybrid system by decorating silver sulfide quantum dots (Ag2S QDs) in situ on the surface of cellulose nanocrystal (CNC) with unique rod shape, modifiability and biocompatibility. This water-dispersible fluorescent probe has both absorption and fluorescence in near-infrared (NIR) region. By varying the amount of surface ligands, uniformly dispersed Ag2S QDs with different crystalline states but similar sizes were prepared due to the anchoring effect of CNC. The fluorescence quantum yield of fluorescent probes can be improved up to 109-fold (from 0.04 % to 4.36 %). In addition, the CNC-restricted interparticle spacing of Ag2S QDs (< 10 nm), in combination with the overlap of wide fluorescence emission and ultraviolet absorption, significantly enhanced the 1070 nm emission in the NIR-II region via fluorescence resonance energy transfer (FRET). Further conjugation of these CNC probes with folic acid-polyethylene glycol-amino (FA-PEG-NH2) enables in vitro bioimaging of Hela cells, which are potentially applicable for in vivo cancer detection system. The synthetic strategy provides a new way for one-pot preparation of fluorescent probes with both high NIR-I absorption and NIR-II fluorescence.

Breaking AgInTe2 Quantum Dot Chain to Fabricate AgInTe2-ZnS Janus Nanocrystals.

Colloidal multinary chalcogenides (MnCs) have emerged as excellent optoelectronic materials, where S- and Se-based MnCs show considerable progress; however, the Te counterpart suffers from detrimental surface oxidation. Moreover, Te-based I-III-VI MnCs (e.g., AgInTe2) tend to form a one-dimensional (1-D) anisotropic structure via the self-assembly of surface-oxidized Te, thus restricting the isolation of AgInTe2 quantum dots (QDs). We report successful control of the self-assembly of Te-based MnCs to arrest the growth of AgInTe2 QDs by using a synergistic capping agent (dodecanethiol and oleic acid). The reaction proceeds with several intermediates, including hexagonal microrods (MR), tetragonal QDs in a chain arrangement, and tetragonal MRs. Importantly, we note that the incorporation of ZnS QDs triggers the breaking of the chain arrangement of the AgInTe2 QDs and the emergence of evenly distributed AgInTe2-ZnS Janus nanocrystals with significantly reduced long-term Te-oxidative properties. Arresting the AgInTe2 QD chain and the subsequent Janus nanocrystal formation could have promising opportunities for 1-D charge hopping and efficient charge transport for optoelectronic applications, respectively.

Visible-light S-scheme heterojunction of copper bismuthate quantum dots decorated Titania-spindles for exceptional tetracycline degradation

The rational heterojunctions for antibiotics degradation have sparked significant attention in wastewater purification. In this study, we report a unique S-scheme photocatalytic system by in-situ growth of CuBi2O4 quantum dots (QDs) onto {101} facet of TiO2 spindles (TiO2-P) via hydrothermal transformation of Na-titanate nanotubes, which is observed by transmission electron microscopy technology. The CuBi2O4/TiO2-P effectively achieves photo-degradation of tetracycline (TC) using visible light (e.g. an 82% TC degradation efficiency at 60 min), which is attributed to the promotion of the charge separation and retaining strong redox capacity at the heterojunction interfaces via the active species of O2−, OH, and h+. Moreover, density functional theory (DFT) calculations show that a built-in electric field forms at the interface of the S-scheme heterojunction. In all, this work introduces a straightforward in-situ hydrothermal growth method to construct S-scheme photocatalysts for effective water treatment.

Direct Growth of Nitrogen-Doped Carbon Quantum Dots on Co9S8 Passivated on Cotton Fabric as an Efficient Photoelectrode for Water Treatment.

Heterogeneous growth of photocatalysts on different porous substrates is a solution to avoid secondary pollution caused by composite photocatalysts themselves. However, the heterogeneous growth of composite photocatalysts with nitrogen-doped carbon quantum dots (NCQDs) inclusions-introduced during synthesis-impedes the direct growth on the substrate. To overcome this problem, NCQDs were grown on a Co9S8 (NCQDs-G@Co9S8) layer, decorated on cotton fabric. This optimal coupling mode of NCQDs and Co9S8 showed 54% degradation, compared to 33% dye degradation via NCQDs-doped Co9S8 (NCQDs-D@Co9S8). The change in the crystal structure and its lower loading on fabric results in significantly lower performance of NCQDs-D@Co9S8. Even with the combination of both surface growth and doping (NCQDs-DG@Co9S8), the performance was still limited to 42%. In addition, the optimum growth concentration of NCQDs on Co9S8 was observed for 7.5 w/w %, resulting in 92% photocatalytic activity (PCA) in 80 min. Comparing different surface states formed in NCQDs using different solvents, water-based surface states (oxygen-rich surface) are most suitable for the dye degradation. NCQDs-G@Co9S8 also offers 67% Cr-VI reduction to Cr-III, showing its suitability for both inorganic and organic compounds. Better electrode performance was related to suitable charge separation of the composite, where -OH groups mainly contribute in the photocatalytic dye degradation..

Acid-Resistant Near-Infrared II Ag2Se Quantum Dots for Gastrointestinal Imaging.

With the development of near-infrared II (NIR-II) fluorescence imaging, Ag2Se quantum dots (QDs) have become promising label candidates due to their negligible toxicity and narrow band gap. Despite their potential for gastrointestinal (GI) imaging, the application of Ag2Se QDs still presents significant challenges due to issues such as fluorescence extinction or poor stability in the complex digestive microenvironment. Herein, we have proposed a novel approach to the continuous production of Se precursors using glutathione (GSH) as the reductant under acidic conditions, realizing the continuous growth of water-dispersible Ag2Se QDs. The Ag2Se QDs emitting at 600-1100 nm have been successfully synthesized. Meanwhile, the silver-rich surface of the synthesized NIR-II Ag2Se QDs has been passivated well with the dense GSH, resulting in exceptional colloidal stability and photostability and endowing them with acid resistance. As a result, the obtained NIR-II Ag2Se QDs have exhibited remarkable stability in gastric acid, thus enabling their utilization for long-term real-time monitoring of GI peristalsis via NIR-II fluorescence imaging. Moreover, in contrast to conventional barium meal-based X-ray imaging, NIR-II fluorescence imaging with as-prepared NIR-II Ag2Se QDs can offer clearer visualization of fine intestinal structures, with a width as small as 1.07 mm. The developed strategy has offered a new opportunity for the synthesis of acid-resistant nanocrystals, and the acid-resistant, low-toxicity, and biocompatible NIR-II Ag2Se QDs synthesized in this work show a great promise for GI imaging and diagnosis of GI diseases in vivo.

Effect of CaO on crystallization and photoluminescence of CsPbBr3 quantum dots germanium borate glass

In recent years, perovskite quantum dots (QDs) have emerged as a star of the materials world based on their extraordinary optical properties. Nevertheless, the photoluminescence performance (PL) and stability of QDs need to be further improved. In this work, CsPbBr3 QDs glass with high photoluminescence quantum yield (PLQY) and excellent hydro-stability was manufactured utilizing a high temperature fusion process and followed heat treatment. By adjusting the concentration of CaO, the PLQY of CsPbBr3 QDs glass increased from 7.78% to 64.52%. The consequence confirmed that CaO addition loosened the glass structure together with accelerated atomic migration and reorganization at lower polymerization states, thereby promoting the precipitation and growth of QDs. Significantly, after 33 days of immersion testing, the glass sample maintained excellent luminescence, which was attributed to the protection of the PbBr(OH) hydration layer. Furthermore, CsPbBr3 QDs glass maintained 71% of original PL intensity after three heating and cooling cycles, indicating that the prepared sample had good thermal stability. This work provided new insights into the relationship between network structure and CsPbBr3 QDs crystallization, and had certain reference value for improving the PL performance and water stability of CsPbBr3 QDs.

MBE-based growth of Sn-rich quantum wells and dots at low Sn deposition rates

MBE-based growth of Sn-rich quantum wells and dots at low Sn deposition rates

Enhanced photocatalytic hydrogen production from Co-MOF/CN by nitrogen and sulfur co-doped coal-based carbon quantum dots

A novel composite photocatalyst for photocatalytic decomposition of water for hydrogen evolution was successfully synthesized by in-situ growth of nitrogen and sulfur co-doped coal-based carbon quantum dots (NSCQDs) nanoparticles on the surface of sheet cobalt-based metal-organic framework (Co-MOF) and graphitic carbon nitride (g-C3N4, CN). The structure and properties of the obtained catalysts were systematically analyzed. NSCQDs effectively broaden the absorption of Co-MOF and CN in the visible region. The new composite photocatalyst has high hydrogen production activity and the hydrogen production rate reaches 6254 μmol/(g·h) at pH = 9. At the same time, NSCQDs synergy Co-MOF/CN composites have good stability. After four cycles of hydrogen production, the performance remains relatively stable. The transient photocurrent response and Nyquist plot experimental results further demonstrate the improvement of carrier separation efficiency in composite catalysts. The semiconductor type (n-type semiconductor) of the single-phase catalyst was determined by the Mott–Schottky test, and the band structure was analyzed. The conductive and valence bands of CN are −0.99 and 1.72 eV, respectively, and the conduction and valence bands of Co-MOF are −1.85 and 1.33 eV, respectively. The mechanism of the photocatalytic reaction can be inferred, that is, Z-type heterojunction is formed between CN and Co-MOF, and NSCQDs was used as cocatalyst.

Self‐Assembled InAs Quantum Dots on InGaAsP/InP(100) by Modified Droplet Epitaxy in Metal–Organic Vapor Phase Epitaxy around the Telecom C‐Band for Quantum Photonic Applications

The growth of InAs quantum dots (QDs) by droplet epitaxy (DE) in metal–organic vapor phase epitaxy is demonstrated for the first time on an InGaAsP layer lattice matched to InP(100). The nucleation of indium droplets on InGaAsP shows a strong dependence on the deposition temperature, with an unexpectedly low density, pointing to a strongly increased surface diffusion compared to bare InP or InGaAs surfaces previously reported. Droplets and surface morphology are characterized via atomic force microscopy and scanning electron microscopy. Droplet crystallization into InAs QDs is explored, where the crystallization process follows a modified DE growth which resembles the one on InGaAs but strongly differs from bare InP. Also, no formation of quantum dashes (QDashes) is observed, as the DE growth technique used here allows for a better control of QD nucleation, decoupled from the layer/epilayer mismatch, favoring the formation of QDs over QDashes. Optical characterizations suggest a more efficient carrier capture into the QDs if these are grown on InGaAsP compared to InGaAs. Finally, bright single‐dot emission at low‐temperature is detected from QDs ranging from 1300 to 1600 nm, covering the technologically relevant telecom C‐band.