Hydrogenic Impurity Research Articles

Optical absorption coefficient of a hydrogenic impurity in a surface quantum well

In this study, the first excited state binding energy and the linear, non-linear and total optical absorption coefficients (OAC) of a hydrogenic impurity in a surface quantum well (SQW) of the type vacuum/GaAs/AlxGa1-xAs are calculated as functions of the incident photon energy, the Al content and the well width using a variational method within the effective mass approximation. The results show that the first excited state energy and the linear, non-linear and total OAC are strongly influenced by variations in the well width, and only a slight, yet interesting, impact of the Al content is observed. A redshift in the extreme values of the linear, non-linear and total OAC is found for a SQW with fixed Al content and variable width, whereas no significant variation is observed in the reciprocal system of fixed width and variable Al content.

Degradation prediction of proton exchange membrane fuel cell using a novel neuron-fuzzy model based on light spectrum optimizer

Proton exchange membrane fuel cell (PEMFC) is regarded as the most promising clean energy to address the fossil energy crisis and environmental pollution. However, it is susceptible to frequently variable load and the impurities of hydrogen, which can directly cause the degradation of performance over time during operations. Degradation prediction has received much attention in recent years, as it can improve the durability and reliability of the PEMFC system. This paper proposes an effective multi-step-ahead prediction for PEMFC degradation under various operational conditions by using variational mode decomposition (VMD), a double recurrent fuzzy neural network (DRFNN), and a light spectrum optimizer (LSO). The integrated method enables precise prediction of degradation trends of PEMFC using historical testing data, which brings together their advantages. To better learn degradation trends, VMD is applied to decompose the input voltage signal into a series of sub-signals with a simpler structure. Then, DRFNN with a feedback loop is developed to train each sub-signal model, which can learn and memorize past information. To further enhance the prediction precision of degradation model, LSO is adopted to automatically update the network’s weights. Finally, the prediction performance of the proposed method is experimentally verified under different load conditions. Compared with other degradation methods, the test results reveal that the proposed method can achieve significant improvements in terms of multi-step-ahead prediction accuracy and robustness.

Theoretical investigation of optoelectronic properties in PbS/CdS core/shell spherical quantum dots under the effect of the electric field intensity, hydrogenic impurity and geometric parameters

In this paper, we theoretically investigated the combined effects of the external electric field (EF) strength and the geometric parameters on the linear, nonlinear and total dielectric functions as well as the effective dielectric function (DF) coefficients of PbS/CdS spherical core/shell quantum dots (CSQD) in the presence of the hydrogenic impurity located at the center. The subband energy eigenvalues and their corresponding wave functions are obtained by solving the time-independent Schrödinger equation and using the variational method (VM) in the framework of the effective mass approximation (EMA). The linear, nonlinear and total DF as well as the effective DF were discussed and evaluated under the influence of EF intensity, geometric parameters, the change of the number of quantum dots (QDs) per unit volume and optical intensity I based on the compact density matrix (CDM) approach. The obtained results show that the height peaks of the linear, nonlinear and Total DF as well as the effective DF coefficients increase and their resonant peak moves towards lower energies as the EF and geometric factors increase in both cases with and without considering the hydrogenic impurity effect. Furthermore, our findings show that the impact of optical intensity and the number of QDs per unit volume does not change the resonance peaks of imaginary parts of DF and effective DF but decreases their magnitudes. As a result, we believe that numerical results will present important developments and provide great contributions in designing new optoelectronic devices related to CSQD hetero-nanostructure.

The combined effects of electric field and embedded dielectric matrix on the electronic and optical properties in Ge/SiGe core/shell quantum dots and its SiGe/Ge inverted structure

In this study, the binding energy (BE) and photoionization cross-section (PICS) coefficients in a Ge/Si0.15Ge 0.85 core/shell quantum dots (CSQDs) and in its inverted structure Si0.15Ge0.85 / Ge (ICSQDs) are studied. The influence of the hydrogenic impurity and capped matrix are taken into account. The electronic states and their related eigenfunctions are computed by solving the three-dimensional Schrödinger equation under the framework of the effective mass approximation (E.M.A) using the variational dimensional. The influence of the core radius and electric field strength on the BE and PICS are investigated. The numerical results reveal that the optoelectronic properties are considerably affected by the electric field strength (EF), immersed oxide matrix (OM) and geometric parameter. The obtained results prove that the PICS magnitude increases as the core radius increases and its resonant peak moves towards the lower energies for Ge/Si0.15Ge0.85 CSQDs structure, and increases as the core radius decreases and its resonant peak experiences a blue shift with increasing core radius for Si0.15Ge 0.85/ Ge ICSQDs. Moreover, with the effects of the surrounding oxide matrix and electric field strength, the PICS magnitude is improved and their resonant peak suffers a redshift.

Demonstration of aneutronic p-11B reaction in a magnetic confinement device

Aneutronic fusion using commonly available fuel such as hydrogen and boron 11 (11B) is one of the most attractive potential energy sources. On the other hand, it requires 30 times higher temperature than deuterium–tritium fusion in a thermonuclear fusion reactor condition. Development of techniques to realize its potential for the experimental capability to produce proton-boron 11 (p-11B) fusion in the magnetically confined fusion device using neutral beam injection is desired. Here we report clear experimental exploration and measurements of p-11B fusion reactions supported by intense hydrogen beams and impurity powder dropper installed in the magnetic confinement plasma Large Helical Device. We measured a significant amount of fusion alpha particle emission using a custom designed alpha particle detector based on a passivated implanted planar silicon detector. Intense negative-ion-based hydrogen beam injectors created a large population of up to 160 keV energetic protons to react with the boron-injected plasma. The p-11B alpha particles having MeV energy were measured with the alpha particle detector which gave a fusion rate in a good agreement with the global p-11B alpha emission rate calculated based on classical confinement of energetic proton, using experimentally obtained plasma parameters.

Ethylenediamine tetramethylenephosphonic acid boosting the electrocatalytic interface construct and proton transfer for high-temperature polymer electrolyte membrane fuel cells

High-temperature polymer electrolyte membrane fuel cells (HT-PEMFCs) show excellent application prospects due to its enhanced tolerance of hydrogen impurity. However, the sluggish electrode kinetics caused by its inefficient electrocatalytic interface and proton transfer severely restricts its performance. To overcome the sluggish electrode kinetics, the ethylenediamine tetramethylenephosphonic acid (EDTMPA) was successfully incorporated into the catalysts layer to regulate the phosphoric acid (PA) distribution to boost the electrocatalytic reaction interface and proton transfer, thus increasing the output power and stability of HT-PEMFCs. The hydrophilic H2PO4− and electron donor N atom of EDTMPA could efficiently decrease the absorption of PA on the catalyst surface and facilitate proton transportation in the membrane electrode, as demonstrated by our experiments. The fuel cell assembled with the prepared membrane electrode shows a high reactivity of 1175 mW cm−2 and excellent stability, which is much better than the past reference report. The results of this work provide new insights into the utilization of small molecules with phosphate groups to enhance phosphate tolerance and proton conduction, and there is also a further improvement in the reactivity, durability, and utilization of the electrocatalysts in HT-PEMFCs.

Electric field-induced modulation of electronic and optical properties in doped CdTe/CdS core/shell quantum dots embedded in an oxide matrix

This work presents a theoretical analysis of a CdTe/CdS core/shell quantum dots embedded in a dielectric oxide matrix under the influence of hydrogenic impurity and the applied electric field intensity. The eigenstates and their corresponding eigenfunctions are computed by solving the Schrodinger equation using the finite element method within the effective mass approximation. The first-order linear and third-order nonlinear optical absorption coefficients as well as the refractive index changes are computed based on the compact density matrix approach. The obtained result shows that the first-order linear and third-order nonlinear optical properties are more pronounced with the electric field, surrounding oxide matrix and the donor impurity effects. However, the first-order linear and third-order nonlinear optical absorption coefficients and refractive index changes can experience a red or blue shift under the influence of electric field, oxide matrix and hydrogenic impurity. In addition, under all conditions, the height peaks of these optical properties can be raised (fall). Our findings demonstrate the critical importance of considering the roles of electric field, the presence of donor impurity, and the capped dielectric oxide matrix in the design and fabrication of core–shell-based optoelectronic devices.

Binding Energies and Optical Properties of Power-Exponential and Modified Gaussian Quantum Dots.

We examine the optical and electronic properties of a GaAs spherical quantum dot with a hydrogenic impurity in its center. We study two different confining potentials: (1) a modified Gaussian potential and (2) a power-exponential potential. Using the finite difference method, we solve the radial Schrodinger equation for the 1s and 1p energy levels and their probability densities and subsequently compute the optical absorption coefficient (OAC) for each confining potential using Fermi's golden rule. We discuss the role of different physical quantities influencing the behavior of the OAC, such as the structural parameters of each potential, the dipole matrix elements, and their energy separation. Our results show that modification of the structural physical parameters of each potential can enable new optoelectronic devices that can leverage inter-sub-band optical transitions.

New developments of hydrogen impurity online-monitoring in liquid lithium of IFMIF-DONES

On the way to future nuclear fusion power plants, the International Fusion Materials Irradiation Facility (IFMIF) – DEMO Oriented Neutron Source (DONES), is an important key element between ITER and DEMO to study before the influence of DEMO-neutron irradiation on foreseen fusion materials. The core of DONES, currently under construction near Granada, Spain, is based on a circuit containing liquid lithium at elevated temperatures acting as a functional material for the (d,n)-Li reaction in a materials test cell. In addition to this actual function of DONES, there are important aspects of maintenance in which hydrogen isotopes are generated under operating conditions and dissolved in this aggressive and very reactive alkali metal. This implies strong unfavourable effects on the applied structural materials, e.g. hydrogen embrittlement and others.To counteract these unfavourable effects, endangering the safe operation, an Impurity Control System (ICS) is an integral part of the DONES instrumentation. As part of the tasks of the European Neutron Source (ENS) to develop redundant systems for monitoring impurities, a special sub-task was defined for the development of an electrochemical H-sensor for concentrations in liquid lithium, ECHSLL. It is determined by detecting the electrical potentials of the lithium melts compared to a standard Li-based chemical reference system. This allows an inherent material property to be directly correlated (i.e. through appropriate electrochemical instrumentation) with chemical concentration values. This article presents important advancements in the applied ECHSLL technique, such as improving laboratory measurements from stagnant conditions to dynamic and realistic flow conditions of the liquid lithium material, as well as appropriate approaches to overcome the challenges in distinguishing the hydrogen isotopes by ECHSLL system (protium and deuterium among given laboratory conditions).

First-principles study of defects and doping limits in CaO

Calcium oxide (CaO) is a promising host for quantum defects because of its ultrawide bandgap and potential for long spin coherence times. Using hybrid functional calculations, we investigate the intrinsic point defects and how they limit Fermi-level positions and doping in CaO. We find calcium and oxygen vacancies to be the most common intrinsic defects, acting as compensating acceptors and donors, respectively. Oxygen interstitials are also prevailing under O-rich conditions and act as compensating donors. Due to compensation by these defects, O-poor conditions are required to dope CaO n-type, while O-rich conditions are required for p-type doping. We find that, at room temperature, intrinsic CaO can only achieve Fermi-level positions between 1.76 eV above the valence-band maximum (VBM) and 1.73 eV below the conduction-band minimum (CBM). If suitable shallow dopants are found, the allowed range of Fermi levels would increase to between VBM + 0.53 eV and CBM − 0.27 eV and is set by the compensating intrinsic defects. Additionally, we study hydrogen impurities, and show that hydrogen will not only limit p-type doping but can also act as shallow donor when substituting oxygen (HO defects).

The Q-cascade Theory with Material Losses and Gains

Material losses and gains are generally unavoidable in isotope separation cascades because of air leakage into the cascade and chemical reactions of the materials in contact with the process gas. Both losses and gains are incorporated into the well-known Q-cascade theory and can be considered differently for each component. The theory is applied, as an example, to investigating the separation of natural uranium to produce low-enriched uranium of 5% 235U, in which UF6 incurs material losses, generating the light impurity hydrogen fluoride (HF). Two approaches are discussed, one using a carrier gas and another purging the light impurity to prevent the light impurity from exceeding the upper limit in the cascade product end for safe cascade operation. The results show that using carrier gas increases the relative total flow of the cascade, whereas purging the light impurity requires the development of a purging technology. The investigation presents a complicated but real practical scenario, where the components of different physical and chemical properties (some with and without material losses, and some with gains) all appear in the process gas, and demonstrates the applicability of the theory in the study of separation cascades.

Optical measurements of solid nitrogen solubility in hydrogen at cryogenic temperatures

The solubility of impurities in hydrogen at cryogenic temperatures is essential information for the design of liquid hydrogen plants. However, large data scatter and inconsistent predictions of impurity solubility by thermodynamic models mean that expensive engineering design margins are required to avoid blockages in cryogenic equipment. Here we report the combination of a stereomicroscope, commercial cryocooler and pressure cell to directly visualise solid impurity freeze-out and melting in stirred hydrogen at low temperatures and elevated pressures. Scattered literature data for nitrogen's solubility in hydrogen are compared to new solid-fluid equilibrium (SFE) measurements for a 1000 ppm N2 in H2 mixture at (1.8–5) MPa, and (42–52) K. These results were used to improve solubility models implemented in the ThermoFAST software package, achieving a three-fold decrease in the root-mean-square deviations between the SFE predictions and the data, helping lower the risk of impurity freeze-out in hydrogen liquefaction.

Hydrogen in natural diamond: Quantification of N3VH defects using SIMS and FTIR data

A set of ten diamonds from different sources representing the main types of physical classification (IaA, IaAB, IaB and IIa) has been first explored by FTIR spectroscopy and SIMS calibrated by hydrogen ion implantation. The concentrations of hydrogen in the studied diamonds measured by SIMS range between 9.98 and 47.6 at.ppm or from 1.76 × 1018 to 8.40 × 1018 at./cm3. The 3107 cm−1 absorption line has been detected by FTIR spectroscopy (resolution near 1 cm−1) in five studied diamonds (IaB and IaAB). The 3107 cm−1 IR absorption lines due to H defects in these diamonds have been successfully described by the Lorentzian shape and their parameters have been evaluated. Based on the linear regression equation relating intensities of the 3107 cm−1 IR absorption lines in the studied diamonds with their H defect concentrations, the H defect IR absorption at 3107 cm−1 in diamond has been quantified. The absorption calibration constant for diamond's 3107 cm−1 absorption line is 386 ± 64 ppb cm2. The corresponding cross-section per one H defect σ3107 (cm2) = (9.34 ± 1.25) × 10−18 /Γ (cm−1), Γ is the full width at half maximum (FWHM) of the 3107 cm−1 absorption line. Based on a widely accepted interpretation that the H defect resulting in the 3107 cm−1 IR absorption peak in diamonds is the N3VH defect, the values of the obtained calibration constant and cross-section have been assigned to the N3VH defect in diamond. The equations relating concentration of the N3VH defect ([N3VH]) with the 3107 cm−1 IR absorption line integrated intensity (I3107) and intensity (α3107) are as follows: [N3VH] (ppb) = (386 ± 64) I3107; [N3VH] (ppm) = (0.607 ± 0.080) α3107 (cm−1)Γ (cm−1). Hydrogen impurities that do not contribute to the IR absorption at the 3107 cm−1 peak were detected in all studied diamonds.

Role of chalcogen vacancies and hydrogen in the optical and electrical properties of bulk transition-metal dichalcogenides

Like in any other semiconductor, point defects in transition-metal dichalcogenides (TMDs) are expected to strongly impact their electronic and optical properties. However, identifying defects in these layered two-dimensional materials has been quite challenging with controversial conclusions despite the extensive literature in the past decade. Using first-principles calculations, we revisit the role of chalcogen vacancies and hydrogen impurity in bulk TMDs, reporting formation energies and thermodynamic and optical transition levels. We show that the S vacancy can explain recently observed cathodoluminescence spectra of MoS2 flakes and predict similar optical levels in the other TMDs. In the case of the H impurity, we find it more stable sitting on an interstitial site in the Mo plane, acting as a shallow donor, and possibly explaining the often observed n-type conductivity in some TMDs. We also predict the frequencies of the local vibration modes for the H impurity, aiding its identification through Raman or infrared spectroscopy.

Quantum size effect on discrete states of a hydrogenic impurity in a core/shell nanowire

The hydrogenic impurity states in a core/shell nanowire is studied by a variational method combined with a finite-difference algorithm. The quantum size effect on the wavefunction localization and energy levels at the ground state and lowing-excited eigenstates are analyzed by changing the core radius or shell composition. The transition from discrete states (confined) to extended states (continuum) will occur if changing the core radius or shell composition to a certain critical value. The ground-state binding energy of the hydrogenic impurity in the core/shell nanowire shows different variation trends with radius and composition.

The effect of pressure on the thermodynamic properties of hydrogenic impurity in the GaAs semiconductor quantum well

ABSTRACT Studying the thermodynamic properties of hydrogen impurity in low-dimensional nanostructures under high-pressure environment is crucial for understanding the optical property and thermal excitation behaviour of semiconductor material. Here, we extensively explore the effect of pressure on thermodynamic properties, specifically, the average energy, free energy, entropy, and heat capacity of one-dimensional (1-D) hydrogenic impurity in GaAs semiconductor quantum well. Our findings reveal some novel phenomenon in the thermodynamic properties of hydrogenic impurity as pressure increases in the GaAs quantum well. Remarkably, at a constant temperature, both the average energy and free energy of hydrogenic impurity decrease as pressure rises, while entropy increases with increasing pressure. Intriguingly, the heat capacity shows distinct behaviour with varying pressure for different sizes of the quantum well. For very small size of the quantum well, the heat capacity increases with increasing pressure. However, for larger size of the quantum wells, the variation of heat capacity with pressure becomes irregular, showing a changeover from an increase to a decrease in response to increasing pressure. This research presents a pioneering method that employs pressure as a versatile tool for modulating the thermodynamic properties of hydrogenic impurity states in the nanostructures, and has some guidance for the preparation and synthesis of semiconductor devices.

Effects of surface curvature and electric field on electronic and optical properties of an off-center hydrogenic donor impurity in 2D nanostructures

Effects of surface curvature and electric field on electronic and optical properties of an off-center hydrogenic donor impurity in 2D nanostructures

Development of an online hydrogen fuel quality analyzer with gas chromatography-pulsed discharge helium ionization detector for applying hydrogen infrastructures.

Hydrogen fuel, which is essential for the hydrogen economy, including hydrogen cell vehicles, must be of high quality for optimal hydrogen cell use. Currently, hydrogen fuel quality control is mainly done by offline analysis with periodic sampling. However, with the anticipated surge in hydrogen charging stations, there's a pressing need for cost-effective, high-throughput online analysis systems. Additionally, the miniaturization of these analytical instruments for field application is also a challenge. In this study, we present a compact, real-time hydrogen fuel analyzer based on gas chromatography with a pulsed discharge helium ionization detector. Its dual-column system efficiently analyzes major impurities in hydrogen fuel in less than 30 min. Indicator species (CO, CO2, CH4, O2, N2, and additional hydrogen sulfide [H2S]) are determined by examining hydrogen production and supply processes. The analyzer's measurement capability is consistent with µmol/mol-level analysis, providing valuable real-time information for hydrogen infrastructure managers. Additionally, it can analyze H2S, a crucial marker of sulfur compounds acting as catalytic poisons in fuel cells. This real-time analyzer offers efficient, informed decision-making support for hydrogen infrastructure managers, enhancing the overall reliability of hydrogen fuel in fuel-cell electric vehicles.

A theoretical study of the effects of uniaxial stress and spatial dielectric functions on the density of states of shallow donor impurities in a GaAs quantum well dot of circular geometry

In the present work, we have carried out a comparative study of the effects of uniaxial stress and spatial dielectric functions on the density of impurity states (DOIS) of shallow donor impurities in a GaAs quantum well dot of circular cross-section. Using a trial wave function in the effective mass approximation, we carried out calculations for a range of binding energies of hydrogenic (dielectric constant) and non-hydrogenic (spatial dielectric functions) donors for various applied uniaxial stress and for different uniaxial lengths of the quantum dot. Our results show that, for a constant axial length of the quantum dot and constant uniaxial stress, the DOIS for the donor impurity is markedly enhanced for the non-hydrogenic donor impurity over that for purely hydrogenic donor impurity. At constant axial length, the applied uniaxial stress enhances the DOIS in both cases. The density of impurity states has also been studied for a constant applied uniaxial stress for different axial lengths of the quantum dot. Here, again, the DOIS increases with increasing axial length of the quantum dot. In fact, the enhanced DOIS is observed throughout the range of binding energies considered. These results show that not only does the DOIS vary with the applied uniaxial stress and spatial dielectric functions they are also different for various axial lengths of the quantum dot. These findings indicate that is important to take into account the effect of applied uniaxial stress and spatial dielectric functions when performing experimental studies of electronic, optical and transport properties of such nanostructures as quantum dots.

Effects of electric and magnetic fields on the electronic properties in the asymmetrical biconvex lens-shaped GaAs/GaAlAs quantum dots

Theoretical investigation of electronic properties in asymmetric biconvex lens-shaped GaAs/GaAlAs quantum dots is considered in the presence of the external magnetic and electric fields. In addition, the effects of the dot size and the asymmetry of the structure on the electronic properties are also investigated. The shape of this quantum dot corresponds to the intersection of two differently centered spheres. The energy levels and wave functions of the shallow hydrogenic impurity in the structure with a finite potential are calculated numerically in cylindrical coordinates with the effective mass approach using a complex eigenvalue formalism through a two-dimensional axisymmetrical and three-dimensional finite element methods. The results reveal significant dependence of the calculated physical properties on lens dimensions, axial impurity position, and intensities of applied electric and magnetic fields.