Quantum Dot Nanostructures Research Articles

Rapidly synthesis of AuM (M = Pt, Pd) hexagonals/graphene quantum dots nanostructures and their application for non-enzyme hydrogen peroxide detection

Rapidly synthesis of AuM (M = Pt, Pd) hexagonals/graphene quantum dots nanostructures and their application for non-enzyme hydrogen peroxide detection

Investigating the optical and magnetic properties of engineered multifunctional graphene oxide and potential application in medical physics and nonlinear optics‏

Herein, the synthesis of multifunctional engineered GOs with the structure of GO@Fe3O4-ligands-CdTe quantum dots (QDs) by an environment-friendly aqueous method was reported. l-cystein (Cys), 3-trimethoxysilyl-propanethiol (TMSP), and glutathione (GSH) were selected as ligands. The as-prepared GO@Fe3O4-ligands-CdTe QDs hybrid nanostructures were characterized by different methods. The findings indicate that the nanocomposites of GO@Fe3O4–ligands–CdTe QDs demonstrate superparamagnetic properties at room temperature. The saturation magnetization values for GO@Fe3O4, GO@Fe3O4-Cys-CdTe, GO@Fe3O4-GSH-CdTe, and GO@Fe3O4-TMSP-CdTe, are 25, 14, 16, and 2 emu g−1, respectively. These nanocomposites show stable and strong luminescence at 580-600 nm. The magnetic nanostructures also reveal the absorption wavelength at 300-490 nm. Using TMSP ligand as a bridge between QDs and magnetic GOs, the luminescence of the nanostructure has not decreased much compared to CdTe QDs. The use of Cys ligand preserves the saturation magnetism of the nanocomposite more than magnetic GO, and the dispersed nanostructure is stable in water. Furthermore, the transverse and longitudinal optical (TO and LO) phonon modes of prepared GO@Fe3O4–ligands–CdTe QDs were obtained by Kramers-Kronig (KK) relations based on fourier-transform infrared (FTIR) spectroscopy. The Z-scan results show that the type of used ligand has a great effect on the nonlinear optical (NLO) properties of the final product. The largest NLO parameters are related to GO@Fe3O4- TMSP -CdTe QDs, and the values of nonlinear absorption coefficient and nonlinear refractive index were obtained as 2.17×10−3(cm/W) and10.27×10−8(cm2/W), respectively. As a result, GO@Fe3O4–ligands–CdTe QDs nanostructures can be considered as promising multifunctional nanostructures for various biomedical applications and NLO devices.

Phase sensitive slow light in semiconductor quantum dots

This article presents a theoretical investigation of phase-controlled propagation of slow light under an electromagnetically induced transparency window in a multilayered one-dimensional photonic crystal with semiconductor quantum dot nanostructures as defects. To achieve the electromagnetically induced transparency window, a setup utilizes a faint probe laser pulse alongside two powerful control laser beams arranged in a closed-loop cascade configuration. In this arrangement, a significant Kerr nonlinearity, approximately on the scale of ∼10−13m2/V2, is discerned within the quantum dot nanostructures at a probe wavelength of 1.55 μm. It is observed that both the amplitude and the phase relationship of the control Rabi frequencies play crucial roles in governing the dynamics of the group velocity of the probe field in the quantum dot nanostructures. Under the regime of electromagnetically induced transparency, the group velocity of the probe field is significantly reduced, approximately by a factor of 103 times as compared to the light speed in free space. These findings hold promise for potential applications in nonlinear optics.

Second-harmonic generation of ultrashort pulses in refractive index linearly modulating quantum dot structure

While other works use segments of nonlinear crystal to compensate for walk-off, this work utilizes a quantum dot (QD) nanostructure for such compensation. Such nanocrystal structures allow two benefits: the high nonlinear susceptibility in these nanocrystals and the high surface density of QDs in the structure. Good results are obtained for pre-chirping and modulation parameters. The results are computed at 10 and 100 kV/cm applied electric fields. Compared to ordinary nonlinear crystals, the pulse width, intensity, and efficiency of the second harmonic (SH) pulse are all higher in QD nanocrystals, even with a low electric field applied. Higher applied fields give higher results.

Insight into bay-/end-substituted perylene diimide and its S-scheme heterojunction for enhanced photocatalytic H2O2 production under visible-light irradiation

Here, 1D bis(N-carboxymethyl) peryleneimide (H2PDI), 0D 1,6,7,12-tetrachloro-bis(N-carboxymethyl) peryleneimide (4Cl-H2PDI), and 2D 4Cl-H2PDI/graphene quantum dot (4Cl-H2PDI/GQD) nanostructures are synthesized and carefully analyzed. The effect of bay-/end-substitution and S-scheme heterojunction of PDI-based materials as main catalysts on the photocatalytic H2O2 evolution is first studied through the oxygen reduction reaction (ORR). Under the visible-light irradiation (> 420 nm), 4Cl-H2PDI and 4Cl-H2PDI/GQD as photocatalysts exhibit the ∼7 and ∼16 times H2O2 evolution rate than H2PDI (1059.6 vs. 2484.0 vs. 160.0 µM g−1 h−1), respectively. The systematical experiments reveal that 4Cl-H2PDI and 4Cl-H2PDI/GQD should prefer a two-step single-electron ORR process, while H2PDI may involve a 4e‒ water oxidation and one-step 2e‒ ORR process. Further experiments confirm that the bay-substitution and GQD doping of H2PDI can promote the generation, transportation, and separation of photogenerated electrons and holes, and prolong the carrier lifetime. This work provides insight into PDI-based photocatalytic H2O2 production.

Surface modification of transition metals (TM: Mn, Fe, Co) decorated Pt-doped carbon quantum dots (Pt@CQDs) nanostructure as nonenzymatic sensors for nitrotyrosine (a biomarker for Alzheimer): Perspective from density functional theory

To develop a method for the detection of nitrotyrosine (NTS), transition metals: cobalt (Co), Iron (Fe), and Manganese (Mn) decorated Platinum-doped carbon quantum dot (Pt@CQDs) nanomaterial surfaces were computationally investigated. This study employed density functional theory (DFT) at the d3bj-B3LYP/def2SVP level of theory to gain in-depth knowledge of the adsorption, selectivity, reactivity, and trapping efficacy of nitrotyrosine (NTS) as a biomarker for Alzheimer disease. Results of the adsorption energy of the systems increased as −46.661 kcal/mol, −45.308 kcal/mol, −666.673 kcal/mol, and −12.507 kcal/mol which correspond to NTS_Co_Pt@CQDs, NTS_Fe_Pt@CQDs, NTS_Mn_Pt@CQDs, and NTS_Pt@CQDs. NTS_Mn_Pt@QDs system demonstrated the chemisorption as it has the highest adsorption energy. HOMO-LUMO analysis shows that cobalt decorated surface had the least energy gap of 1.586 eV while interaction with nitrotyrosine a decrease in the energy gap was observed particularly NTS_Pt@CQDs and NTS_Fe_Pt@CQDs exhibiting values of 1.850 eV and 1.665 eV respectively, whereas, Co_Pt@CQDs and Mn_Pt@CQDs systems showed drastic increase in the energy gap to 2.404 eV and 2.719 eV. This collective finding of this study is significant enough to present these systems as potential models for the detection and trapping of nitrotyrosine biomarkers for the diagnosis of Alzheimer's disease.

Two-dimensional realization of electromagnetically induced phase grating in a quantum dot nanostructure

In this paper a novel method for electromagnetically induced phase grating in a quantum dot nanostructure is proposed. The four-level quantum dot nanostructure which is designed by solving the Schrödinger and Poisson equations. By size control of quantum dot and external voltage, one can obtain appropriate energy levels which can be interacted by four-optical fields. In this case, a probe, a two-dimensional standing wave and a driving field simultaneously interact by quantum dot for creation of coherent population trapping. A terahertz (THz) signal can influence the electron population in dark and bright levels, therefore optical susceptibility and transmission spectrum of probe field in the medium can be altered. In the presence of the THz field, the medium becomes phase dependent and this makes more of probe energy transfer to the higher order of the diffraction.

Electromagnetically induced grating in azimuthal dependent three-level quantum dot system

The Fraunhofer diffraction pattern in a three-level quantum dot nanostructure is examined. A probe light, a two-dimensional standing wave field, and a weak signal light are the three optical laser fields that the graphene quantum dot interacts with them. The Fraunhofer diffraction pattern of the probe transmitted light has been addressed under two different coupling situations, including when the weak signal light into an optical vortex beam and a plane wave. The Fraunhofer diffraction pattern becomes symmetric for plane wave coupling light, and the diffracted light can be adjusted by the relative phase between applied lights. However, using the orbital angular momentum of light, it is possible to obtain an asymmetric diffraction pattern for optical light. It has been discovered that in both instances, phase modulation of the probe light’s transmission function allows the probe energy to move from zero order to higher orders.

Finite-Size Effects on Cs3Cu2I5 0D Electronic Nanostructures for Ultraviolet-Emitting Applications

The potential to produce ultraviolet (UV) light-emitting devices has attracted significant interest in interdisciplinary fields, particularly in the use of 0D halide nanostructures due to their straightforward synthesis methods and exceptional efficiency in optoelectronics. Here, we present a systematic study involving nanostructure synthesis and significant changes in the electronic structure caused by finite-size effects. We have focused on the investigation of size effects on the UV-light emitting properties of all-inorganic Cs3Cu2I5 halide. We observe that bulk particles present a pronounced bright-blue emission at 440 nm with a high quantum yield of 80%. Very small quantum dots nanostructures (6–10 nm) reveal a significant shift of the photoluminescence peak down to ∼395 nm, close to the UV-A region, but with a quantum yield reduction of 10%. Surface engineering to obtain very small nanoparticles free from defects at the nanocrystal surface is crucial for maintaining a high quantum efficiency, allowing their use in UV-emitting devices.

Orbital angular momentum induced asymmetric diffraction grating in quantum dot molecule

In this paper, we study the Fraunhofer diffraction pattern in a four-level quantum dot nanostructure. The quantum dot interacts with two weak probe and signal laser fields and two strong coupling lights where one of them is a two-dimensional standing wave field. We study the Fraunhofer diffraction pattern of the transmitted probe light when the coherent driving light becomes plan wave or Laguerre Gaussian (LG) vortex light. We found that by controlling the relative phase of the applied lights and orbital angular momentum (OAM) of LG light, the Fraunhofer diffraction pattern can be controlled and the probe energy transfer from zero order to the higher orders, respectively. Moreover, we realized that by controlling the OAM number of the vortex light the asymmetric diffraction pattern is possible.

Controlling of optical bistability and multistability via two different incoherent processes

In this paper, we investigate the optical bistability (OB) and optical multistability (OM) phenomena for a quantum dot nanostructure via two different mechanisms. The first process is based on the application of the incoherent pumping field while the second one is due to the ratio between the injection and cavity injection rates. We show that the appearance of OB and OM properties in the system depends strongly on the presence of these mechanisms. It is found that OB appears in the presence of both mechanisms, but OM appears only when both mechanisms are present in the system simultaneously. We also study the linear absorption behaviors for the case when OB and OM are observed in the system. It is shown that for the multistable state, the absorption properties of the system are different from the bistable state, which has a strong dependence on incoherent processes.

Phase Dependent Parity Time Symmetry in a quantum dot nanostructure

We present a diamond configuration quantum dots nanostructure trapped in two-dimensional (2D) optical lattices for the investigation of parity time (PT) symmetry. We trap quantum dots in a Gaussian density distribution to examine the PT, non-PT, and anti-PT symmetry in periodic 2D optical lattices. The variation in the relative phase of the optical beams in the quantum dots spectrum indicates either PT, anti-PT, or non-PT symmetry, resulting in an intriguing modulation of imaginary and real refractive index (RI) components. Controlling the appropriate modulation of the RI leads in PT symmetry being controlled by a single parameter, the relative phase of the optical fields. Using detuning and the coupling field of Rabi frequencies, we may determine the state of PT symmetry as well as the direction of field propagation. Coherent control of PT symmetry in 2D quantum dot nanostructure trapped in optical lattices may also have applications in 2D optical devices such as diodes, modulators and photonic transistors.

Emerging Trends of Carbon-Based Quantum Dots: Nanoarchitectonics and Applications.

Carbon-based quantum dots (QDs) have emerged as a fascinating class of advanced materials with a unique combination of optoelectronic, biocompatible, and catalytic characteristics, apt for a plethora of applications ranging from electronic to photoelectrochemical devices. Recent research works have established carbon-based QDs for those frontline applications through improvements in materials design, processing, and device stability. This review broadly presents the recent progress in the synthesis of carbon-based QDs, including carbon QDs, graphene QDs, graphitic carbon nitride QDs and their heterostructures, as well as their salient applications. The synthesis methods of carbon-based QDs are first introduced, followed by an extensive discussion of the dependence of the device performance on the intrinsic properties and nanostructures of carbon-based QDs, aiming to present the general strategies for device designing with optimal performance. Furthermore, diverse applications of carbon-based QDs are presented, with an emphasis on the relationship between band alignment, charge transfer, and performance improvement. Among the applications discussed in this review, much focus is given to photo and electrocatalytic, energy storage and conversion, and bioapplications, which pose a grand challenge for rational materials and device designs. Finally, a summary is presented, and existing challenges and future directions are elaborated.

Modeling of magnesium-decorated graphene quantum dot nanostructure for trapping AsH3, PH3 and NH3 gases.

A magnesium-decorated graphene quantum dot (C24H12-Mg) surface has been examined theoretically using density functional theory (DFT) computations at the ωB97XD/6-311++G(2p,2d) level of theory to determine its sensing capability toward XH3 gases, where X = As, N and P, in four different phases: gas, benzene solvent, ethanol solvent and water. This research was carried out in different phases in order to predict the best possible phase for the adsorption of the toxic gases. Analysis of the electronic properties shows that in the different phases the energy gap follows the order NH3@C24H12-Mg < PH3@C24H12-Mg < AsH3@C24H12-Mg. The results obtained from the adsorption studies show that all the calculated adsorption energies are negative, indicating that the nature of the adsorption is chemisorption. The adsorption energies can be arranged in an increasing trend of NH3@C24H12-Mg < PH3@C24H12-Mg < AsH3@C24H12-Mg. The best adsorption performance was noted in the gas phase compared to the other studied counterparts. The interaction between the adsorbed gases and the surfaces shows a non-covalent interaction nature, as confirmed by the quantum theory of atoms-in-molecules (QTAIM) and non-covalent interactions (NCI) analysis. The overall results suggest that we can infer that the surface of the magnesium-decorated graphene quantum dot C24H12-Mg is more efficient for sensing the gas AsH3 than PH3 and NH3.

Separating the Effects of Nonorthogonal Variables on the Hot-Injection Synthesis of Core/Thick-Shell (“Giant”) CdTe/CdS Quantum Dots

“Giant” core/thick-shell quantum dot (QD) nanostructures are of interest due to their unusual optical properties and importance as components of more advanced heterostructures tailored to achieve increasingly complex optical functions. However, reliable one-step seeded growth of these structures poses a significant challenge: one must balance multiple competing reaction processes to find the growth regime that realizes spherical shells of both the target size and high crystalline quality. Adjusting synthesis conditions in thicker-shelled reactions is further complicated by multiple nonorthogonal variables that impact the reaction mechanism. These variables include the reaction volume, reaction concentration, and oleic acid (ligand) concentration. Here, we investigate the seeded growth of core/thick-shell CdTe/CdS QDs by adapting a “flash” shelling method. We systematically vary three key reaction parameters (particle concentration, oleic acid:Cd ratio, and Cd–S:CdTe core ratio) over 30+ different thick-shelling reactions to elucidate the separate and intersecting impacts of these parameters on shell growth. Our analysis of the resulting particle quality reveals that the particle concentration of the reaction plays a critical role in the shell growth mechanism. We find the impact of oleic acid to be dependent on the particle concentration for a given shell thickness. We also find that the optimal conditions shift when targeting increasingly thick shells. The results demonstrate the importance of testing and controlling for synthesis variables across a multidimensional parameter space. We develop and present general experimental design criteria to help guide efficient development of new seeded growth reactions that enable reliable synthesis of thick-shelled nanostructures.

Study of the type-I to type-II band alignment transition in InAs(Sb)/GaAs quantum dot nanostructures

InAs(Sb)/GaAs self-assembled quantum dots (QDs) were grown by molecular beam epitaxy though incorporating Sb into InAs with increased beam equivalent pressure ratio, x = Sb2/(Sb2+As2), of x = 0, 0.15, 0.25, and 0.5. From photoluminescence measurements, we observed a transition of the band alignment from type-I for the InAs QDs to type-II for InAsSb QDs. Thus, after adding Sb into the QDs these type II InAsSb QDs have different characteristics from the well-studied type-I InAs QDs regarding to their excitation intensity dependence, temperature dependence, and time dependence of the luminescence. Additionally, the Sb distribution in the QDs and the wetting layer was studied. These results indicate that we are able to fabricate InAsSb QDs with a type II band alignment, which may be good optical materials for the development of intermediate-band photovoltaic cells.

Nanostructure–Optical Property Relationship in CuInSe2/ZnS Core/Shell Quantum Dots Revealed by Multivariate Statistical Analysis of X-ray Spectrum Images

Modifying nanostructures of colloidal quantum dots (QDs), such as forming core/shell structures and alloying, is a common strategy for tuning their optical properties. However, the relationship between the actual nanostructures and optical properties of QDs remains poorly discussed owing to inherent difficulties in the structural analysis of QDs. Here, we investigated nanostructures of CuInSe2/ZnS core/shell QDs as a function of temperature during ZnS shell growth using X-ray energy-dispersive spectroscopy spectrum imaging combined with multivariate statistical analysis. Lower signal-to-noise ratios resulting from very weak characteristic X-rays emitted from QDs were overcome using an aberration-corrected transmission electron microscope equipped with a large solid-angle X-ray detection system (total solid angle of 1.6 sr). The nanoscale X-ray mapping elucidated that QDs with homogeneous cores and island-like shells surrounding core vertexes were formed at temperatures of 225 and 250 °C. Moreover, diffusion of Zn atoms from shells to cores was revealed by quantitative analysis of the core composition and verified by atomic diffusion simulations. These modified nanostructures should contribute to the decrease in surface traps and internal defects, enhancing the optical properties of QDs. The nanoscale X-ray mapping provides direct evidence of modified nanostructures of QDs.

Impact of Applied Temperature and Hydrostatic Pressure on the Off-Center Donor Spectrum in Spherical Quantum Dot

Within the effective mass approximation and the infinite confinement potential, this work focused on studying the electronic properties of spherical quantum dot (SQD) nanostructure through the finite difference method. The effects of shallow donor impurity position, temperature (T), and hydrostatic pressure (P) on the binding energy, the electron spatial extension &lt;re&gt; and the average electron-impurity distance &lt;rD-e&gt; in a SQD have been evaluated. Our findings show that the binding energy increases as a function of hydrostatic pressure and decreases with the temperature effect. However, the binding energy presents very clear maximum around the spherical nanostructure center depending on the impurity position. For higher SQD, the impact of externals perturbations (P and T) on the electron spatial extension are more significant. The distance &lt;re&gt; decreases with the augmentation of hydrostatic pressure when the impurity is near the center, which is conversely when the impurity is near the edge. In addition, applying the hydrostatic pressure and temperature leads to decreasing and increasing the average distance &lt;rD-e&gt;, respectively.

Phase control of optical Goos–Hänchen shifts in a quantum dot nanostructure via high refractive index

We proposed a model for adjusting Goos–Hänchen (GH) shifts in a cavity with quantum dot (QD) nanostructure in this letter. The actual component of the susceptibility was studied by analytical solution of the coherence term of the density matrix elements, and the refractive index of the QD nanostructure was explored. We discovered that the intracavity medium became phase sensitive because of the electron tunneling action. As a result, the relative phase of applied lights may be used to manipulate the medium’s refraction index. The GH shifts in reflected and transmitted light beams in high refractive index QD nanostructures with diminishing probe absorption were next examined. We discovered that the GH shifts of reflected and transmitted lights are greatly influenced by the applied lights’ relative phase. We established that greater negative or positive GH shifts in reflected and transmitted photons are conceivable in the presence of electron tunneling.

Absorption Enhancement in a Quantum Dot Thz Detector with a Metal-Semiconductor-Metal Structure

The low absorptivity of quantum dot nano-structures cannot meet the requirements for high-performance next-generation Thz detectors which can be used for environmental pollution detection. In this study, a novel metal-semiconductor-metal (MSM) cavity structure with a square hole array instead of a traditional planar metal electrode was developed to improve and enhance the absorptivity of a quantum dot Thz detector. The possible modes and loss problems in the metal resonant cavity were analyzed using the finite-element transmission matrix, the eigenvector method, and Kirchhoff diffraction theory. The results demonstrate that the MSM cavity structure introduced in the detector can enhance absorption up to 8.666 times higher than that of the conventional counterpart.