Dominant Charge Carriers Research Articles

Counter-thermal flow of holes in high-mobility LaNiO3 thin films

Measurements of electronic structure and theoretical models indicate that the Fermi surface of ${\mathrm{LaNiO}}_{3}$ (LNO) is predominantly holelike, with a small electron pocket. However, measurements of the Hall and Seebeck effects yield nominally opposite signs for the dominant charge carrier type, making charge transport in LNO puzzling. Here, we combine measurements of the Hall, Seebeck, and Nernst coefficients in high-mobility epitaxial LNO thin films, and resolve this puzzle by demonstrating that the negative Seebeck coefficient is generated by the diffusion of holes from cold to hot regions of LNO. We further examine this counter-thermal flow of holes by measuring the evolution of the Nernst coefficient from the diffusive to the ballistic regime, where the suppression of energy-dependent scattering leads to a reversal of the flow of holes.

Preparation and Electrochemical Properties of CaZr1-xScxO3-α

To develop a CaZrO3 -based, high-temperature proton conductor with high conductivity and resistance to the reduced atmosphere, we used Sc as a substitute for In as the dopant in CaZrO3. The electrical conductivity of CaZr1-xScxO3-α (x = 0.06, 0.12, 0.18, and 0.24) specimens was measured using the two-terminal ac method in an oxygen-rich atmosphere, hydrogen-rich atmosphere, and water vapor-rich atmosphere, at temperatures ranging from 573 K to 1473 K. The electrical conductivity of the CaZr1-xScxO3-α samples first increased and then decreased with the increase in amount of Sc2O3 doping, and it increased with an increase in temperature. The results of the H/D isotope effect measurement indicated that in the three different atmospheres, at temperatures from 573 K to 1273 K, protons are the dominant charge carrier. From the measurement of electromotive force, the theoretical (calculated) and the measured electromotive forces coincided. The proton mobility of CaZr1-xScxO3-α exceeded 90% in the hydrogen-rich atmosphere at temperatures from 573 K to 1273 K. At higher temperatures of 1373 K to 1473 K, positive holes were the dominant charge carrier in the oxygen-rich atmosphere, whereas the dominant charge carrier was vacancies in the hydrogen-rich atmosphere. These results agree with our previous studies.

Synthesis and characterization of photo-crosslinkable coumarin-containing polymer dielectric for organic transistors

Abstract Herein, a photo-crosslinkable coumarin-containing polymer, poly(7-(4-vinyl-benzyloxyl)-4-methylcoumarin) or PVBMC, was prepared, and its physicochemical and electrical properties as a gate dielectric in organic electronic devices, such as organic thin-film transistor (OTFT) and inverter, was evaluated. The crosslinking of PVBMC by exposure to UV light (365 nm) over time was characterized using Fourier-transform IR and UV–visible spectroscopy. The measured capacitance of the cross-linked PVBMC thin film in a metal-insulator-metal-type capacitor was as high as 36.4 pF/mm2. Pentacene-based OTFT and load-type inverter with the cross-linked PVBMC gate dielectric were prepared, and their electrical responses were evaluated under ambient conditions. The OTFT showed dominant hole charge carrier transport behavior with a field-effect mobility of 1.52 × 10−1 cm2/Vs and negligible hysteresis. The load-type inverter based on the OTFT exhibited moderate static and dynamic switching responses to the applied electrical pulse. These results suggest the potential application of photo-crosslinked PVBMC as a gate dielectric in the fabrication of high-performance OTFT-based devices.

Influence of texture on DC conductivity and dimensional changes of kaolin and illitic clay

The influence of the technological texture on the DC conductivity of an illitic clay and kaolin was studied. Textured samples were prepared by layering a wet plastic mass made from distilled water and clay. Anisotropy of the samples was assessed by studying the DC conductivity and dimensional changes as functions of temperature in parallel and perpendicular directions to the basal planes of illite and kaolinite crystals. It was found that the shrinkage of the samples after firing is more significant in the direction perpendicular to the basal planes. The DC conductivity both in the illitic clay and kaolin is higher parallel to the basal planes of illite or kaolinite crystals than perpendicular to them. In both materials, the dominant charge carriers are K+ and Na+ ions, complemented by H+ and OH– ions during the removal of the physically bound water and dehydroxylation. The influence of the texture remains observable in the kaolin samples even after a high-temperature treatment (1200 °C), contrary to the illitic clay where this influence is suppressed by the high amount of the glassy phase (~80 mass %) after the thermal treatment at temperatures above 1000 °C. Compared to the illitic clay, the influence of the technological texture on the DC conductivity of kaolin is more significant.

A systematic study on effect of electron beam irradiation on electrical properties and thermopower of RE0.8Sr0.2CoO3 (RE=La, Pr) cobaltites

The effect of electron beam (e-beam) irradiation on the crystal structure and transport properties of polycrystalline samples of La0.8Sr0.2CoO3 (LSCO) and Pr0.8Sr0.2CoO3 (PSCO) cobaltites is reported in this communication. The of X-ray diffraction data reveals that the pristine and irradiated compounds of LSCO and PSCO samples are single phased having rhombohedral structure with R-3C space group. It is noticed that the crystal structure is preserved even after irradiation. Nonetheless the unit cell parameters are slightly altered when exposed to e-beam. The resistivity patterns of LSCO and PSCO samples demonstrate the occurrence of semiconducting behavior over the measured temperature range of 10–300 K. From the analysis of the temperature dependent resistivity data on the bulk samples, it is seen that small polaron hopping (SPH) mechanism is more dominating in the high temperature region of the pristine sample as compared to e-beam irradiated samples of LSCO and PSCO. The Seebeck coefficient (S) data of all the batches of LSCO and PSCO samples predominantly display positive values over a vast temperature region, indicating that holes are the dominant charge carriers. The investigation of S measurements confirms the validity of SPH mechanism in the high temperature region.

Influence of Al doping on the magnetoresistance and transport properties of LaBaMnAlO (0 ≤ x ≤ 0.15) manganites

Abstract This report presents the structural, magnetoresistance, electrical and thermal transport properties of Aluminium substituted La 0.7 Ba 0.3 Mn 1−x Al x O 3 (0 ≤ x ≤ 0.15) compounds synthesized by solid state reaction method. To obtain crystallographic parameters, the X-ray diffraction patterns are fitted in R-3c space group with Rietveld refinement method. The resistivity and magneto-transport measurements are performed using standard four-probe assembly with and without magnetic fields. The peak resistivity ρ peak is noted at Metal-Insulator Transition temperature ( T MI ) and lowering in T MI is observed for higher concentrations of Al 3+ . The resistivity data have been analyzed in two parts. Firstly, in the metallic region below T MI the resistivity data is fitted with three degree polynomial. Secondly, in the semiconducting region above T MI data have been fitted with Variable Range Hopping (VRH) and Small Polaron Hopping (SPH) models. The Seebeck coefficients found to be positive throughout the temperature range (10 K–300 K) with holes as dominating charge carriers. Similar to the resistivity profile, in metallic region the thermo-power is explained with qualitative model based on diffusion, magnon-drag, phonon-drag and spin fluctuation contributions whereas the semiconducting region is explained with small polaron hopping model.

C60 Concentration Influence on MEH-PPV:C60 Bulk Heterojunction-Based Schottky Devices

We have investigated the effect of C60 concentration on the performance of poly[2-methoxy-5-(2′-ethylhexoxy-p-phenylene vinylene] (MEH-PPV):C60 blend-based Schottky barrier-based devices. Incorporation of C60 in MEH-PPV leads to a red shift and the reduction of intensity in MEH-PPV absorption spectra. The appearance of a C60 characteristic band in the Raman spectra of the composites indicates the presence of C60 in the blends. A FESEM study reveals that the addition of C60 significantly modifies the surface morphology of the blend films. However, higher concentrations (> 5 wt.%) results in agglomeration of C60 particles. Dark I–V measurements allow us to extract various diode parameters including barrier height, ideality factor, and saturation current. Profound variations have been observed in the dominant charge carrier transport mechanism for different C60 concentrations. A photoresponse study demonstrates the enhancement in the photocurrent with the increase in the C60 concentration up to 5 wt.%. Beyond this concentration, agglomeration impedes exciton dissociation and charge transport, which results in a decrease in the photocurrent. Finally, an impedance spectroscopy analysis has been extensively carried out to estimate the internal device parameters, such as junction resistance, capacitance and carrier lifetime. The correlation between these parameters and I–V curves has been established.

Effect of Tb-doped Concentration Variation on the Electrical and Dielectric Properties of CaF₂ Nanoparticles.

Calcium fluoride (CaF2) nanoparticles with various terbium (Tb) doping concentrations were investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM), and alternating current (AC) impedance measurement. The original shape and structure of CaF2 nanoparticles were retained after doping. In all the samples, the dominant charge carriers were electrons, and the F− ion transference number increased with increasing Tb concentration. The defects in the grain region considerably contributed to the electron transportation process. When the Tb concentration was less than 3%, the effect of the ionic radius variation dominated and led to the diffusion of the F− ions and facilitated electron transportation. When the Tb concentration was greater than 3%, the increasing deformation potential scattering dominated, impeding F− ion diffusion and electron transportation. The substitution of Ca2+ by Tb3+ enables the electron and ion hopping in CaF2 nanocrystals, resulting in increased permittivity.

Weak metal-metal transition in the vanadium oxytelluride Rb1−δV2Te2O

We report the synthesis, crystal structure, physical properties, and first-principles calculations of a vanadium-based oxytelluride Rb$_{1-\delta}$V$_2$Te$_2$O ($\delta\approx0.2$). The crystal structure bears two-dimensional V$_2$O square nets sandwiched with tellurium layers, mimicking the structural motifs of cuprate and iron-based superconductors. The material exhibits metallic conductivity with dominant hole-type charge carriers. A weak metal-to-metal transition takes place at $\sim$100 K, which is conformably characterized by a slight kink/hump in the electrical resistivity, jumps in the Hall and Seebeck coefficients, a minute drop in the magnetic susceptibility, and a small peak in the heat capacity. Neither Bragg-peak splitting nor superlattice reflections can be detected within the resolution of conventional x-ray diffractions. The band-structure calculations show that V-3$d$ orbitals dominate the electronic states at around Fermi energy where a $d_{yz}/d_{xz}$ orbital polarization shows up. There are three Fermi-surface sheets that seem unfavorable for nesting. Our results suggest an orbital or spin-density-wave order for the low-temperature state and, upon suppression of the competing order, emergence of superconductivity could be expected.

In-situ observation of oxygen mobility and abnormal lattice expansion in ceria during flash sintering

Flash sintering has been shown to be an effective method of sintering for many types of ceramics. However, the characteristics of flash sintering for each type of ceramic varies. When ionically conducting ceramics are sintered under a DC electric field, a strong dependence of densification with respect to position is observed. Microstructural analysis of the effect of electric field on oxygen ion conductors shows non-stoichiometry (oxygen deficiency) at the cathode which continues to build up over time under flash. In oxygen ion conductors, dominant charge carriers during flash are oxygen ions and the final density of the specimen is related to the availability of oxygen. This effect is no longer evident when using an AC power supply. Thus, use of AC instead of DC electric field is preferable for flash sintering of ionically conducting ceramics.

A Decade of Iontronic Delivery Devices

AbstractIn contrast to electronic systems, biology rarely uses electrons as the signal to regulate functions, but rather ions and molecules of varying size. Due to the unique combination of both electronic and ionic/molecular conductivity in conjugated polymers and polyelectrolytes, these materials have emerged as an excellent tool for translating signals between these two realms, hence the field of organic bioelectronics. Since organic bioelectronics relies on the electron‐mediated transport and compensation of ions (or the ion‐mediated transport and compensation of electrons), a great deal of effort has been devoted to the development of so‐called “iontronic” components to effect precise substance delivery/transport, that is, components where ions are the dominant charge carrier and where ionic–electronic coupling defines device functionality. This effort has resulted in a range of technologies including ionic resistors, diodes, transistors, and basic logic circuits for the precisely controlled transport and delivery of biologically active chemicals. This Research News article presents a brief overview of some of these “ion pumping” technologies, how they have evolved over the last decade, and a discussion of applications in vitro, in vivo, and in plantae.

Temperature dependence of the AC conductivity of illitic clay

Electrical conductivity measurement was used to characterize thermophysical processes occurring in illitic clay during firing. In this study, illitic clay was subjected to heating up to 1100 °C. The AC conductivity was measured at 10 different frequencies, ranging from 500 Hz up to 2 MHz. In the low-temperature interval (<250 °C) and during dehydroxylation (from 450 °C to 750 °C), H+ and OH– ions were the dominant charge carriers. Above 600 °C, the mobility of alkali ions was high enough to enable them to contribute to conductivity. Formation of glassy phase at high temperature rapidly increases conductivity. The conduction activation energies (EA) were calculated during a second firing. Above 350 °C, the values of EA lay in the interval between 0.79 eV (500 Hz) and 0.66 eV (2 MHz), which correspond to the conduction EA of alkali ions in an amorphous matrix. The responsible conduction mechanism was identified to be ion hopping.

CdS/Low-Band-Gap Kesterite Thin-Film Solar Cell Absorber Heterojunction: Energy Level Alignment and Dominant Recombination Process

The chemical and electronic interface structure (including energy level alignment) between wet-chemical deposited CdS and low-band-gap Cu2ZnSn(S,Se)4 (CZTSSe) thin-film solar cell absorbers was studied using direct and inverse photoemission. Complementarily, the activation energy (Ea) of the dominant charge carrier recombination process of related solar cell devices was derived by temperature-dependent current–voltage [I(V,T)] measurements. We find the CZTSSe surface to be free of any significant amount of sulfur and the formation of Cd–Se bonds at the interface. A small, positive (“spike”-like) conduction band offset of 0.21 ± 0.28 eV between CZTSSe and CdS was measured. In conjunction with the I(V,T) derived Ea of 1.09 ± 0.07 eV, which is in excellent agreement with the CZTSSe bulk band-gap energy of 1.07 eV, this reveals that high-rate charge carrier recombination at the CdS/CZTSSe interface can mainly be excluded as the performance-limiting factor in corresponding solar cells.

Fermi-level tuning of the Dirac surface state in (Bi1−xSbx)2Se3 thin films

We report on the electronic states and the transport properties of three-dimensional topological insulator (Bi1−xSbx)2Se3 ternary alloy thin films grown on an isostructural Bi2Se3 buffer layer on InP substrates. By angle-resolved photoemission spectroscopy, we clearly detected Dirac surface states with a large bulk band gap of 0.2–0.3 eV in the (Bi1−xSbx)2Se3 film with x = 0.70. In addition, we observed by Hall effect measurements that the dominant charge carrier converts from electron (n-type) to hole (p-type) at around x = 0.7, indicating that the Fermi level can be controlled across the Dirac point. Indeed, the carrier transport was shown to be governed by Dirac surface state in 0.63 ⩽ x ⩽ 0.75. These features suggest that Fermi-level tunable (Bi1−xSbx)2Se3-based heterostructures provide a platform for extracting exotic topological phenomena.

Influence of anisotropy on the electrical conductivity and diffusion coefficient of dry K-feldspar: Implications of the mechanism of conduction**Project supported by the Strategic Priority Research Program (B) of the Chinese Academy of Sciences (CAS) (Grant No. XDB 18010401), the Key Research Program of Frontier Sciences of CAS (Grant No. QYZDB-SSW-DQC009), the “135” Program of the Institute of Geochemistry of CAS,

The electrical conductivities of single-crystal K-feldspar along three different crystallographic directions are investigated by the Solartron-1260 Impedance/Gain-phase analyzer at 873 K–1223 K and 1.0 GPa–3.0 GPa in a frequency range of 10−1 Hz–106 Hz. The measured electrical conductivity along the [001] axis direction decreases with increasing pressure, and the activation energy and activation volume of charge carriers are determined to be 1.04 ± 0.06 eV and 2.51 ± 0.19 cm3/mole, respectively. The electrical conductivity of K-feldspar is highly anisotropic, and its value along the [001] axis is approximately three times higher than that along the [100] axis. At 2.0 GPa, the diffusion coefficient of ionic potassium is obtained from the electrical conductivity data using the Nernst–Einstein equation. The measured electrical conductivity and calculated diffusion coefficient of potassium suggest that the main conduction mechanism is of ionic conduction, therefore the dominant charge carrier is transferred between normal lattice potassium positions and adjacent interstitial sites along the thermally activated electric field.

Depolarization currents in illite

In ceramic materials, depolarization effects take place when an external electrical field is removed. Therefore, an understanding of mechanisms of polarization and depolarization is important for a more accurate control of furnace temperature and DC or pulse electrical field in flash sintering. In this paper, depolarization currents were measured in illitic clay samples in the temperature range 450–1100 °C for 150–300 min. The ionic component was dominant in these depolarization currents. Time dependences of depolarization currents suggested several depolarization mechanisms took place. They were caused by localized hopping or migration of K+, Na+, H+, and OH− ions, which were the dominant charge carriers in various temperature ranges, in the internal electric field induced by space charges at electrodes. Depolarization is a long-lasting process at high temperatures and influences the internal electrical field in ceramics.

New alkali-metal and 1,2-Diaminopropane intercalated superconductor Lix(C3H10N2)yFe2Se2 with [formula omitted] = 45 K

A new iron-based superconductor Lix(C3H10N2)yFe2Se2 was successfully synthesized via the novel ammonothermal technique. After post-annealing, the superconducting transition temperature Tc changes from 36 K to 45 K, which is confirmed by measurements of the magnetic susceptibility and the electrical resistivity. The powder X-ray diffraction (XRD) measurements have revealed that the crystal structure keeps the same after post-annealing at 130 °C for 10 h. Hall coefficient and magnetoresistance (MR) have been measured on the annealed samples, indicating the role of electrons as the dominant charge carriers.

Plasma conductivity as a probe for ambient air admixture in an atmospheric pressure plasma jet

By utilizing a fully floating double electrical probe system, the conductivity of a linear atmospheric pressure plasma jet, utilizing nitrogen as process gas, was measured. The floating probe makes it possible to measure currents in the nanoamp range, in an environment where capacitive coupling of the probes to the powered electrodes is on the order of several kilovolts. Using a chemical kinetic model, the production of reactive nitrogen oxide and hydrogen-containing species through admixture of ambient humid air is determined and compared to the measured gas conductivity. The chemical kinetic model predicts an enhanced diffusion coefficient for admixture of O2 and H2O from ambient air of 2.7 cm2 s−1, compared to a literature value of 0.21 cm2 s−1, which is attributed to rapid mixing between the plasma jets and the surrounding air. The dominant charge carriers contributing to the conductivity, aside from electrons, are NO+, NO2 − and NO3 −. Upon admixture of O2 and H2O, the dominant neutral products formed in the N2 plasma jet are O, NO and N2O, while O2(1Δg) singlet oxygen is the only dominant excited species.

Tailoring the Polarity of Charge Carriers in Graphene–Porphine–Graphene Molecular Junctions through Linkage Motifs

The ability to control the nature of charge carriers in single-molecule junctions is of paramount importance to the design of molecular scale CMOS logic circuits. One major limitation is that the present methods for tuning the polarity of the charge carriers in molecular junctions always rely on chemical modifications of certain moieties of the central molecule. Here we investigate this issue by computing the electronic transport properties of graphene–porphine–graphene (GPG) molecular junctions with the nonequilibrium Green’s function formalism combined with density functional theory. Our calculations show that the dominant charge carriers in these GPG junctions can be tuned from holes to electrons by simply varying the number of C–C covalent bonds formed at the porphine-graphene interfaces. When porphine is doubly fused to graphene, it exhibits p-type transport behavior; in contrast, the triply fused one displays n-type behavior. The cause of this is that distinct linkage motifs lead to a rearrangement of the molecular levels participating in charge transport. It is the first time that such effect is shown without using a chemical modification of the porphine. In addition, hydrogen tautomerization reaction in porphine induces a dramatic conductance switch for the doubly fused GPG junctions, suggesting promising applications of this system as two-level molecular switch or memory unit with binary digits.

Correlation between structural and transport properties of electron beam irradiated PrMnO3 compounds

The structural, electrical, magnetic, and thermal properties of electron beam (EB) irradiated PrMnO3 manganites were investigated in the present communication. X-ray diffraction data reveals that all samples are single phased with orthorhombic distorted structure (Pbnm). Furthermore, the diffracted data are analyzed in detail using Rietveld refinement technique. It is observed that the EB dosage feebly disturbs the MnO6 octahedra. The electrical resistivity of all the samples exhibits semiconducting behavior. Small polaron hopping model is conveniently employed to investigate the semiconducting nature of the pristine as well as EB irradiated samples. The Seebeck coefficient (S) of the pristine as well as the irradiated samples exhibit large positive values at lower temperatures, signifying holes as the dominant charge carriers. The analysis of Seebeck coefficient data confirms that the small polaron hopping mechanism assists the thermoelectric transport property in the high temperature region. The magnetic measurements confirm the existence of paramagnetic (PM) to ferromagnetic (FM) behavior for the pristine and irradiated samples. In the lower temperature regime, coexistence of FM clusters and AFM matrix is dominating. Thus, the complex magnetic behavior of the compound has been explained in terms of rearrangement of antiferromagnetically coupled ionic moments.