Energies Of Carriers Research Articles

Unification of insertion and supercapacitive storage concepts: Storage profiles in titania

Insertion storage in battery electrodes and supercapacitive storage are typically considered to be independent phenomena and thus are dealt with in separate scientific communities. Using tailored experiments on titanium oxide thin films of various thicknesses, we demonstrate the simultaneous occurrence of both processes. For the interpretation of the entire storage profile encompassing both contributions, the (free) energies of the charge carriers in the mixed conductor and the neighboring phase are the only materials parameters required. The experimental results enable no less than a unification of insertion and supercapacitive storage, the first being dominant for thick films, the latter for thin films or negligible electronic conductivity. Therefore, the size of the storage medium and the nature of the current collecting phases can be used to tune power density versus energy density.

Structure, morphology and surface properties of α-lactose monohydrate in relation to its powder properties

The particulate properties of α-lactose monohydrate (αLMH), an excipient and carrier for pharmaceuticals, is important for the design, formulation and performance of a wide range of drug products. Here an integrated multi-scale workflow provides a detailed molecular and inter-molecular (synthonic) analysis of its crystal morphology, surface chemistry and surface energy. Predicted morphologies are validated in 3D through X-ray diffraction contrast tomography. Interestingly, from aqueous solution fastest growth is found to lie along the b-axis, i.e. the longest unit cell dimension of the αLMH crystal structure reflecting the greater opportunities for solvation on the prism compared to the capping faces leading to their slower relative growth rates. The tomahawk morphology reflects the presence of β-lactose which asymmetrically binds to the capping surfaces creating a polar morphology. The crystal lattice energy is dominated by van der Waals interactions (between lactose molecules) with electrostatic interactions contributing the remainder. Predicted total surface energies are in good agreement with those measured at high surface coverage by inverse gas chromatography, albeit their dispersive contributions are found to be higher than those measured. The calculated surface energies of crystal habit surfaces are not found to be significantly different between different crystal surfaces, consistent with αLMH's known homogeneous binding to drug molecules when formulated. Surface energies for different morphologies reveals crystals with the elongated crystal morphologies have lower surface energies compared to those with a triangular or tomahawk morphologies, correlating well with literature data that the surface energies of the lactose carriers are inversely proportional to their aerosol dispersion performance.

Simulation of quantum states in solid-state ferromagnetic nanostructures

Purpose of the article. Identification and analysis of mathematical expressions for the energy spectrum of charge carriers in nano-sized magnetic films of nickel and Ni-Cu (substrate), as well as NiO-Ni-Cu (substrate) structures.Methods. In this work, based on basic quantum mechanical concepts and taking into account the boundary conditions for coupled quantum wells, expressions for the energy spectrum of electrons are obtained. The ferrimagnetic properties of nickel are taken into account through the effective mass value. The solution of nonlinear equations that determine discrete energy levels was achieved by numerical methods using the Mathcad mathematical package.Results. Transcendental expressions for the energies of free charge carriers in quantum wells of ferromagnetic nickel films are obtained, and the influence of the position of nickel on the copper substrate is shown. It has been shown that the use of a copper substrate leads to an increase in the density of energy levels in the nickel nanofilm. The influence of the oxide layer on single-electron states in nanofilms of nickel and its oxide is considered within the framework of the Anderson model. Based on the numerical solution of the transcendental equations obtained in the work, the influence of the ratio of the thicknesses of a ferromagnetic metal and its oxide on the energy levels of electrons localized in the oxide layer is shown.Conclusions. The formulas presented in the work for the energy spectrum take into account the energy relief of a complex quantum well, the dimensions of the film, surface oxide, and the significant effective mass in the region of the ferromagnetic film. It has been shown that an increase in the effective mass in magnetic heterostructures leads to an increase in the electron density of states. It was found that the density of electronic states in the region of surface nickel oxide is practically independent of the thickness of the nickel film. The results and conclusions of the work can be used for theoretical prediction of the physical properties of magnetic nanostructures, in particular spintronic elements.

Frequency dispersion of dielectric coefficients of MnGaInTe4 crystals

The frequency and temperature dependences of the tangent of dielectric loss angle as well as the real and imaginary part of the dielectric constant of MnGaInTe4 crystals are investigated in the frequency range of 102 to 106 Hz. The experimental values of the studied characteristics are determined. The real and imaginary parts of the permittivity are found to undergo significant dispersion, which has a relaxation nature. The main type of dielectric losses in MnGaInTe4 crystals in the frequency range of 102 to 106 Hz are the electrical conductivity losses. The conductivity is characterized by a zone-hopping mechanism. The activation energies of charge carriers are determined.

Electric-Tree Resistant Performance and Thermal Charge-Carrier Dissipation Mechanism of Voltage Stabilizer-Modified EPDM

In order to improve electric-tree resistant performance and dielectric breakdown strength of ethylene-propylene-diene misch-polymere (EPDM) material used for cable accessory reinforce insulation, the two specific aromatic ketone compounds—vinylphenylacetone (VPE) and 4-propylene oxyxy-2-hydroxydibenzenone (AOHBP) are employed as two paradigms of voltage stabilizer for chemical-graft modifications. Electric-tree resistances and insulation performances of modified EPDM materials and their charge trapping mechanism of thermoelectron inhibitions are studied by the accelerated electric-tree aging experiments, alternating current (AC) dielectric breakdown tests, surface potential trap-level analyses and first-principles calculations. Both the two species of voltage stabilizers are effective for promoting electric-tree inception voltage and dielectric breakdown strength, leading to a high extension of electric-tree morphology and smaller dimension of electric-trees growth, in which AOHBP is more significant. The two species of voltage stabilizers have been successfully grafted onto EPDM molecular-chains in thermal-chemistry crosslinking reactions of EPDM, introducing multiple shallow levels of charge traps, which reduces the energy released by trapping charge carriers and thus alleviates electric-tree aging of EPDM. The AOHBP and VPE represent a high electron affinity and a small electronic energy gap, which is competent of assimilating the kinetic energies of hot charge carriers whilst restricting Auger electronic excitation. Especially, the benzene group in voltage stabilizer renders shallow level charge traps with a larger carrier capture cross-section than deep traps and simultaneously possesses the high atomic vibration frequencies similar as electronic-transition energies, which results in effective dissipation on the kinetic energies of hot charge carriers. This mechanism dominates to increase electric-tree resistance and insulation strength of EPDM. The present study proves the important role of voltage stabilizers in improving insulation performance of EPDM material, and reveals the refrigeration mechanism on hot charge carriers for restricting electric-tree growth, which provides a significant strategy of chemical modifications for developing high-insulation cable accessory materials.

Structure and dielectric properties of solid solutions Bi7−2xNd2xTi4NbO21(x = 0.0, 0.2, 0.4, 0.6, 0.8, 1.0)

The electrophysical and structural characteristics of bismuth titanate oxides of a number of phases of solid solutions of the Aurivillius phases Bi[Formula: see text]Nd[Formula: see text]Ti4[Formula: see text] ([Formula: see text] = 0.0, 0.2, 0.4, 0.6, 0.8, 1.0) having a layered structure of the perovskite type have been investigated. According to the XRD data, all studied compounds are single-phase and have a mixed-layer structure of Aurivillius phases ([Formula: see text] = 2.5) with a rhombic crystal lattice (space group I2cm, [Formula: see text] = 2). A relationship has been established between changes in the chemical composition of solid solutions and orthorhombic and tetragonal distortions of perovskite-like layers. The temperature dependences of the relative permittivity [Formula: see text]/[Formula: see text](T) are measured. It was found that the change in the phase transition temperature — Curie temperature [Formula: see text] synthesized Aurivillius phases Bi[Formula: see text]Nd[Formula: see text]Ti4[Formula: see text] ([Formula: see text] = 0.0, 0.2, 0.4, 0.6, 0.8, 1.0) has a close to linear dependence on the change in the parameter [Formula: see text]. The activation energies of charge carriers in different temperature ranges were calculated. It was found that three clearly defined temperature ranges with different activation energies can be distinguished, which is associated with the different nature of charge carriers in the studied solid solutions of the perovskite type. The effect of substitution of Nd[Formula: see text] ions for Bi[Formula: see text] ions is investigated.

Crystal structure and dielectric properties of layered perovskite-like solid solutions Bi3−x Gdx TiTaO9 (x = 0.0, 0.1, 0.2, 0.3) with high Curie temperature

The Aurivillius phases [Bi2O2][A[Formula: see text][Formula: see text]O[Formula: see text]] are well-known ferroelectrics with high Curie temperatures [Formula: see text]. High-temperature piezoceramics Bi[Formula: see text][Formula: see text]TiTaO9 (BGdTTa, [Formula: see text]= 0.0, 0.1, 0.2, 0.3) were prepared by a solid-state reaction method. The structural and electrophysical characteristics of BGdTTa ceramics have been studied. According to the data of powder X-ray diffraction, all the compounds are single-phase with the structures of two-layer Aurivillius phases ([Formula: see text] = 2) with the orthorhombic crystal lattice (space group A21am). The temperature dependence of the relative permittivity [Formula: see text]/[Formula: see text] ([Formula: see text] of the compounds was measured and showed that the Curie temperature [Formula: see text] of perovskite-like oxides Bi[Formula: see text][Formula: see text]TiTaO9 increases linearly with an increase in the substitution parameter [Formula: see text] to [Formula: see text] = 925[Formula: see text]C. The activation energies of charge carriers have been found in different temperature ranges.

Dielectric properties, relaxation and study of conduction process of Ba0.5Sr0.5Ti0.99Sn0.01O3 ceramics

Polycrystalline compound of Ba0.5Sr0.5Ti(1-x)SnxO3 (x = 0.01) prepared via solid-state reaction route was analyzed by XRD, SEM, dielectric and CIS examination of the sample. Study of XRD data confirmed the material to crystallize in cubic structure for the produced sample. The SEM micrograph depicted distributed grains with clear grain boundary. Loss tangent and dielectric constant variations were studied for frequency ranging from 1 kHz to 1 MHz and thermal range of room temperature (RT) to 400 °C. The loss tangent was found to be significantly less than Ba0.5Sr0.5TiO3. The presence of peak in loss tangent spectroscopy plot suggested dielectric relaxation occurring in the material within studied frequency range. Impedance spectroscopy data were analyzed in different formalism for the contribution of grain boundary and grain in conduction/relaxation process and the activation energies of charge carriers involved were estimated. These values suggested that conduction process is primarily dependent on oxygen vacancies. Jonscher’s power law defines the frequency dependant AC conductivity at different temperature values.

Investigation of relaxation phenomenon in lanthanum orthoferrite extracted through complex impedance and electric modulus spectroscopy

Impedance and electric modulus spectroscopy is exploited over a broad frequency and temperature range to find the relaxation phenomenon in LaFeO3 (LFO), which otherwise was concealed by the dc conductivity in dielectric ɛ*(ω) representation. The impedance measurements and the ac resistivity determined from Z′(ω) indicate that LFO is an insulator at room temperature and divulges the negative temperature coefficient of resistance. At higher temperatures, capacitive behavior flips to inductive behavior. The ac resistivity is exploited to determine the activation energy using the Arrhenius model. The relaxation peaks appear in the imaginary parts of electric modulus [M*(ω)] and impedance [Z(ω)], which have been exploited to determine the activation energy. The single distorted semicircle in the Nyquist and complex plots of electric modulus is evidence of the contribution of grains in the conduction process. At higher temperatures, data corresponding to the grain interior transform from an arc to a line with an intercept on the Z′(ω) axis and is parallel to the imaginary axis Z″(ω). Relaxation times calculated from the imaginary parts of impedance and electric modulus fit well in accordance with the Arrhenius law. Electron hopping, hole hopping, and oxygen vacancies play an important role in the dielectric response of grains. The relaxation frequencies of Z″(ω) and M″(ω) follow the sequence of scaling of magnitude of relaxation frequencies, i.e., fz′′≤fM′′. The separation of relaxation peaks of M″(ω) and Z″(ω) are indicative of a localized conduction process. The Giuntini law is applied to determine the hopping energies of charge carriers.

Structure and dielectric properties of solid solutions Bi7Ti4+xWxNb1−2x−0.1V0.1O21 (x=0.1−0.4)

The structural and electrophysical characteristics of a number of solid solutions of layered oxides of the perovskite-type Bi7[Formula: see text]Wx[Formula: see text][Formula: see text][Formula: see text] ([Formula: see text]) are studied. According to X-ray powder diffraction data, all the compounds studied are single-phase and have the structure of Aurivillius phases ([Formula: see text]) with a rhombic crystal lattice (space group I2[Formula: see text]cm, [Formula: see text]). Changes in tetragonal and rhombic distortions of perovskite-like layers in compounds were considered depending on their chemical composition. The temperature dependences of the relative permittivity [Formula: see text] (T) were measured. It was shown that the Curie temperature [Formula: see text] of the perovskite-type oxides Bi7[Formula: see text]Wx[Formula: see text][Formula: see text][Formula: see text] ([Formula: see text]) linearly decreases with increasing parameter [Formula: see text]. The activation energies of charge carriers were obtained in different temperature ranges. It was found that there are three temperature regions with very different activation energies due to the different nature of the charge carrier s in the studied compounds. The effect of substitution of [Formula: see text] ions by [Formula: see text] ions is investigated. It was found that for a number of compounds, the substitution of niobium ions by vanadium ions led to an increase in the dielectric constant and a decrease in the dielectric loss tangent.

Crystal structure and dielectric properties of layered perovskite-like solid solutions Bi3−xGdxTiNbO9 (x=0, 0.1, 0.2, 0.3) with high Curie temperature

The Aurivillius phases (APs) [Bi2O2][Formula: see text][[Formula: see text][Formula: see text]][Formula: see text] are well-known ferroelectrics with high Curie temperatures. High-temperature piezoceramics [Formula: see text]GdxTiNbO9(BiGdTiNb, [Formula: see text], 0.1, 0.2, 0.3) were prepared by a solid-state reaction method. The structural and electrophysical characteristics of BiGdTiNb ceramics have been studied. According to the data of powder X-ray diffraction, all the compounds are single-phase with the structures of two-layer APs ([Formula: see text]) with the orthorhombic crystal lattice (space group [Formula: see text]). The temperature dependence of the relative permittivity [Formula: see text] (T) of the compounds was measured and showed that the Curie temperature of perovskite-like oxides [Formula: see text]GdxTiNbO9 increases linearly with an increase in the substitution parameter [Formula: see text] to [Formula: see text]C. The activation energies of charge carriers have been found in different temperature ranges.

Enhanced Dissociation of Hot Excitons with an Applied Electric Field under Low-Power Photoexcitation in Two-Dimensional Perovskite Quantum Wells.

The dependence of photoluminescence (PL) on excitation power and the effect of an external electric field have been studied for a two-dimensional (2D) perovskite (C4H9NH3)2PbI4 thin-film sample. The efficiency of dissociation of hot excitons to produce free carriers was enhanced with a small excitation power because the relaxation of hot excitons to cold emissive excitons was slow, indicating that the thermal energies of hot carriers can be utilized in solar cells under weak photoirradiation. The dissociation was notably enhanced with an applied electric field, resulting in efficient field-induced quenching of the PL. The present results shed light on an application of 2D perovskite materials to photovoltaic (PV) devices with dim radiation, e.g., for indoor PV applications; the concept of electric field-assisted solar cells might be applicable to next-generation solar cells.

Polaronic interacceptor hopping transport in intrinsically doped nickel oxide

In this work, we revisit the issue of the nature of electronic transport in nickel oxide (NiO) and show that the widely used model of free small polaron hopping, initially raised to characterize transport in high-purity samples, is not appropriate for modeling intrinsically doped NiO. Instead, we present extensive evidence, collected by means of temperature- and frequency-dependent measurements of the electrical conductivity $\sigma$, that the model of polaronic inter-acceptor hopping can be used to consistently explain the electronic conduction process. In this framework, holes are localized to acceptors (Ni vacancies), forming a strongly bound, polaron-like state. They can only move through the film by hopping to a neighboring, at least partially unoccupied, acceptor. This renders the spatial overlap between neighboring polaronic wave functions a highly critical parameter. The signature of this process is the occurrence of two temperature regions of the DC conductivity, separated by about half the Debye temperature $\theta_D/2 \approx 200 K$. For $T > \theta_D/2$, holes are transferred by phonon-assisted hopping over the potential barrier between two sites, whereas phonon-assisted tunneling through the barrier dominates below that temperature. We also show that the degree of structural and electronic disorder plays a vital role in determining the characteristics of the transport process: high disorder leads to strong energetic broadening of the acceptor states such that hopping to more distant sites may be favored over transfer to nearest neighbors (variable range hopping). The assumption of high binding energies of the charge carriers at VNi is in accordance with the recent paradigm shift regarding the understanding of the electronic structure of NiO: holes doped into NiO couple to Ni 3d spins, thereby occupying deep polaron-like states within the band gap (Zhang-Rice bound doublets).

Study of Transfer Characteristics of a Molecular Electronic Sensor for Borehole Surveys at High Temperatures and Pressures

The paper considers the development and experimental study of the characteristics of a high-temperature motion parameter sensor based on molecular-electronic technology (MET) operating at elevated pressures. Studies were conducted in an extended temperature range (25–125 °C) with a static external pressure of up to 10 atm. A pilot plant based on a high-pressure chamber with the ability to output an electrical signal was specially designed and commissioned. A family of amplitude-frequency characteristics of a ME sensor in an extended temperature range was obtained for the first time. A theoretical model was constructed and verified to describe the transfer function of the sensor at high temperatures and pressures. The activation energies of active carriers were calculated, and a prediction was made about the possibility of using the developed devices for the needs of the oil and gas mining industries.

Electronic polarization in dipolar organic molecular semiconductors: The case study of 1,2,3,4-tetrafluoro-6,7-dimethylnaphthalene crystal

Electronic polarization has an important impact on the site energies of charge carriers that play a key role in determining the charge transport in organic semiconductors. Dipolar molecules have strong intermolecular interactions and widespread applications in organic optoelectronics. However, compared with nonpolar organic semiconductors, electronic polarization for dipolar systems has been rarely studied. Here, taking 1,2,3,4-tetrafluoro-6,7-dimethylnaphthalene as representative, we have calculated the electronic polarization energies of dipolar organic molecular crystals by means of a polarizable force-field method. Surprisingly, our results point to that the polarization energies for this dipolar system are similar to those of nonpolar systems. In addition, the π-π stack contributes only about 30%∼40% to the total polarization energy, thus the polarization effects along the three dimensions should be treated equally even for the one-dimensional stacking crystals.

Quantifying Wavelength-Dependent Plasmonic Hot Carrier Energy Distributions at Metal/Semiconductor Interfaces.

Hot carriers generated from the nonradiative decay of localized surface plasmons are capable of driving charge-transfer reactions at the surfaces of metal nanostructures. Photocatalytic devices utilizing plasmonic hot carriers are often based on metal nanoparticle/semiconductor heterostructures owing to their efficient electron-hole separation ability. The rapid thermalization of hot carriers generated at the metal nanoparticles yields a distribution of carrier energies that determines the capability of the photocatalytic device to drive redox reactions. Here, we quantify the thermalized hot carrier energy distribution generated at Au/TiO2 nanostructures using wavelength-dependent scanning electrochemical microscopy and a series of molecular probes with different redox potentials. We determine the quantum efficiencies and oxidizing power of the hot carriers from wavelength-dependent reaction rates and photocurrent across the metal/semiconductor interface. The wavelength-dependent reaction efficiency tracks the surface plasmon resonance spectrum of the Au nanoparticles, showing that the reaction is facilitated by plasmon excitation, while the responses from molecules with different redox potentials shed light on the energy distribution of the hot holes generated at metal nanoparticle/semiconductor heterostructures. The results provide important insight into the energies of the plasmon-generated hot carriers and quantum efficiencies of plasmonic photocatalytic devices.

Fine structure of the exciton absorption in semiconductor superlattices in crossed electric and magnetic fields

The exciton absorption coefficient is determined analytically for a semiconductor superlattice in crossed electric and magnetic fields, for the magnetic field being parallel and the electric field being perpendicular to the superlattice axis. Our investigation applies to the case where the magnetic length, while being much smaller than the exiton Bohr radius, considerably exceeds the superlattice period. The optical absorption in superlattices displays a spectral fine structure related to the sequences of exciton states bound whose energies are adjacent to the Landau energies of the charge carriers in the magnetic field. We study effects of external fields and of the center-of-mass exciton motion on the fine structure peak positions and oscillator strengths. In particular, we find that the inversion of the orientation of the external fields and of the in-plane total exciton momentum notably affects the absorption spectrum. Conditions for the experimental observation of the exciton absorption are discussed.

Explanation of Non-linear In-Plane Resistivity and Hall Coefficient in the Normal State of Cuprates: Polaronic Approach

We present a theoretical study of the in-plane resistivity ρ a b (T) and Hall coefficient R H (T) within the polaronic model and precursor pairing scenario by considering a two-component charge carrier picture in the normal state of high-temperature superconducting cuprates (HTSC). Here, we use a Boltzmann-equation approach and extended BCS-like model to compute ρ a b (T) and R H (T) in the τ-approximation. The opening of the pseudogap (PG) in the normal state of the cuprates should affect their transport properties. We have found that the transition to the PG regime and the effective conductivity of charge carriers in the normal state are responsible for the pronounced non-linear temperature dependence of ρ a b and R H . With the two-component model analysis, we conclude that the opening of the BCS-like PG, while the non-linear temperature dependence of ρ a b and R H could be understood as a consequence of pairing fluctuations in the PG state of cuprate superconductors. The calculated results for ρ a b (T) and R H (T) were compared with the experimental data obtained for various hole-doped cuprates. For all the considered cases, a good quantitative agreement was found between theory and experimental data. We also show that the energy scales of the binding energies of charge carriers are identified by PG crossover temperature on the cuprate phase diagram.

Molecular vibrations, activation energies of trapped carriers and additional structure in thermoluminescence of organic polymers

Manifestations of optical vibrations in thermoluminescence of organic polymers were observed. Thermoluminescence curves and Raman spectra of the polymers which have different degrees of ordering: poly(di-n-hexylsilane), poly(methylphenylsilane) and poly(di-n-penthylsilane) were measured and the features on thermoluminescence curves were observed. Activation energies of localized charge carriers were found by the fractional thermally stimulated luminescence in the 5–50K temperature range. The shape of the thermoluminescence curve was calculated in the model which assumed that the release of carriers from traps may be activated via the energy transfer from the vibrations to the carriers. The model explained the appearance of the features on thermoluminescence curves and the coincidence of the carriers’ activation energies with the vibration quanta. Thermoluminescence shows (and the calculations support this claim) that the decrease of the degree of the polymer ordering causes a decrease of the number the discrete values of activation energies and of the number of the features on thermoluminescence curves.

Quantum engineering of matter from the laboratory to the market: an interview with Dieter Bimberg and Kang Wang

Abstract Quantum dots introduce a new form of quantum engineering of materials properties based purely on size and dimensionality. Whereas we traditionally think of materials as having intrinsic properties such as strength, electrical conductivity and light absorption or emission spectra due to their composition and atomic-scale structure, when their size is very small, such properties can be altered by quantum-mechanical effects, for example due to confinement of the quantum wavefunctions that determine the energies of charge carriers like electrons. As it became possible in the 1990s to control the size of material structures with a precision of less than a nanometre in all three dimensions of space, quantum effects began to be exploited for technological applications. Quantum dots are particles with a nanoscale extent in three dimensions—in effect, tiny fragments of material, often made of one type of semiconductor embedded in another. Quantum dots in which the wavelength of absorption and fluorescent emission of light is tuned by the nanoparticle size are being explored for uses ranging from colour displays to biomedical imaging. Films of semiconducting materials thin enough to exhibit one-dimensional quantum-confinement effects, meanwhile, are routinely used to make efficient optical devices such as lasers. Such applications have depended on the availability of techniques for precise control of particle size, composition and thickness. NSR spoke to two leading researchers in this field of quantum engineering about its development and prospects. Dieter Bimberg is founding director of the Center of Nanophotonics at the Technical University of Berlin in Germany. He pioneered the use of quantum dots in photonic devices such as lasers and optical amplifiers, as well as developing non-volatile ‘dynamic’ random-access memories (DRAMs), which retain their information when the power is switched off. Kang Wang is a professor of electrical engineering at the University of California at Los Angeles, whose work on nanoscale quantum devices has focused on electronic and magnetic properties, and in particular on the development of non-volative RAMs and the manipulation and control of electron spin as a new parameter for information processing (a technology called spintronics).