Light Hole Research Articles

Mitigation of di-(2-ethylhexyl) phthalate contamination exposure over supramolecular organic heterojunction

Di-(2-ethylhexyl) phthalate (DEHP) with endocrine disrupting toxicity has been widely concerned owing to its widespread presence in environment and food. As an essential part of the daily diet, edible oil has become an emerging and nonnegligible source of DEHP intake exposure. Herein, we demonstrated a two-step method to mitigate DEHP exposure from edible oil including firstly selective adsorption and then photocatalytic degradation by supramolecular organic nanomaterial composites. Perylene diimide (PDI) heterojunction with Bi2WO6 was synthesized by a facile ultrasonic-water bath heating method. It was found that PDI/Bi2WO6 showed selective adsorption of DEHP in edible oil via π-π stacking, hydrophobic interactions, and monolayer chemisorption compared with other phthalates. Adsorption kinetics and isotherm simulation results showed that the adsorption process conformed to the second-order kinetics and Langmuir model. Then, under visible light irradiation, PDI/Bi2WO6 with 35 % m(PDI)/m(Bi2WO6) had the highest degradation rate of DEHP, which was 2.16 and 1.76 times higher than that of PDI and Bi2WO6, respectively. The reactive species generated under visible light irradiation, superoxide radicals (•O2−), hydroxyl radicals (•OH), and holes (h+) were synergistically involved in the photodegradation of DEHP to the intermediates of mono(2-ethylhexyl) phthalate (MEHP), mono-dibutyl phthalate (MBP), phthalic acid (PA), and 4-oxohexanoic acid. These findings may provide a technology for minimizing and treating contaminants exposure in the environment and foodstuffs through supramolecular organic nanomaterial heterojunction.

Calculation of Curie Temperature and Carriers Effective Masses of (Ga, Mn)As Diluted Magnetic Semiconductor from the Eight-Band k.p Model

An important step toward the development of spintronic information processing, transfer, and storage devices is the discovery of a dilute magnetic semiconductor (DMS) that demonstrates carrier-mediated ferromagnetism and maintains its magnetic properties above room temperature. Despite considerable progress made in recent decades, the maximum Curie temperature (∼200 K) remains well below room temperature. Mndoped GaAs are among the various diluted magnetic semiconductor materials that have been studied and have emerged as one of the most promising contenders for technological usage. The key characteristic of GaMnAs is its ferromagnetic properties, which are critical for spintronic devices. The primary goal of this work is to compute two critical properties of GaMnAs: the effective masses and the Curie temperature. The 8-band k.p model put forth by Kane was utilized to compile the GaMnAs band parameters using a MATLAB program. Our calculations are based on Lowdin perturbation theory, where spin-orbit, sp-d exchange interaction, and biaxial strain are taken into account. We calculated the Curie temperature of the GaMnAs alloy, within the mean-field approach based on the Zener model. Our findings demonstrated a direct proportionality relationship between the Curie temperature and the hole concentration (p) in GaMnAs. Moreover, we looked into how the Mn content and strain affected the effective masses of electrons, heavy, and light holes that were calculated for various crystallographic directions in GaMnAs. The effective masses that were calculated were highly dependent on the Mn content, which ranged from 1% to 5%, and the strain, which varied from −2% (tensile strain) to 2% (compressive strain).

Constraining burdened PBHs with gravitational waves

We investigate the implications of memory burden on the gravitational wave (GW) spectrum arising from the Hawking evaporation of light primordial black holes (PBHs). By considering both rotating (Kerr) and non-rotating (Schwarzschild) PBHs, we demonstrate that the overproduction of primordial GWs from burdened PBHs could impose stringent constraints on the parameters governing backreaction effects. These constraints, derived from ΔN eff measurements by Planck and prospective experiments such as CMB-S4 and CMB-HD, offer novel insights into the impact of memory burden on PBH dynamics.

Memory burden effect in black holes and solitons: Implications for PBH

The essence of the memory burden effect is that a load of information carried by a system stabilizes it. This universal effect is especially prominent in systems with a high capacity of information storage, such as black holes and other objects with maximal microstate degeneracy, the entities universally referred to as “saturons.” The phenomenon has several implications. The memory burden effect suppresses a further decay of a black hole, the latest, after it has emitted about half of its initial mass. As a consequence, the light primordial black holes that previously were assumed to be fully evaporated are expected to be present as viable dark matter candidates. In the present paper, we deepen the understanding of the memory burden effect. We first identify various memory burden regimes in generic Hamiltonian systems and then establish a precise correspondence in solitons and in black holes. We make transparent, at a microscopic level, the fundamental differences between the stabilization by a quantum memory burden versus the stabilization by a long-range classical hair due to a spin or an electric charge. We identify certain new features of potential observational interest, such as the model-independent spread of the stabilized masses of initially degenerate primordial black holes. Published by the American Physical Society 2024

Impact of the Interruption Duration on Photoluminescence Properties of MOCVD-Grown GaAsP/InAlGaAs Quantum Well Structures.

The growth interruption technology is introduced to the growth of GaAsP/InAlGaAs quantum well (QW) structure using metal-organic chemical vapor deposition (MOCVD). The effect of growth interruption time (GIT) on the crystalline quality and optical properties are investigated. The two distinctive emission peaks are the transition recombination between the electron level of conduction band and the light and heavy hole level of valence band in the photoluminescence (PL) at room temperature. The PL peaks present a redshift and merge together with the increasing GIT, which is attributed to the QW energy level shift caused by the increase in arsenic concentrations in GaAsP QW, the diversified thickness of QW and the variations of indium components in the InAlGaAs barrier layer. The Gaussian deconvolution parameters in temperature-dependent PL (TDPL) show that the GaAsP/InAlGaAs QW with a GIT of 6 s has a 565.74 meV activation energy, enhancing the carrier confinement in QW and the PL intensity, while the 6 s-GIT GaAsP QW has the increasing interface roughness and the non-radiative centers at the InGaAsP intermediate layer, leading to a spectral broadening. The QW with 10 s-GIT exhibits a small full width at half maximum (FWHM) with the various temperature, indicating reduced interface roughness and excellent crystal quality. An increase in GIT may be suitable for optimizing the optical properties of GaAsP/InAlGaAs QW.

Influence of Mixing Valence Band States to the Conduction Band States on Two-Quantum Linear-Circular Dicroism in Semiconductors

A quantitative theory of two-photon linear-circular dichroism caused between the subbands of light and heavy holes of the valence band and conduction band is constructed, which takes into account the admixture of valence band states to the conduction band states and the temperature dependence of the band gap (Eg(T)) in semiconductors of tetrahedral symmetry in the multiband Kane model. It is shown that the type of oscillatory angular dependence or the amplitude values of the probabilities of two-photon optical transitions depend on the state of light polarization. This is due to the fact that, under the influence of linearly polarized light, alignment along the pulse occurs, and under the action of circularly polarized light, the moments of current carriers are oriented. It has been determined that the probability of two-photon optical transitions from the heavy hole subband to the conduction band of semiconductors at a fixed temperature increases with increasing frequency, passes through a maximum, and sharply decreases regardless of the degree of polarization of light, as well as the band gap.

Optical Characterization of the Interband Cascade LWIR Detectors with Type-II InAs/InAsSb Superlattice Absorber.

The long-wave infrared (LWIR) interband cascade detector with type-II superlattices (T2SLs) and a gallium-free ("Ga-free") InAs/InAsSb (x = 0.39) absorber was characterized by photoluminescence (PL) and spectral response (SR) methods. Heterostructures were grown by molecular beam epitaxy (MBE) on a GaAs substrate (001) orientation. The crystallographic quality was confirmed by high-resolution X-Ray diffraction (HRXRD). Two independent methods, combined with theoretical calculations, were able to determine the transitions between the superlattice minibands. Moreover, transitions from the trap states were determined. Studies of the PL intensity as a function of the excitation laser power allowed the identification of optical transitions. The determined effective energy gap (Eg) of the tested absorber layer was 116 meV at 300 K. The transition from the first light hole miniband to the first electron miniband was red-shifted by 76 meV. The detected defects' energy states were constant versus temperature. Their values were 85 meV and 112 meV, respectively. Moreover, two additional transitions from acceptor levels in cryogenic temperature were determined by being shifted from blue to Eg by 6 meV and 16 meV, respectively.

(Invited) III-Nitride Ultraviolet LEDs and Lasers for Applications in Biology and Medicine

Ultraviolet (UV) light emitters with large-energy photons are being developed for emerging biology and medicine applications such as sterilization, water/air purification, and medical treatments, as a replacement for mercury vapor lamps. Solid-state UV light-emitting diodes (LEDs) and lasers based on wide bandgap III-Nitrides offer compact sizes, wavelength tuning, long lifetimes, and sustainability over mercury vapor lamps. While visible LEDs and lasers with longer emission wavelengths find widespread commercial uses for solid-state lighting and display, UV emitters with AlGaN heterostructures struggle with poor external quantum efficiencies of typically less than 10%, which drop further when wavelengths get shorter. Therefore, it is extremely challenging to realize high-efficiency UV emitters despite the demand for compact UV light source, especially for disinfection and sterilization from the pandemic as those high-energy photons can break DNA/RNA bonds and deactivate virus/bacteria. Here, I will discuss our recent developments toward realization of high-efficiency UV LEDs and lasers.To enhance the radiative recombination rate (R sp) from the AlGaN quantum well (QW) active region, we had pursued novel QW design to overcome issues from the existence of valence subbands crossover. Specifically, the arrangement of the three energy-degenerate valence subbands - heavy hole (HH), light hole (LH), and the crystal-field split-off hole (CH) bands for high Al-content and low Al-content AlGaN QWs are completely different. The ordering of the valence bands strongly affects the optical matrix element via the oscillator strength, as well as the direction of the photon emission. Our work has proposed promising solution on the use of delta-QW design to address the valence subbands crossover issue, in order to significantly boost up the R sp. In addition, to enhance the extraction efficiency of UV emitters, we demonstrated the realization and characterization of top-down fabricated, electrically driven UV micropillar array LEDs emitting at 286 nm with a narrow, 9 nm linewidth and output power densities up to 35 mW/cm2. Top-down fabrication allows for formation of perfectly uniform arrays of micropillars with easily tunable diameter and pitch, which cannot be achieved with epitaxially grown nanowires without the use of selective area epitaxy. Dry etch damage induced surface losses were avoided through the use of a two-step etch process combining a Cl dry etch and a hydroxyl-based wet etch to form the micropillar arrays. We also revealed that the unique inverse-taper profile of our micropillars could produce significant enhancements in the extraction efficiency with the increased taper angle. Lastly, our developed III-Nitride wet etch by the use of hydroxyl-based chemicals such as potassium hydroxide (KOH) investigated the effects of temperature, concentration, and the damage recovery aspects of hydroxyl etching of III-Nitride nano and micro structures, leading to important smooth surface profiles for micropillar/nanowire LEDs and optimized mirror facets for ridge-emitting UV lasers.

Determining the spin of light primordial black holes with Hawking radiation. Part II. High spin regime

We propose a method to determine the mass and spin of primordial black holes based on measuring the energy and emission rate at the dipolar and quadrupolar peaks in the primary photon Hawking spectrum, applicable for dimensionless spin parameters a~\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\overset{\\sim }{a} $$\\end{document} ≳ 0.6. In particular, we show that the ratio between the energies of the two peaks is only a function of the black hole spin, while the ratio between their emission rates depends also on the line-of-sight inclination. The black hole mass and distance from the Earth may then be inferred from the absolute values of the peak energies and emission rates. This method is relevant for primordial black holes born with large spin parameters that are presently still in the early stages of their evaporation process. While Hawking radiation from such black holes is somewhat below the reach of planned gamma-ray telescopes, we expect the required sensitivity to be attained in the not too distant future.

Strong high-energy exciton electroluminescence from the light holes of polytypic quantum dots

High-energy exciton emission could allow single-component multi-colour display or white light-emitting diodes. However, the thermal relaxation of high-energy excitons is much faster than the photon emission of them, making them non-emissive. Here, we report quantum dots with light hole-heavy hole splitting exhibiting strong high-energy exciton electroluminescence from high-lying light holes, opening a gate for high-performance multi-colour light sources. The high-energy electroluminescence can reach 44.5% of the band-edge heavy-hole exciton emission at an electron flux density Φe of 0.71 × 1019 s−1 cm−2 − 600 times lower than the photon flux density Φp (4.3 × 1021 s−1 cm−2) required for the similar ratio. Our simulation and experimental results suggest that the oscillator strength of heavy holes reduces more than that of light holes under electric fields. We attribute this as the main reason for strong light-hole electroluminescence. We observe this phenomenon in both CdxZn1-xSe-ZnS and CdSe-CdS core-shell quantum dots exhibiting large light hole-heavy hole splittings.

Possible Wigner states in CrI3 heterostructures with graphene: A tight-binding model perspective

In this study, we present an effective tight-binding model for an accurate description of the lowest energy quadruplet of a conduction band in a ferromagnetic CrX3 monolayer, tuned to the complementary density functional theory simulations. This model, based on a minimum number of chromium orbitals, captures a distinctively flat dispersion in those bands but requires taking into account hoppings beyond nearest neighbors, revealing ligand-mediated electron pathways connecting remote chromium sites. Doping of states in the lowest conduction band of CrX3 requires charge transfer, which, according to recent studies [Tenasini , ; Tseng , ; Cardoso , , can occur in graphene(G)/CrX3 heterostructures. Here, we use the detailed description of the lowest conduction band in CrI3 to show that G/CrI3/G and G/CrI3 are type-II heterostructures where light holes in graphene would coexist with heavy electrons in the magnetic layer, where the latter can be characterized by Wigner-Seitz radius rs∼25−35 (as estimated for hBN-encapsulated structures). Published by the American Physical Society 2024

Revisiting string-inspired running-vacuum models under the lens of light primordial black holes

Revisiting string-inspired running-vacuum models under the lens of light primordial black holes

Evaporation of Primordial Charged Black Holes: Timescale and Evolution of Thermodynamic Parameters

The evolution of primordial black holes formed during the reheating phase is revisited. For reheating temperatures in the range of 1012–1013 GeV, the initial masses are respectively of the order of 1010–108MP, where MP is the Planck mass. These newborn black holes have a small charge-to-mass ratio of the order of 10−3, a consequence of statistical fluctuations present in the plasma constituting the collapsing matter. Charged black holes can be rapidly discharged by the Schwinger mechanism, but one expects that, for very light black holes satisfying the condition M/MP<<MP/mW (mW is the mass of the heaviest standard model charged W-boson), the pair production process is probably strongly quenched. Under these conditions, these black holes evaporate until attaining extremality with final masses of about 107–105MP. Timescales to reach extremality as a function of the initial charge excess were computed, as well as the evolution of the horizon temperature and the charge-to-mass ratio. The behavior of the horizon temperature can be understood in terms of the well-known discontinuity present in the heat capacity for a critical charge-to-mass ratio Q/GM=3/2.

Poly(ionic liquid) composite oxygenated graphite carbon nitride for enhanced photocatalytic and synergistic bacteriostasis

AbstractWith the increase of drug‐resistant bacteria and the limitations of traditional antibacterial methods, photocatalytic inhibition has received widespread attention as a novel antibacterial method. In this paper, poly(1‐vinyl‐3‐ethylimidazolium tetrafluoroborate) composite oxygenated carbon nitride (PBF‐OCN) were prepared by in situ free radical polymerization using 1‐vinyl‐3‐ethylimidazolium tetrafluoroborate and OCN. The results showed that the light absorption ability and electron hole separation rate of PBF‐OCN were greatly improved compared with that of OCN, and the rate constant for photocatalytic removal MB of PBF‐OCN‐1 was about 1.39 times of that OCN. The growth of Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) could be significantly inhibited by PBF‐OCN under visible light, among which, the inhibition of PBF‐OCN‐3 was the most excellent, with the diameter of the circle of inhibition reaching 20.69 mm for E. coli, and 21.30 mm for S. aureus, and the inhibition rate against E. coli calculated by plate counting method reached 97.0%. The minimum inhibitory concentration for E. coli and S. aureus was 0.0625 mg/mL, respectively, and the possible inhibition mechanism of the samples was explored. The good synergistic antibacterial effect of PBF‐OCN is expected to be applied in water treatment, antibacterial devices, packaging materials, and other fields.

Ambipolar Charge Injection and Bright Light Emission in Hybrid Oxide/Polymer Transistors Doped with Poly(9‐Vinylcarbazole) Based Polyelectrolytes

AbstractLight‐emitting transistors (LETs) are a remarkable, emerging class of electronic devices that combine the switching function of field‐effect transistors (FETs) and the light‐emitting function of light‐emitting diodes (LEDs). In order to achieve efficient light emission, effective electron and hole injection from source and drain electrodes is necessary. Various strategies have been introduced to accomplish this, such as incorporating asymmetric electrodes or charge injection layers during device fabrication. These approaches have inevitably introduced complexity in the device fabrication process. Herein, light‐emitting electrochemical transistors (LECTs) are demonstrated that combine principles of electrochemistry and optoelectronics to achieve multi‐functionality in a simple device architecture. Hybrid polyelectrolytes, poly(9‐vinylcarbazolesulfonate)‐ lithium and copper (II) salts (PVK‐Li and PVK‐Cu) incorporating Li+ ion and Cu2+ ions are added at variable concentrations to the organic emitting layer of LECTs to effect electrochemical p‐type doping. This electrochemical doping approach yielded improvements in electrical and optical performances including mobilities, brightnesses, and external quantum efficiency of the LECTs. The dynamics of how charges including ions, electrons, and holes move and interact are discussed in the device to facilitate emissive charge carrier recombination and light emission. This investigation provides valuable insights into the realms of both electrochemistry and optoelectronics.

Breakdown of hawking evaporation opens new mass window for primordial black holes as dark matter candidate

ABSTRACT The energy injection through Hawking evaporation has been used to put strong constraints on primordial black holes as a dark matter candidate at masses below 1017 g. However, Hawking’s semiclassical approximation breaks down at latest after half-decay. Beyond this point, the evaporation could be significantly suppressed, as was shown in recent work. In this study we review existing cosmological and astrophysical bounds on primordial black holes, taking this effect into account. We show that the constraints disappear completely for a reasonable range of parameters, which opens a new window below 1010 g for light primordial black holes as a dark matter candidate.

Searching for Exploding black holes

The observation of the final stages of the evaporation of a light black hole, which Hawking referred to as “black hole explosion”, would offer critical insights on quantum gravity and high-energy physics phenomena. Here, we explore, review, and revisit the observational features and rates expected for nearby, light, evaporating black holes, and we assess and compare the expected sensitivity of a broad range of observatories. We then focus on the search for candidate black hole explosions in archival data from the Fermi Large Area Telescope and Gamma-ray Burst Monitor, and outline possible future observational campaigns.

Теплопровідність твердих розчинів GeBiTe

The paper calculates the electronic and lattice components of thermal conductivity coefficients for GeBiTe solid solutions. The calculation was carried out using two different models of the band structure of GeTe, which differ in the relative location of the zones of heavy and light holes. The first of the models is generally accepted for A4B6 compounds and assumes the location of the zone of light holes above the zone of heavy ones in the energy spectrum. Another model, obtained on the basis of DFT calculation, predicts the location of the zone of light holes below the zone of heavy ones. A significant difference was established in the numerical values of the electronic and lattice components of the thermal conductivity coefficients, depending on the adopted model. The influence of other calculation parameters on the investigated values was analyzed.

Investigating black hole accretion disks as potential polluter sources for the formation of enriched stars in globular clusters

Accretion disks surrounding stellar mass black holes have been suggested as potential locations for the nucleosynthesis of light elements, which are our primary observational discriminant of multiple stellar populations within globular clusters. The population of enriched stars in globular clusters are enhanced in N Na and sometimes in Al and/or in K . In this study, our aim is to investigate the feasibility of initiating nucleosynthesis for these four elements in black hole accretion disks, considering various internal parameters such as the temperature of the gas and timescale of the accretion. To achieve this, we employed a 132-species reaction network. We used the slim disk model, suitable for the Super-Eddington mass accretion rate and for geometrically and optically thick disks. We explored the conditions related to the mass, mass accretion rate, viscosity, and radius of the black hole-accretion disk system that would allow for the creation of N Na Al and K before the gas is accreted onto the central object. This happens when the nucleosynthesis timescale is shorter than the viscous timescale. Our findings reveal that there is no region in the parameter space where the formation of Na can occur and only a very limited region where the formation of N Al and K is plausible. Specifically, this occurs for black holes with masses lower than 10 solar masses ($m<10 M_ with a preference toward even lower mass values ($m<1 M_ and extremely low viscosity parameters ($ $). Such values are highly unlikely based on current observations of stellar mass black holes. However, such low mass black holes could actually exist in the early universe, as so-called primordial black holes. In conclusion, our study suggests that the nucleosynthesis within black hole accretion disks of elements of interest for the multiple stellar populations, namely N Na Al and K is improbable, but not impossible, using the slim disk model. Future gravitational wave missions will help constrain the existence of tiny and light black holes.

Dimensional quantization in InSb and GaAs in three-zone model

Various cases of size quantization in narrow-gap crystals of cubic or tetrahedral symmetry in the three-band Kane approximation are analyzed. Expressions for the energy spectrum depending on the two-dimensional wave vector are obtained for two different cases, differing in the range of current carrier energy values. The size-quantized energy spectrum of electrons in the conduction band and holes in the subband of light holes in InSb and GaAs semiconductors is analyzed in the three-band Kane model.