Confinement Energy Research Articles

Influence of carrier localization on photoluminescence emission from sub-monolayer quantum dot layers

We have investigated the origins of photoluminescence from quantum dot (QD) layers prepared by alternating depositions of sub-monolayers and a few monolayers of size-mismatched species, termed as sub-monolayer (SML) epitaxy, in comparison with their Stranski–Krastanov (SK) QD counterparts. Using measured nanostructure sizes and local In-compositions from local-electrode atom probe tomography as input into self-consistent Schrödinger–Poisson simulations, we compute the 3D confinement energies, probability densities, and photoluminescence (PL) spectra for both InAs/GaAs SML- and SK-QD layers. A comparison of the computed and measured PL spectra suggests one-dimensional electron confinement, with significant 3D hole localization in the SML-QD layers that contribute to their enhanced PL efficiency in comparison to their SK-QD counterparts.

Quantum migration and its local heat impact: Understanding local heat capacity of confined systems.

For noninteracting particles confined in a constant volume, the temperature derivative of the local energy assumes negative values in thermodynamic equilibrium at low temperatures. This peculiar behavior may entail the misleading unphysical conclusion that the local heat capacity is negative. However, we show that temperature-dependent density variations of confined particles induce an energy selective particle transport within the domain, here called temperature-induced quantum migration. This macroscopic quantum phenomenon causes a redistribution of local heat and ensures a non-negative local heat capacity. Moreover, it induces local heating and cooling effects and a massive overshoot in local heat capacity. The quantum migration also builds up the thermal part of confinement energy, manifesting in an excess global heat capacity. Analyzing the local energy fluctuations shows that the linear relationship between heat capacity and fluctuations is broken at the local scale.

Confinement energy landscape classification reveals membrane receptor nano-organization mechanisms

The cell membrane organization has an essential functional role through the control of membrane receptor confinement in micro- or nanodomains. Several mechanisms have been proposed to account for these properties, although some features have remained controversial, notably the nature, size, and stability of cholesterol- and sphingolipid-rich domains or lipid rafts. Here, we probed the effective energy landscape acting on single-nanoparticle-labeled membrane receptors confined in raft nanodomains— epidermal growth factor receptor (EGFR), Clostridium perfringens ε-toxin receptor (CPεTR), and Clostridium septicum α-toxin receptor (CSαTR)—and compared it with hop-diffusing transferrin receptors. By establishing a new analysis pipeline combining Bayesian inference, decision trees, and clustering approaches, we systematically classified single-protein trajectories according to the type of effective confining energy landscape. This revealed the existence of only two distinct organization modalities: confinement in a quadratic energy landscape for EGFR, CPεTR, and CSαTR (A), and free diffusion in confinement domains resulting from the steric hindrance due to F-actin barriers for transferrin receptor (B).The further characterization of effective confinement energy landscapes by Bayesian inference revealed the role of interactions with the domain environment in cholesterol- and sphingolipid-rich domains with (EGFR) or without (CPεTR and CSαTR) interactions with F-actin to regulate the confinement energy depth. These two distinct mechanisms result in the same organization type (A). We revealed that the apparent domain sizes for these receptor trajectories resulted from Brownian exploration of the energy landscape in a steady-state-like regime at a common effective temperature, independently of the underlying molecular mechanisms. These results highlight that confinement domains may be adequately described as interaction hotspots rather than rafts with abrupt domain boundaries. Altogether, these results support a new model for functional receptor confinement in membrane nanodomains and pave the way to the constitution of an atlas of membrane protein organization.

Evidence of two-dimensional lateral quantum confinement in self-formed core–shell InGaN nanowires on Si (111) emitting in the red

The proof of strong two-dimensional lateral quantum confinement in the In-rich core of red-light emitting self-formed core–shell InGaN nanowires is given. The nanowires are directly grown on Si (111) by plasma-assisted molecular beam epitaxy. After the initial InGaN nucleation, straight nanowires with quantum-size core radius determined by x-ray diffraction, transmission electron microscopy, and energy dispersive x-ray mappings develop. Detailed comparison of the photoluminescence from the core, the In contents of the core and shell, and the core radius with theoretical modeling reveals a parabolic confinement potential with large ground state quantum confinement energies of electrons and holes. Such strong lateral quantum confinement in a vertical quantum wire active region is ideal for the performance of optoelectronic devices, in particular of our reported red InGaN light emitting diode with high brightness and color stability.

Gas Uptake and Thermodynamics in Porous Liquids Elucidated by 129Xe NMR.

We exploited 129Xe NMR to investigate xenon gas uptake and dynamics in a porous liquid formed by dissolving porous organic cages in a cavity-excluded solvent. Quantitative 129Xe NMR shows that when the amount of xenon added to the sample is lower than the amount of cages present (subsaturation), the porous liquid absorbs almost all xenon atoms from the gas phase, with 30% of the cages occupied with a Xe atom. A simple two-site exchange model enables an estimate of the chemical shift of 129Xe in the cages, which is in good agreement with the value provided by first-principles modeling. T2 relaxation times allow the determination of the exchange rate of Xe between the solvent and cage sites as well as the activation energies of the exchange. The 129Xe NMR analysis also enables determination of the free energy of confinement, and it shows that Xe binding is predominantly enthalpy-driven.

Influence of the DEA Concentration on Structural and Optical Properties of Nanodot PbS Thin Films Growth by Chemical Solution Deposition: Unveiling Dual Optical Absorption Edges

The present paper presents a straightforward method for producing thin film layers of sulfide quantum dots (PbS-QDs) on a glass substrate using chemical solution deposition (CSD) assisted by dipcoating technique. The deposited PbS-QDs films were subjected to a comprehensive analysis using atomic force microscopy (AFM), energy dispersive X-ray (EDX) scanning electron microscopy (SEM), X-ray diffraction (XRD), UV–vis–IR absorption, and photoluminescence spectroscopic (PL) techniques to investigate the effects of varying concentrations of diethanol amine (DEA) on their morphology, crystal structure, elemental composition, light absorption, and emission characteristics. The spherical shape of the PbS-QDs was confirmed by AFM and SEM images with average sizes around 100 and 50 nm, respectively. The energy dispersive X-ray (EDX) analysis provides evidence the existence of Pb and S elements within the PbS matrix. X-ray diffraction (XRD) results validate that the deposited films exhibit high crystallinity, with a preferential orientation along the (111) plane and a face-centered cubic lattice structure of PbS. The crystallite size of PbS is measured to be 46.6 nm. Based on the optical absorption measurements, we have determined the size range of PbS nanocrystals to be between 4.3 and 11.5 nm. The optical studies reveal the presence of two optical absorption edges within the visible and infrared spectrum, two direct band gap energy, two cut-off wavelengths, two confinement energy, two Urbach energy tail, and dual emission peaks of PbS-QDs at room temperature. The analysis reveals the presence of two distinct band gap energies, one in the visible range (1.3–2.28 eV) and the other in the infrared range (0.65–0.88 eV), which can be attributed to the formation of two distinct sizes of quantum dots situated in two different layers. The first layer, deposited directly on the glass substrate, comprises quantum dots with an average size of approximately 5.2 nm, while the second layer contains quantum dots with an average size of about 9.5 nm. This ability to tune the band gap of PbS in the visible range up to the IR band (0.65–2.28 eV) is a critical feature that holds the potential for the development of innovative optoelectronic devices.

Controllable quantum scars induced by spin–orbit couplings in quantum dots

Spin–orbit couplings (SOCs), originating from the relativistic corrections in the Dirac equation, offer nonlinearity in the classical limit and are capable of driving chaotic dynamics. In a nanoscale quantum dot confined by a two-dimensional parabolic potential with SOCs, various quantum scar states emerge quasi-periodically in the eigenstates of the system, when the ratio of confinement energies in the two directions is nearly commensurable. The scars, displaying both quantum interference and classical trajectory features on the electron density, due to relativistic effects, serve as a bridge between the classical and quantum behaviors of the system. When the strengths of Rashba and Dresselhaus SOCs are identical, the chaos in the classical limit is eliminated as the classical Hamilton’s equations become linear, leading to the disappearance of all quantum scar states. Importantly, the quantum scars induced by SOCs are robust against small perturbations of system parameters. With precise control achievable through external gating, the quantum scar induced by Rashba SOC is fully controllable and detectable.

Swelling and deswelling driven multimaterials silicone hopper with superior specific power and energy

Bioinspired, bistable snap-through structures are promising to release a burst of mechanical energy transformed from chemical energy, stored, and released incrementally during swelling/deswelling. Thin, disk-like hopper can harness the inhomogeneous deswelling to create the required constraint and flexible snap-through part. Here, hoppers composed of a single type of polydimethylsiloxane (PDMS) or concentric PDMS rimmed by a stiffer PDMS are cast into precisely micromachined molds. The mechanical properties and swelling/deswelling behavior of the constraining rim and flexible snap-through materials, in concert, allow a superior specific power of 1782 W kg−1, specific energy of 4.44 J kg−1 for a jump up to 321 mm, outperforming many more complex implementations. The jump benefits from an improved storage modulus ratio and a lower swell of the rim to the snap-through center part, which enhanced the confinement and elastic energy storage. A sharp spatial gradient in volume change between the two materials during deswelling, tunable by the porosity of the rim materials, enhances the jumping by allowing more material to store and release elastic energy, revealed by the strain analysis with 3D-digital image correlation. The illustrated multimaterials and porous materials strategies can promote the development of integrated energy harvesting and actuation for soft robotics.

Direct Observation of Circularly Polarized Nonlinear Optical Activities in Chiral Hybrid Lead Halides.

Circularly polarized light emission is a crucial application in imaging, sensing, and photonics. However, utilizing low-energy photons to excite materials, as opposed to high-energy light excitation, can facilitate deep-tissue imaging and sensing applications. The challenge lies in finding materials capable of directly generating circularly polarized nonlinear optical effects. In this study, we introduce a chiral hybrid lead halide (CHLH) material system, R/S-DPEDPb3Br8·H2O (DPED = 1,2-diphenylethylenediammonium), which can directly produce circularly polarized second harmonic generation (CP-SHG) through linearly polarized infrared light excitation, exhibiting a polarization efficiency as high as 37% at room temperature. To understand the spin relaxation mechanisms behind the high polarization efficiency, we utilized two models, so-called D'yakonov-Perel' (DP) and Bir-Aronov-Pikus (BAP) mechanisms. The unique zigzag inorganic frameworks within the hybrid structure are believed to reduce the dielectric confinement and exciton binding energy, thus enhancing spin polarization, especially in regions with a high excitation pump fluence based on the DP mechanism. In the case of low excitation pump fluence, the BAP mechanism dominates, as evidenced by the observed decrease in the polarization ratio from CP-SHG measurement. Using density functional theory analysis, we elucidate how the distinctive 8-coordination environment of lead bromide building blocks effectively suppresses spin-orbit coupling at the conduction band minimum. This suppression significantly diminishes spin-splitting, thereby slowing the spin relaxation rate.

Stop Blaming Hopping Conduction in Nanocrystal Arrays, Use it for Active Photonics!

AbstractNanocrystals (NCs) are now established building blocks for photonic applications. However, their integration for optoelectronics has not yet reached the same level of maturity, in part due to the perceived bottleneck that is the inherent limited mobility resulting from hopping conduction. Significant efforts are made to improve this mobility, notably by tuning the particle surface chemistry to enable larger interparticle electronic coupling, and values of mobility of ≈10 cm2 V−1 s−1 have been achieved. It is acknowledged that this value remains significantly lower than those obtained in 2D electron gases but is on par with the mobility reported for vertical transport in epitaxially grown heterostructures with similar confinement energies. Since there appears to be limited perspectives for further increasing mobility values, a suggestion is made that efforts should instead be directed toward exploring the potential benefits offered by hopping conduction. One of these benefits is the bias dependence of the diffusion length, which plays a key role in designing bias‐reconfigurable optical responses for NC‐based devices. Some recent achievements in building bias‐activated devices will be reviewed and the essential criteria for designing future structures will be discussed. Ultimately, hopping conduction is an opportunity to generate new functionalities that low‐disorder materials would be unable to provide.

Efficiency of InN/InGaN/GaN Intermediate-Band Solar Cell under the Effects of Hydrostatic Pressure, In-Compositions, Built-in-Electric Field, Confinement, and Thickness.

This paper presents a thorough numerical investigation focused on optimizing the efficiency of quantum-well intermediate-band solar cells (QW-IBSCs) based on III-nitride materials. The optimization strategy encompasses manipulating confinement potential energy, controlling hydrostatic pressure, adjusting compositions, and varying thickness. The built-in electric fields in (In, Ga)N alloys and heavy-hole levels are considered to enhance the results' accuracy. The finite element method (FEM) and Python 3.8 are employed to numerically solve the Schrödinger equation within the effective mass theory framework. This study reveals that meticulous design can achieve a theoretical photovoltaic efficiency of quantum-well intermediate-band solar cells (QW-IBSCs) that surpasses the Shockley-Queisser limit. Moreover, reducing the thickness of the layers enhances the light-absorbing capacity and, therefore, contributes to efficiency improvement. Additionally, the shape of the confinement potential significantly influences the device's performance. This work is critical for society, as it represents a significant advancement in sustainable energy solutions, holding the promise of enhancing both the efficiency and accessibility of solar power generation. Consequently, this research stands at the forefront of innovation, offering a tangible and impactful contribution toward a greener and more sustainable energy future.

Realizing a broad-scope and high-sensitivity optical thermometer based on dual-emission centers with structure confinement effect-related energy transfer

Based on dual-emission centers with a compact distance, a broad-scope optical thermometer with high sensitivity and temperature resolution is designed.

Encapsulation engineering of porous crystalline frameworks for delayed luminescence and circularly polarized luminescence.

Delayed luminescence (DF), including phosphorescence and thermally activated delayed fluorescence (TADF), and circularly polarized luminescence (CPL) exhibit common and broad application prospects in optoelectronic displays, biological imaging, and encryption. Thus, the combination of delayed luminescence and circularly polarized luminescence is attracting increasing attention. The encapsulation of guest emitters in various host matrices to form host-guest systems has been demonstrated to be an appealing strategy to further enhance and/or modulate their delayed luminescence and circularly polarized luminescence. Compared with conventional liquid crystals, polymers, and supramolecular matrices, porous crystalline frameworks (PCFs) including metal-organic frameworks (MOFs), covalent-organic frameworks (COFs), zeolites and hydrogen-bonded organic frameworks (HOFs) can not only overcome shortcomings such as flexibility and disorder but also achieve the ordered encapsulation of guests and long-term stability of chiral structures, providing new promising host platforms for the development of DF and CPL. In this review, we provide a comprehensive and critical summary of the recent progress in host-guest photochemistry via the encapsulation engineering of guest emitters in PCFs, particularly focusing on delayed luminescence and circularly polarized luminescence. Initially, the general principle of phosphorescence, TADF and CPL, the combination of DF and CPL, and energy transfer processes between host and guests are introduced. Subsequently, we comprehensively discuss the critical factors affecting the encapsulation engineering of guest emitters in PCFs, such as pore structures, the confinement effect, charge and energy transfer between the host and guest, conformational dynamics, and aggregation model of guest emitters. Thereafter, we summarize the effective methods for the preparation of host-guest systems, especially single-crystal-to-single-crystal (SC-SC) transformation and epitaxial growth, which are distinct from conventional methods based on amorphous materials. Then, the recent advancements in host-guest systems based on PCFs for delayed luminescence and circularly polarized luminescence are highlighted. Finally, we present our personal insights into the challenges and future opportunities in this promising field.

Scaling regimes for wormlike chains confined to cylindrical surfaces under tension.

We compute the free energy of confinement [Formula: see text] for a wormlike chain (WLC), with persistence length [Formula: see text], that is confined to the surface of a cylinder of radius R under an external tension f using a mean field variational approach. For long chains, we analytically determine the behavior of the chain in a variety of regimes, which are demarcated by the interplay of [Formula: see text], the Odijk deflection length ([Formula: see text]), and the Pincus length ([Formula: see text], with [Formula: see text] being the thermal energy). The theory accurately reproduces the Odijk scaling for strongly confined chains at [Formula: see text], with [Formula: see text]. For moderate values of f, the Odijk scaling is discernible only when [Formula: see text] for strongly confined chains. Confinement does not significantly alter the scaling of the mean extension for sufficiently high tension. The theory is used to estimate unwrapping forces for DNA from nucleosomes.

Temperature dependence of the electron and hole Landé g-factors in CsPbI3 nanocrystals embedded in a glass matrix.

The coherent spin dynamics of electrons and holes in CsPbI3 perovskite nanocrystals in a glass matrix are studied by the time-resolved Faraday ellipticity technique in magnetic fields up to 430 mT across a temperature range from 6 K to 120 K. The Landé g-factors and spin dephasing times are evaluated from the observed Larmor precession of electron and hole spins. The nanocrystal size in the three studied samples varies from about 8 to 16 nm, resulting in exciton transition varying from 1.69 to 1.78 eV at a temperature of 6 K, allowing us to study the corresponding energy dependence of the g-factors. The electron g-factor decreases with increasing confinement energy in the NCs as a result of NC size reduction, and also with increasing temperature. The hole g-factor shows the opposite trend. Model analysis shows that the variation of g-factors with NC size arises from the transition energy dependence of the g-factors, which becomes strongly renormalized by temperature.

STUDY OF THE VARIATIONS OF QUANTUM CONFINEMENT ENERGY WITH THE EXCITON BOHR RADIUS OF ZINC SELENIDE

In this work, the Brus model was used to study the variations of the Bohr diameter of the exciton with the quantum confinement energy. The results showed that the Bohr radius of the exciton decreases with an increase in the quantum confinement energy. This affects the properties of the material.

Impacts of Exciton Binding Energy and Dielectric Confinement of Layered Lead Halide Perovskites on Carrier Relaxation and Exciton Phonon Interactions.

This work highlights the significance of dielectric confinements and exciton binding energy of hybrid layered perovskites (LPs) in controlling the carrier relaxation dynamics of LPs for designing efficient optoelectronic devices. The polarizability of organic spacer cations in LPs modulates the carrier-phonon and carrier-carrier interactions, which eventually control the carrier relaxation dynamics. Here, we have varied the alkyl-ammonium chain length in the LPs to change the dielectric confinement, and the first-principles calculations reveal that the long-chain organic spacer experiences stronger dielectric confinement in comparison to short-chain organic spacer cation-based LPs. Transient absorption spectroscopic analysis suggests that the larger dielectric confinement and higher exciton binding energy exhibit faster carrier relaxation dynamics. The enhanced exciton-phonon interaction leads to faster carrier relaxation dynamics. The much softer phonon modes are responsible for the higher up-conversion of acoustic modes to optical modes, which leads to slower carrier relaxation dynamics in n-butylamine (BA) based LPs.

Overlooked role of void-nanoconfined effect in emerging pollutant degradation: Modulating the electronic structure of active sites to accelerate catalytic oxidation

The efficient removal of emerging pollutant from water is the ultimate frontiers of advanced oxidation processes (AOPs), yet it is challenging to obtain higher catalytic activity and oxidation rate. Herein, a sustainable solution was proposed by optimizing the curvature of confined structure to modulate the electronic state of the active sites in nanochannels for improving the catalytic activity. In addition, the confined effect can enhance the oxidation rate by shorting the mass transfer of active species and pollutants. A void-nanoconfined nanoreactor was prepared by loading Fe2O3 into the nanochannels (<5 nm) of the hollow carbon sphere. An enhancement of 3 orders of magnitude was obtained in the degradation rate constant of void-nanoconfined catalytic system toward sulfamethoxazole (SMX) (6.25 min−1) compared with the non-confined system. The kinetics enhancement was attributed to the larger electron potential difference between the outer and inner nanochannel caused by the curvature increase of carbon sphere, accelerating the electron transfer, so that the energy barrier of SMX degradation reaction was reduced by 31 kcal/mol with the assistance of confinement energy. Importantly, the NC-IN/PDS system exhibited outstanding removal efficiency for the actual river water using a continuous flow reactor. This work provides a new insight into designing an efficient and stable catalytic nanoreactor, enriching the domain of advanced wastewater treatment strategies.

Nonlinear optical properties of coupled quantum dots in peanut configuration

ABSTRACT This paper presents a theoretical investigation of nonlinear properties of coupled quantum dots in the peanut configuration. A complete Hamiltonian is formulated using the adiabatic method and the confinement energy is represented in a cylindrical coordinate system. The effective energy for the slow subsystem is analysed and graphed as a function of a fixed value of axial coordinate for both the asymmetric and symmetric peanut QD cases. The electron motion in the presence of an electric field in the vertical direction is considered, and the eigenfunctions and energy spectrum of electron motion are determined for the same direction utilising the finite element method. The dependence of the first three energy levels on the electric field is shown, and the electron probability density for the ground state and the first excited state is plotted. In addition, calculations for the nonlinear optical properties are presented, particularly optical rectification, second harmonic generation and third harmonic generation. The results demonstrate that these properties can be effectively controlled by varying the external electric field. The findings suggest that coupled peanut QDs hold significant potential for applications in high-performance optoelectronic devices.

Cation Exchange and Spontaneous Crystal Repair Resulting in Ultrathin, Planar CdS Nanosheets.

Cation exchange has become a major postsynthetic tool to obtain nanocrystals with a combination of stoichiometry, size, and shape that is challenging to achieve by direct wet-chemical synthesis. Here, we report on the transformation of highly anisotropic, ultrathin, and planar PbS nanosheets into CdS nanosheets of the same dimensions. We monitor the evolution of the Cd-for-Pb exchange by ex-situ TEM, HAADF-STEM, and EDX. We observe that in the early stages of the exchange the sheets show large in-sheet voids that repair spontaneously upon further exchange and annealing, resulting in ultrathin, planar, and crystalline CdS nanosheets. After cation exchange, the nanosheets show broad sub-band gap luminescence, as often observed in CdS nanocrystals. The photoluminescence excitation spectrum reveals the heavy- and light-hole exciton features, with very strong quantum confinement and large electron-hole Coulomb energy, typical for 2D ultrathin Cd-chalcogenide nanosheets.