Quantum Confinement Research Articles

Novel Synthesis and Biophysical Characterization of Zinc Oxide Nanoparticles Using Virgin Coconut Oil.

One of the primary concerns in the field of green synthesis of nanoparticles (NPs) utilizing plant materials is the scarcity of high purity, challenges in achieving large-scale production, and limited global accessibility. Hygienic preparation and safe storage of plant extracts are also considerable challenges in this field. So, an investigation was started to overcome these limitations. Virgin coconut oil (VCO) in its purest form is available commercially all over the world. Also, it has high medicinal value with excellent biomedical applications. Very limited work has been reported on oils as bio reducers and stabilizers. In those reports, they used a few chemicals as mediators in the processes of synthesis and cleaning. So, to the best of our knowledge, for the first time, zinc oxide (ZnO) NPs were synthesized using VCO as a reducing and capping agent with zero chemical mediators. A comprehensive investigation of the structural, microstructural, and optical properties was reported. X-ray diffraction confirms the formation of VCO-ZnO NPs with an average crystallite size of 32.81 nm in a hexagonal structure. UV characteristics confirm quantum confinement through a well-defined SPR near 223 nm with fwhm of 67 nm and a direct band gap at 3.96 eV. FTIR reveals the capping of VCO through carboxylic functional groups, particularly the -COO- group of coconut oil at 1770 cm-1 with a shift of about 30 cm-1 compared to plain VCO. TEM confirms the polycrystalline nature with nearly spherical and 10-22 nm particle size. The zeta potential of -15.4 ± 5.0 mV signifies the stability and antiagglomeration properties. FESEM with EDS results confirms morphological excellence, the purity level of synthesized NPs (99.5%), and the prominent scalability of NPs (84.38% yield). Finally, as-synthesized VCO-ZnO NPs showed very good antioxidant (IC50 78.991, 51.464, and 4.677 μg/mL in DPPH, ABTS, and FRAP assays, respectively), anti-inflammatory (IC50 22.42 μg/mL in protein denaturation), antimicrobial (MIC 0.156 mg/mL for Pseudomonas and 0.316 mg/mL for S. aureus), and antidiabetic properties (IC50 88.45 and 147.67 μg/mL for α-amylase and α-glucosidase assays, respectively).

Two-dimensional vortex dipole, tripole, and quadrupole solitons in nonlocal nonlinearity with Gaussian potential well and barrier

Two-dimensional vortex dipole, tripole, and quadrupole solitons in nonlocal nonlinearity with Gaussian potential well and barrier

Hybrid Eu(II)-bromide scintillators with efficient 5d-4f bandgap transition for X-ray imaging

Luminescent metal halides are attracting growing attention as scintillators for X-ray imaging in safety inspection, medical diagnosis, etc. Here we present brand-new hybrid Eu(II)-bromide scintillators, 1D type [Et4N]EuBr3·MeOH and 0D type [Me4N]6Eu5Br16·MeOH, with spin-allowed 5d-4f bandgap transition emission toward simplified carrier transport during scintillation process. The 1D/0D structures with edge/face -sharing [EuBr6]4− octahedra further contribute to lowing bandgaps and enhancing quantum confinement effect, enabling efficient scintillation performance (light yield ~73100 ± 800 Ph MeV−1, detect limit ~18.6 nGy s−1, X-ray afterglow ~ 1% @ 9.6 μs). We demonstrate the X-ray imaging with 27.3 lp mm−1 resolution by embedding Eu(II)-based scintillators into AAO film. Our results create the new family of low-dimensional rare-earth-based halides for scintillation and related optoelectronic applications.

Intrinsic performance limits of extremely scaled field-effect transistors based on MX2 (M = {Zr, Hf}, X = {S, Se}) nanoribbons

We investigate the MX2 (M = {Hf, Zr}, X = {S, Se}) transition metal dichalcogenides patterned into armchair (AC) and zigzag (ZZ) nanoribbons (NRs) as potential channel materials in future logic field-effect devices. Ab initio quantum transport simulations are employed to assess the electronic, transport, and ballistic field-effect transistor (FET) properties of devices with such quasi-one-dimensional channels. We report a non-monotonic scaling behavior of MX2NR properties due to strong quantum confinement effects, which is reflected in a strong dependence of the ON-state current (ION) of MX2NR FETs on the nanoribbon configuration. The ∼2 nm-wide HfSe2 and ZrSe2 AC-PFETs have the highest ION of up to 2.6 mA/μm at 10 nA/μm OFF-state current. Surprisingly, MX2NR ZZ-NFETs exhibit a current increase of up to 70% when channel width is scaled down, with ION reaching 2.2 mA/μm in ∼2 nm-wide devices. The high ON-state performance is a direct consequence of high carrier injection velocity, which is explained by analyzing the band structure, transmission, and density of states. We demonstrate that nanostructured MX2 materials can be promising candidates for future logic transistors based on multi-nanowire architectures.

Excitonic optical properties in monolayer SnP2S6

Abstract Quantum confinement effect and reduced dielectric screening in two-dimensional (2D) dramatically enhance the electron–hole interactions. In this work, we use many-body perturbation theory and Bethe–Salpeter equation (BSE) to investigate the electronic and excitonic optical properties of monolayer SnP2S6. Our findings reveal that the excitonic effect dominates the optical absorption spectra in the visible light range, and the lowest-energy exciton X 0 in monolayer SnP2S6 is optically bright with the binding energy of 0.87 eV and the radiative lifetime of ∼ 10−11 s, which is highly advantageous to the photo-luminescence. Most importantly, the absence of optically forbidden states below the bright states X 0 would give rise to a high quantum efficiency of 2D SnP2S6. We also find that applied biaxial strain can further shorten the radiative lifetime of the bright states. These results imply that 2D SnP2S6 is a promising candidate for the optoelectronic devices.

Impacts of quantum confinement effect on threshold voltage and drain-induced barrier lowering effect of junctionless surrounding-gate nanosheet NMOSFET including source/drain depletion regions

In order to modeling of junctionless (JL) surrounding-gate (SG) nanosheet MOSFET more accurately, a new model for determining threshold voltage and drain-induced barrier lowering (DIBL) effect of JL SG nanosheet NMOSFET is proposed through deriving the Poisson's equation under rectangular coordinate system. The model captures quantum confinement effect and source/drain depletion regions, it is validated through the Sentaurus TCAD simulation results. Variations of source/drain depletion regions with the channel width, height, doping concentration, the gate bias, the drain bias and variations of threshold voltage, DIBL with the channel width, height, doping concentration considering and not considering quantum confinement effect are studied, respectively. The results show influences of quantum confinement effect on source/drain depletion regions, threshold voltage and DIBL. The developed model will offer quantum corrections in JL SG nanosheet NMOSFET.

Inverted V-shaped size-dependent emission wavelength shift in InGaN micro-LEDs with size down to 1 μm

The size-dependent emission wavelength shift of micro-scale light emitting diodes (micro-LEDs) has been frequently reported in recent publications, but its underlying physical mechanism has not yet been thoroughly elucidated. Here, we fabricate and characterize the red, green, and blue InGaN micro-LED mesas with different diameters down to 1 μm. As the size decreases, all the samples of different colors show an inverted V-shaped photoluminescence wavelength variation trend, first a red shift and then a blue shift, and the shifting range is larger for samples with longer wavelengths. Micro-Raman spectrum confirms that the stress was significantly released after scaling down the size from epitaxial wafer to 1 μm. The theoretical simulations show that the red and blue shifts are, respectively, attributed to the bandgap narrowing and the weakening of the quantum-confined Stark effect caused by strain relaxation, which dominate successively.

A Futuristic Development in 3D Printing Technique Using Nanomaterials with a Step Toward 4D Printing.

3D bioprinting has shown great promise in tissue engineering and regenerative medicine for creating patient-specific tissue scaffolds and medicinal devices. The quickness, accurate imaging, and design targeting of this emerging technology have excited biomedical engineers and translational medicine researchers. Recently, scaffolds made from 3D bioprinted tissue have become more clinically effective due to nanomaterials and nanotechnology. Because of quantum confinement effects and high surface area/volume ratios, nanomaterials and nanotechnological techniques have unique physical, chemical, and biological features. The use of nanomaterials and 3D bioprinting has led to scaffolds with improved physicochemical and biological properties. Nanotechnology and nanomaterials affect 3D bioprinted tissue engineered scaffolds for regenerative medicine and tissue engineering. Biomaterials and cells that respond to stimuli change the structural shape in 4D bioprinting. With such dynamic designs, tissue architecture can change morphologically. New 4D bioprinting techniques will aid in bioactuation, biorobotics, and biosensing. The potential of 4D bioprinting in biomedical technologies is also discussed in this article.

Properties of V-defect injectors in long wavelength GaN LEDs studied by near-field electro- and photoluminescence

The efficiency of multiple quantum well (QW) light emitting diodes (LEDs) to a large degree depends on uniformity of hole distribution between the QWs. Typically, transport between the QWs takes place via carrier capture into and thermionic emission out of the QWs. In InGaN/GaN QWs, the thermionic hole transport is hindered by the high quantum confinement and polarization barriers. To overcome this drawback, hole injection through semipolar QWs located at sidewalls of V-defects had been proposed. However, in the case of the V-defect injection, strong lateral emission variations take place. In this work, we explore the nature of these variations and the impact of the V-defects on the emission spectra and carrier dynamics. The study was performed by mapping electroluminescence (EL) and photoluminescence (PL) with a scanning near-field optical microscope in LEDs that contain a deeper well that can only be populated by holes through the V-defects. Applying different excitation schemes (electrical injection and optical excitation in the far- and near-field), we have shown that the EL intensity variations are caused by the lateral nonuniformity of the hole injection. We have also found that, in biased structures, the PL intensity and decay time in the V-defect regions are only moderately lower that in the V-defect-free regions thus showing no evidence of an efficient Shockley-–Read–Hall recombination. In the V-defect regions, the emission spectra experience a red shift and increased broadening, which suggests an increase of the In content and well width in the polar QWs close to the V-defects.

Effect of stability state transition of variable potential well in tri-hybridized energy harvesters

Energy harvesting is a crucial technology for self-powering wireless sensor nodes and mobile terminals. In addressing this, we utilized a variable potential well to create a tri-hybrid energy harvester that integrates piezoelectric effect, electromagnetic induction, and triboelectric effect. The compression and stretching of a compressible magnet-spring oscillator alter the system’s potential well, thereby promoting the operation of the piezoelectric unit (PU), electromagnetic unit (EU), and triboelectric unit (TU). A coupled electromechanical model using Hamilton’s principle was established. By calculating the static potential energy and restoring force, we discussed the stability state transition, revealing that when the magnet distance is less than 38 mm, the system transitions from a mono-stable to a bi-stable state. The experimental study investigated the impact of excitation and structural parameters on voltage and power. A high excitation level enhances all three units. The TU demonstrates excellent electrical performance under high potential energy in the bi-stable state, while the PU performs best in mono- and bi-stable switching structure. The EU shows relatively balanced electrical performance across various conditions. These findings offer new insights into enhancing energy harvesting capabilities for external circuits.

Semiclassical Quantization Conditions in Strained Moiré Lattices

In this article we generalize the Bohr–Sommerfeld rule for scalar symbols at a potential well to matrix-valued symbols having eigenvalues that may coalesce precisely at the bottom of the well. As an application, we study the existence of approximately flat bands in moiré heterostructures such as strained two-dimensional honeycomb lattices in a model recently introduced by Timmel and Mele.

A priori estimates and existence of positive stationary solutions for semilinear parabolic equations

We study the boundedness of global solutions to the semilinear parabolic equations with combined nonlinearities. Firstly, we establish a sufficient condition for the initial data using the potential well method, ensuring the global existence of solutions. Subsequently, we proceed to demonstrate an a priori estimate for all global solutions. Finally, the potential well theory, in conjunction with the derived a priori estimate, we show that there is a sub-convergent sequence of the global flow, which converges the positive solution to the corresponding stationary equation.

Enhancement of pair production in oscillated overlapped fields

The electron-positron pair production has been investigated in two overlapped potential wells with varied widths and frequencies. Notably, specific multiphoton absorption processes exhibit distinct changes, the total number of created pairs increases linearly, and appears in periodic oscillation with the spatial extends of the potential wells. Furthermore, the investigation revealed the crucial impact of the smaller frequency on the pair production yield. The optimal combination of frequencies was determined to enhance the creation of pairs in overlapped fields. These findings provide valuable insights into the dynamics of multiphoton absorption processes and offer a pathway toward maximizing pair creation in complex potential landscapes. Published by the American Physical Society 2024

Multiplicity and concentration of nontrivial solutions for Kirchhoff–Schrödinger–Poisson system with steep potential well

Multiplicity and concentration of nontrivial solutions for Kirchhoff–Schrödinger–Poisson system with steep potential well

Analysis of candidate oil wells for workover interventions using machine learning tools

Throughout their production life oil wells have the potential to undergo workover interventions with one of the possible objectives to maintain healthy production levels. In mature fields, generally in a declining production stage, increases the need of evaluations and monitoring of the flow levels of productive fluids, to indicate those who are producing below their potential. In this context, a study case was conducted to analyze operational parameters associated with well production fluids by applying data science tools, considering the premise all are intact in terms of safety barriers. Starting from the selection of interest variables and data collection, an exploratory analysis was initially proposed to examine the interrelations between variables. For the identification of patterns and well groupings, two machine learning techniques were applied: Principal Component Analysis (PCA) and Cluster Analysis. PCA allowed the reduction of the variable set dimensionality, facilitating a practical visualization of each well’s productive scenario based on the analysis of the three selected principal components. Furthermore, through Cluster Analysis, wells were categorized into five distinct Clusters, enhancing the monitoring and management of potential candidate wells.

Electrical properties enhancement of dually grafting modification for polypropylene cable insulation

AbstractPolypropylene (PP) is believed to be a rather promising cable insulating material for high‐capacity electric power system with low carbon emission due to its decent thermo‐resistance and recyclable nature. In this paper, a new dually chemical grafting modification strategy by methyl acrylate (MA) and acrylic acid (AA) is put forward to tailor the charge transportation behavior in PP, thus further enhancing the electrical properties. Experimental results indicate that the dually grafted PP with 2.3 weight percent (wt%) MA and 1.9 wt% AA shows enhanced volume resistivity and electrical breakdown strength than pure PP, and the space charge injection is significantly suppressed. This work further adopts thermally stimulated depolarization current (TSDC) test and computational analysis based on density functional theory (DFT) to reveal the mechanism of enhancement. The analysis shows that grafted chemical groups can introduce quantities of deep traps and electrostatic potential wells which are strongly correlated with the carbonyl group and would hinder the charge transportation thus improving the electrical insulating performances of PP. This work would provide a new route of PP‐based dually grafting modification for the development of high‐voltage cable insulation.

Strong Dipole Moments from Ferrocene Methanol Clusters Boost Exciton Dissociation in Quantum-Confined Perovskite for CO2 Photoreduction.

Perovskite nanocrystals (PCNs) exhibit a significant quantum confinement effect that enhances multiexciton generation, making them promising for photocatalytic CO2 reduction. However, their conversion efficiency is hindered by poor exciton dissociation. To address this, we synthesized ferrocene-methanol-functionalized CsPbBr3 (CPB/FcMeOH) using a ligand engineering approach. By manipulating the electronic coupling between ligands and the PCN surface, facilitated by the increased dipole moment from hydrogen bonding in FcMeOH molecules, we effectively controlled exciton dissociation and interfacial charge transfer. Under 5 h of irradiation, the CO yield of CPB/FcMeOH reached 772.79 μmol g-1, 4.95 times higher than pristine CPB. This high activity is due to the formation of hydrogen-bonded FcMeOH clusters on the CPB surface. The nonpolar disruption and strong dipole moment of FcMeOH molecules enhance electronic coupling between the FcMeOH ligands and the CPB surface, reducing the surface barrier energy. Consequently, exciton dissociation and interfacial charge transfer are promoted, efficiently utilizing multiple excitons in quantum-confined domains. Transient absorption spectroscopy confirms that CPB/FcMeOH exhibits optimized exciton behavior with fast internal relaxation, trapping, and a short recombination time, allowing photogenerated charges to more rapidly participate in CO2 reduction.

Impact of using dual back surface field layers of different materials on GaAs single junction solar cell performance

This research aspires to investigate the impact of employing dual BSF layers on the performance of single junction GaAs solar cells using the Silvaco TCAD simulator. A layer of GaAs, InGaP, and InAlGaP has been implemented as a second BSF layer on top of the original BSF layer of the n-InGaP/n-GaAs/p-GaAs/p-InAlGaP structured solar cell. The results show that using GaAs as a second BSF layer has increased the carrier’s recombination and degraded the cell efficiency due to its lower energy bandgap, which creates a potential well that lessens the number of photogenerated carriers flowing through the conduction band toward electrodes. However, adding InGaP and InAlGaP as a second BSF layer decreases the recombination rate and generates a broad electric field region leading to extra photogenerated carriers drifting through the cell, which increases the efficiency from 29.42% to 29.81% for the case of using InGaP and 30.33% for the case of using InAlGaP. Furthermore, increasing the thickness and doping of the second BSF layer reduces the carriers’ recombination at the boundaries of this layer, which implies efficiency enhancement.

Quantum-Confined Lifshitz Transition on Weyl Semimetal Td-MoTe2.

Adsorption of alkali atoms onto material surfaces is widely utilized for controlling electronic properties and is particularly effective for two-dimensional materials. While tuning the chemical potential and band gap and creating quantum-confined states are well established for alkali adsorption on semiconductors, the effects on semimetallic systems remain largely elusive. Here, utilizing angle-resolved photoemission spectroscopy measurements and density functional theory calculations, we disclose the creation of two-dimensional electron gas and the quantum-confined Lifshitz transition at the surface of a Weyl semimetal Td-MoTe2 by potassium adsorption. Electrons from potassium adatoms are shown to be transferred mainly to the lowest unoccupied band within the gapped part of the Brillouin zone, which, in turn, induces strong surface band bending and quantum confinement in the topmost layer. The quantum-confined topmost layer evolves from a semimetal to a strong metal with a Lifshitz transition departing substantially from the bulk band. The present finding and its underlying mechanism can be exploited for the creation of electronic heterojunctions in van der Waals semimetals.

The effect of quantum confinement and the role of electron-phonon interaction on the band gap shrinkage of some II-VI semiconductors

The role of electron-phonon interaction in band gap shrinkage for some II-VI bulk and low-dimensional semiconductors is investigated in this work. The variation of the energy band gap is studied as a function of temperature using Varshni's, Vina's, and Passler's relations. It is observed that the change in the energy band gap is affected due to the quantum confinement as the dimensionality of these semiconductors is decreased.