Direct Current Electrical Conductivity Research Articles

Review of the second charged-particle transport coefficient code comparison workshop

We report the results of the second charged-particle transport coefficient code comparison workshop, which was held in Livermore, California on 24–27 July 2023. This workshop gathered theoretical, computational, and experimental scientists to assess the state of computational and experimental techniques for understanding charged-particle transport coefficients relevant to high-energy-density plasma science. Data for electronic and ionic transport coefficients, namely, the direct current electrical conductivity, electron thermal conductivity, ion shear viscosity, and ion thermal conductivity were computed and compared for multiple plasma conditions. Additional comparisons were carried out for electron–ion properties such as the electron–ion equilibration time and alpha particle stopping power. Overall, 39 participants submitted calculated results from 18 independent approaches, spanning methods from parameterized semi-empirical models to time-dependent density functional theory. In the cases studied here, we find significant differences—several orders of magnitude—between approaches, particularly at lower temperatures, and smaller differences—roughly a factor of five—among first-principles models. We investigate the origins of these differences through comparisons of underlying predictions of ionic and electronic structure. The results of this workshop help to identify plasma conditions where computationally inexpensive approaches are accurate, where computationally expensive models are required, and where experimental measurements will have high impact.

Enhancement of electrical conductivity of biopolymer by sulfur nanoparticle dispersion technique

AbstractPresent work reports the investigation of the effect of different percentages of nanosized elemental sulfur particle grown in a biopolymer matrix. Sulfur is known for treatment against bacterial infections as an antimicrobial agent from ages as elemental sulfur and sulfur‐rich compounds interact with biological systems. In‐situ growth of sulfur nanoparticles is processed by the passage of environment friendly hydrogen sulfide gas in hydrated solution of gum acacia biopolymer. Gum acacia is ion conducting, plant derived natural polymer. In this work, structural and morphological studies are examined by x‐ray diffraction and scanning electron microscopy. It is found that with increasing concentration of sulfur nanoparticles the spheroidal shaped nanostructures grow in size and approaches the micron realm. Electrical characterization of the nanostructure synthesized biopolymer is observed by varying frequency over a broad‐spectrum range. Direct current electrical conductivity is found to be enhanced by 40 times higher over pure specimen.

Ag-doped NiS nanocubes: Tailoring properties for optimal antibacterial performance

This study explores the synthesis of silver-doped nickel sulfide nano-cubes (Ni1-xAgxS: x= 0.00, 0.04, and 0.08) through a cost-effective hydrothermal process. X-ray diffraction analysis assured the presence of hexagonal NiS nanoparticles with fine crystallinity, with an estimated crystallite size of Ag-doped NiS ranges from 21.19 to 15.69 nm. A reduction in crystallite size was observed while including Ag ions along with enhancement in lattice constants for ‘a’ and ‘b’ from 3.416 Å to 3.424 Å and ‘c’ from 5.280 to 5.286 Å. The scanning electron microscopic images displayed cubic shaped agglomerated particles, that seemed quite suitable for antibacterial activity. The materials exhibit semiconducting behavior, as evidenced by increased direct current electrical conductivity with the rise in temperature. With increased silver content, the direct current electrical conductivity rises, and activation energy decreases from 0.246 to 0.213 eV. Dielectric characteristics, including dielectric constant, dielectric loss, and AC electrical conductivity, show a positive correlation with temperature, and all the aforementioned values elevates with systematic variation in Ag doping. The Agar well-diffusion method evaluates the antibacterial activity of un-doped and Ag-doped NiS nano-cubes against various pathogens, such as Gram-positive bacteria (M. luteus and S. aureus) and Gram-negative bacteria (E. coli and S. enterica), and significant inhibitory zones against all tested microbes, confirming the potential antibacterial efficacy. The Ag-doped NiS exhibited enhanced antibacterial efficiency. This research highlights Ag-doped NiS nano-cubes attributed with multifaceted functionalities, making them promising candidates for particular usage such as targeted drug delivery systems, antibacterial powder, wastewater treatment and pharmaceutical applications.

Excitation-wavelength-dependent photoluminescence/electrical conductivity of copper oxide nanorods

This research work reports the synthesis of copper (II) oxide (CuO) nanoparticles using the wet chemical co-precipitation method. The synthesised nanoparticles were characterised using ultraviolet–visible spectroscopy, X-ray diffraction, field emission scanning electron microscopy with energy-dispersive X-ray spectroscopy and high-resolution transmission electron microscopy in terms of absorption, crystal structure and size, morphology and elemental composition, and particle size. The existence of functional groups was verified by Fourier transform infrared spectroscopy. The synthesised copper (II) oxide nanoparticles showed an absorption peak at 397 nm, and a Tauc’s plot study showed a band-gap energy of 3.2 eV. The effects of varied excitation energies – namely, 3.81 and 3.54 eV – on the emission spectra of rod-shaped nanoparticles were assessed through photoluminescence spectroscopy, and the release of red, orange, green, violet and yellow colours was observed. The voltage–current characteristics of nanoparticle pellets were measured using a two-probe technique. The increase in the direct-current electrical conductivity of pellets heated at 100 and 200°C was ascertained. Overall, this research work provides valuable insights into the electronic properties of copper (II) oxide nanoparticles, which could have potential applications in various fields such as catalysis and electronics.

Fast and Uncooled Semiconducting Ca-Doped Y-Ba-Cu-O Thin Film-Based Thermal Sensors for Infrared.

YBa2Cu3O6+x (YBCO) cuprates are semiconductive when oxygen depleted (x < 0.5). They can be used for uncooled thermal detection in the near-infrared: (i) low temperature deposition on silicon substrates, leading to an amorphous phase (a-YBCO); (ii) pyroelectric properties exploited in thermal detectors offering both low noise and fast response above 1 MHz. However, a-YBCO films exhibit a small direct current (DC) electrical conductivity, with strong non-linearity of current-voltage plots. Calcium doping is well known for improving the transport properties of oxygen-rich YBCO films (x > 0.7). In this paper, we consider the performances of pyroelectric detectors made from calcium-doped (10 at. %) and undoped a-YBCO films. First, the surface microstructure, composition, and DC electrical properties of a-Y0.9Ca0.1Ba2Cu3O6+x films were investigated; then devices were tested at 850 nm wavelength and results were analyzed with an analytical model. A lower DC conductivity was measured for the calcium-doped material, which exhibited a slightly rougher surface, with copper-rich precipitates. The calcium-doped device exhibited a higher specific detectivity (D*=7.5×107 cm·Hz/W at 100 kHz) than the undoped device. Moreover, a shorter thermal time constant (<8 ns) was inferred as compared to the undoped device and commercially available pyroelectric sensors, thus paving the way to significant improvements for fast infrared imaging applications.

Insulation properties enhancement of crosslinked polyethylene by grafting electron‐buffering voltage stabilizers

AbstractGrafting a voltage stabilizer on molecular chains of cross‐linked polyethylene (XLPE) can effectively improve the materials' insulation properties. Four different samples (XLPE, XLPE grafted with the voltage stabilizer, low‐density polyethylene (LDPE) blended with the voltage stabilizer, and LDPE grafted with the voltage stabilizer) are prepared in this paper. Several physicochemical and dielectric tests are performed to investigate the properties of the samples. The results demonstrate that the m‐aminobenzoic acid is successfully grafted onto the XLPE molecular chain. Moreover, the crosslinking and grafting processes are equally important for enhancing the materials' performance of the XLPE. In addition, the grafted voltage stabilizer negligibly affects the gel content and thermal properties of XLPE. However, it increases the crystallinity but decreases the lamella thickness. Moreover, the XLPE grafted with a voltage stabilizer has lower direct current (DC) electrical conductivity, less aggregation of space charge, and higher DC breakdown strength. The trap distribution results indicate that the voltage stabilizer introduces shallow traps in the sample and the quantum chemical calculations describe that the material bandgap is decreased. Thus, the high‐energy charge carriers are buffered by the newly‐introduced traps and the functional groups, leading to the enhanced material properties of the XLPE.

Mechanochemical Synthesis and DC Electrical Conductivity of PANI-Based MWCNT Containing Nanocomposites with Te0 and Bi2Te3 Thermoelectric Nanophase

Nowadays, the search for the coupled polymer nanocomposite thermoelectrics that exhibit a high value of thermoelectric figure of merit (ZT) and similar behaviour of physical properties for the use as legs of thermoelectric cells is a current challenge. The direct current (DC) conductivity is one of the three important components of thermoelectric figure of merit. The aim of this study was to obtain PANI-based nanothermoelectrics with Te0 and Bi2Te3 nanoparticles and MWCNT by mechanochemical methodology and to investigate the dependency of their DC electrical conductivity on temperature in the 298–353 K range using the Arrhenius and Mott’s variable range hopping (VRH) models. Inorganic Te0 and Bi2Te3 nanoparticles were pre-synthesized by the available and environmentally friendly method using a commercial tellurium powder. The samples obtained were characterized by X-ray diffractometry (XRD), IR and UV-Vis spectroscopy. The XRD study of ES-PANI/Te0 (4.4 wt% Te0) and ES-PANI/Bi2Te3 (2.9 wt% Bi2Te3) nanocomposites found that the nanoparticle average size was 32 nm and 17 nm, respectively. The DC conductivity study of the samples with different nanophase content (2.1, 4.4, 10.2 wt% Te0, 1.5, 2.9, 7.3 wt% Bi2Te3, 1.5 wt% MWCNT) by the two points measurement method reveals the following: (a) the presence of inorganic nanophase reduces the conductivity compared to the matrix, (b) the addition of MWCNT in ES-PANI increases its electrical conductivity, (c) the conductivity of ES-PANI/Te0 as well as ES-PANI/Bi2Te3 nanocomposite rises with the increasing inorganic nanophase content, (d) the observed increase in the electrical conductivity of MWCNT-based nanocomposites with increasing inorganic nanophase content is interrupted by a characteristic area of decrease in its value at average values of inorganic nanoparticles content (at Te0 content of 4.4 wt%, at Bi2Te3 content of 2.9 wt%), (e) a similar DC conductivity behaviour in ES-PANI/Te0—ES-PANI/Bi2Te3 and ES-PANI/Te0-MWCNT—ES-PANI/Bi2Te3-MWCNT nanocomposite pairs is observed.

Eliminating Ambiguities in Electrical Measurements of Advanced Liquid Crystal Materials

Existing and future display and non-display applications of thermotropic liquid crystals rely on the development of new mesogenic materials. Electrical measurements of such materials determine their suitability for a specific application. In the case of molecular liquid crystals, their direct current (DC) electrical conductivity is caused by inorganic and/or organic ions typically present in small quantities even in highly purified materials. Important information about ions in liquid crystals can be obtained by measuring their DC electrical conductivity. Available experimental reports indicate that evaluation of the DC electrical conductivity of liquid crystals is a very non-trivial task as there are many ambiguities. In this paper, we discuss how to eliminate ambiguities in electrical measurements of liquid crystals by considering interactions between ions and substrates of a liquid crystal cell. In addition, we analyze factors affecting a proper evaluation of DC electrical conductivity of advanced multifunctional materials composed of liquid crystals and nanoparticles.

Preparation and properties of double percolated co-continuous PC/PET/MWCNT/GNP engineering polymer blend nanocomposites

This study reports on the preparation and characterization of nanocomposites based on polycarbonate (PC)/poly ethylene terephthalate (PET) blend containing low amounts of hybrid of multiwalled carbon nanotube (MWCNTs) and graphene nanoplates (GNPs) by melt mixing. To use double percolation mechanism, at first a co-continuous polymer blend was prepared and the influence of nanofiller content on morphology, electrical conductivity, rheological and mechanical properties of co-continuous PC/PET blend was investigated. Blend containing 60 wt. % PET showed co-continuous morphology as observed by scanning electron microscopy and it was found that co-continuity remained unchanged by the addition of nanofillers. The direct current (DC) electrical conductivity results showed a low electrical percolation threshold around 0.5 phr. The results obtained from differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA) showed an increase in thermal stability and crystallinity of nanocomposites. By increasing nanofiller amount, the storage modulus, loss modulus, and complex viscosity of samples increased as an indication of the strong network formation between nanofillers and polymer chains. The rheological percolation threshold was also found in the range of 2.5–3.5 phr of nanofillers. The tensile measurements results showed that the addition PC to PET increases the tensile strength of PET.

Insights into synergy-induced multifunctional property enhancement mechanisms in hybrid graphene nanoplatelet reinforced polymer composites

Carbon-based hybrid composites have the potential to simultaneously enhance multiple material functional properties, compared to traditional biphasic composites. In this work, we demonstrate how taking a combined hybrid and hierarchical approach (i.e., polypropylene (PP)-based composite with graphene nanoplatelets (GNPs) coated on glass fibers (GFs), as a secondary micro-sized filler) is effective in multifunctional enhancement, without compromising the composites’ physical properties and mechanical performance. It is demonstrated that the volume exclusion and curvature effects of the highly oriented GFs, produces interconnected GNP clusters with relatively lower interstitial space. Hence, up to 6 orders of magnitude increase in direct-current electrical conductivity of the hybrid composites with 10 vol% GF was observed, relative to its biphasic counterpart. Also, at the percolation region, the hybrid composites reinforced with 10 vol% GF, have demonstrated an approximate 723 % increase in real permittivity. These improvements result in a synergy-induced Ku-band electromagnetic interference shielding effectiveness (EMI SE) of 20.56 dB, which is 81 % higher than that of the biphasic counterpart. Thermal conductivity measurements also showed considerable synergistic effect between the two fillers, whereby the thermal conductivity of the biphasic nanocomposite with 10 vol% GNP increased from 0.67 to 1.09 W/m·K for the hybrid composite containing 10 vol% GF. Such enhancements are accompanied by an approximate 109 % improvement in tensile strength, proving the efficacy of the hybrid approach to simultaneously enhance multiple properties, thereby meeting the requirements for novel practical applications.

Multiphysics Experimental Approaches for Insight into the Hydrogen Bonded Structures of Ethylene Glycol and Glycerol Mixtures toward Green Solvent Technology

Alcohols and their mixtures are credited most important polar solvents for advances in pharmaceutical, chemical,biological, thermal, and material technologies. A rigorous study for the characterization of hydrogen bonded heterogeneousintermolecular structures that formed in a mixed solvent based on alcohols containing two and three hydroxyl groupsmolecules is crucial to specific technological and industrial applications. Hence, in this work, the multiphysics experimentalapproaches including the measurements of dielectric, electrical, viscous, acoustic, thermal, and optical properties are appliedand analyzed to confirm the behaviour of hydrogen bonded molecular structures of ethylene glycol (EG; dihydric alcohol)with glycerol (Gl; trihydric alcohol) over the entire concentration range of EG+Gl mixtures at 298.15 K. The static dielectricpermittivity, direct current electrical conductivity, low frequency relaxation time, and refractive index values of the EG+Glmixtures are reported. Additionally, dynamic viscosity, density, ultrasound velocity, adiabatic compressibility,intermolecular free length, acoustic impedance, free volume, Rao’s constant, Wada constant, and viscoacoustic relaxationtime of the EG+Gl mixtures are determined, and also explored their significance to these alcohols molecular interactions.Ultraviolet-visible range absorbance behaviour of the alcohol mixtures is characterized in detail and confirmed theelectronic transitions at higher energy ultraviolet radiations. The detailed analysis of all the experimental results along withthe consideration of excess properties evidenced the formation of heterogeneous intermolecular hydrogen bonded structuresin these Newtonian-type alcohols mixtures. A small to adequate variation in the thermodynamical and other investigatedproperties with the concentration variation showed that the EG+Gl mixture can be optimized as a green solvent according tothe prerequisite properties for huge advances in soft condensed matter technologies.

Effect of Ni2+ substitution on structural, magnetic and electrical traits of Ba1-xNixFe2O4

Nickel substituted Barium ferrites is synthesized by citrate gel method. Nickel which is transition metal used to tailor the properties of the Ba spinel ferrites. The characterization techniques such as thermogravimetry–differential thermal analysis (TG-DTA), X-ray diffraction (XRD), vibrating sample magnetometry (VSM), Fourier transform infrared spectroscopy (FTIR), ultra-violet diffuse-reflectance spectroscopy (UV-DRS), scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDX), transmission electron microscopy (TEM), Raman analysis and direct current (DC) electrical conductivity are used to investigate various properties. XRD and rietveld refinement confirmed the existence of orthorhombic as well as cubic phase with the decrease in lattice parameters in orthorhombic phase. FTIR spectra confirmed the presence of absorption bands for tetrahedral and octahedral sites. Tauc’s plots accredited the increase in band gap with increase in Ni content. The magnetic hysterisis loop exhibited large variation in coercivity and remanence. Increased Yafet-Kittel (Y-K) angle indicated redistribution of ions amongst the sites strenthening the A-B exchange interactions. DC electrical conductivity observed the conductive switching from n-type to p-type. Thermally activated charge carriers and hopping of electrons boost drift mobility. The activation energy of conduction is observed in the range of 0.40 to 0.85 eV. Raman peaks confirmed formation of orthorhombic as well as cubic phase.

Spraying EPDM@NPs as an efficient strategy for polyethylene-based high-voltage insulation

The synthesizing strategy of grafting a structure similar to the polymer matrix on the nanoparticles (NPs) surface is highly efficient in improving the insulating properties of polymers. The comprehensive study consisting of quantum chemical simulations and electrical properties at elevated temperatures shows that under high temperatures and strong direct current (DC) electric fields, spraying an ultra-low concentration of 0.0001 wt% EPDM@ZnO at the cross-linked polyethylene (XLPE) interface can reduce its DC electrical conductivity, suppress space charge accumulation and increase the DC breakdown strength. The EPDM@ZnO inherits the hydrophobic properties of graft material EPDM. Adding very low concentrations such as 0.0001 wt% minimizes the impact on material cleanliness, i.e., impurities, and facilitates the uniform dispersion of nanoparticles in the host polyethylene matrix, thereby overcoming nanoparticle agglomeration. The reported synthesis strategy of nanoparticles and preparation process is believed to provide new insights for developing future ultra-high voltage direct current cables and can be widely applied to nano-polymer modification applications of coatings, structural materials, and interface materials.

Improving experimental procedures for assessing electrical properties of advanced liquid crystal materials

ABSTRACT Electrical measurements of liquid crystals are a standard part of their material characterisation. Typically, such measurements are carried out using a sandwich-like cell of a single thickness. In this paper, we show that interactions between ions and substrates of a liquid crystal cell result in the dependence of the direct current electrical conductivity of liquid crystal materials on the cell thickness. The obtained experimental results combined with modelling point to the existence of ions of several types and to the competition between ion-releasing and ion-trapping processes in liquid crystal cells. We also propose to use a multi-electrode twin-cell that allows the visualisation of the electric field screening effect in liquid crystals and its mitigation by means of ferroelectric nanoparticles.

Multiphysics of multifunctional nanofluids based on different oxides nanoparticles and glycerol fluid

Nanofluid (NF) materials consisting of glycerol (Gly) and different inorganic nano oxides (TiO2, ZnO, Al2O3, and SiO2 for the oxides concentration of 0.01 wt% to the weight of Gly base fluid) were prepared by a two-step method through ultrasonic cavitation process. These nanofluids were investigated by employing an X-ray diffractometer (XRD), ultraviolet–visible (UV–Vis) spectrophotometer, 20 Hz to 1 MHz frequency range dielectric relaxation spectroscopy (DRS), ultrasonic interferometer, and rotational viscometer. The multiphysics of these nanofluids includes structural and optical properties, dielectric permittivity, electrical conductivity, conductivity relaxation, ultrasound velocity, adiabatic compressibility, acoustic impedance, viscosity, density, thermal conductivity, and viscoacoustic relaxation were characterized. The XRD patterns identified monodispersed and stable suspensions of these different characteristic nanoparticles in the hydrogen-bonded 3D supramolecular structure of ultra-high viscous glycerol fluid which were supported by their UV–Vis absorbance analyses. The energy band gap values of the TiO2 and ZnO containing nanofluids were found primarily ruled by the characteristic optical properties of these oxides nanomaterials. The complex dielectric and various electrical functions studied at 25 °C revealed that the suspension of different oxide nanoparticles in the glycerol fluid increased the static permittivity whereas reduced the direct current electrical conductivity which showed strong conductivity relaxation process dependence. The rheological measurements of the formulated nanofluids were performed over a shear rate range of 0.4–40 s−1 at temperatures of 25–55 °C. The linear relationship between shear rate and shear stress and also the shear rate-independent viscosity revealed the Newtonian behaviour of these nanofluids. The shear viscosity non-linearly decreased with the increase of temperature and exhibited the Arrhenius behaviour for all different oxides containing Gly-based nanofluids. The acoustic parameters of the nanofluids were altered unevenly with types of nano oxides and inferred some structure-property correlations. The promising technologically useable properties of these nanofluids were expected to impact their potential applications in optoelectronics, UV-blocking, sensing, nanodielectrics, energy storing and electric insulation, heat transfer systems, and also in materials processing for the development of innovative soft condensed devices.

Ion-irradiation-induced effects on the surface characteristics of Ge–Bi–Se thin films

In this study, fabricated amorphous chalcogenide Ge10Se70Bi20 thin films were irradiated with nitrogen (N+), argon (Ar+), hydrogen (H+) and oxygen (O+) ion beams. The compositions of the pure and irradiated films were investigated using X-ray diffraction, which confirmed the amorphous structures of the pristine and the irradiated Ge10Se70Bi20 thin films. The optical parameters such as optical bandgap, absorption edge, Urbach energy, Tauc parameter and extinction coefficient of the unirradiated and irradiated films were determined using ultraviolet/visible spectroscopy. The energy gap was found to reduce from 1.355 eV for unirradiated Ge10Se70Bi20 to 1.02, 0.73, 0.60 and 0.51 eV after irradiation with nitrogen, argon, hydrogen and oxygen ion beams, respectively. Meanwhile, the band tail of Ge10Se70Bi20, which is 0.12 eV, increased to 0.16, 0.40, 0.45 and 0.48 eV after irradiation with nitrogen, argon, hydrogen and oxygen ion beams, respectively. In particular, the conductivity increased by two orders after the pristine film had been exposed to an oxygen beam. The direct current electrical conductivity of the pristine film increased from 1.5 × 10−7 to 1.4 × 10−5 Ω−1 cm−1 after irradiation with an oxygen ion beam. Furthermore, the activation energy and Mott’s parameters of the original and irradiated Ge10Se70Bi20 films were deduced. The reported modifications of the optical and electrical parameters suggest the use of irradiated Ge10Se70Bi20 thin films in important applications – for example, optical data storage and optoelectronic devices.

Transport properties of a 3-dimensional holographic effective theory with gauge-axion coupling

In this paper, we implement a 3-dimensional holographic effective theory with gauge-axion coupling. The analytical black hole solution is worked out. We investigate the Direct current (DC) thermoelectric conductivities. A novel property is that DC electric conductivity for vanishing gauge-axion coupling is temperature dependent. It is different from that of 4-dimensional axion model whose DC electric conductivity is temperature independent. In addition, the gauge-axion coupling induces a metal insulator transition (MIT) at zero temperature. The properties of other DC thermoelectric conductivities are also discussed. Moreover we find that the Wiedemann-Franz (WF) law is violated in our model.

Explanation of the Compensation Law and the Isokinetic Point in the Electrical Conduction of Crosslinked Polyethylene

Thermally activated direct current (DC) electrical conductivity in low-density polyethylene (LDPE) is known to be subject to the compensation law. Accordingly, the preexponential factor follows a specific relation with activation energy, reducing overall changes in conductivity. This relationship is governed by the Meyer-Neldel temperature. However, there is no published evidence for a corresponding isokinetic point, a temperature where the conductivity of all LDPE samples is the same. Here, it is determined that the compensation law applies to both DC and alternating current (AC) conduction for LDPE and for crosslinked polyethylene (XLPE) without an observed isokinetic point. The potential origins of compensation in polyethylene are discussed as well as reasons for similarity between LDPE and XLPE. It is observed that prolonged water exposure removed the compensation behavior. Meanwhile, preheating samples in the oven prior to measurements modifies the compensation behavior and reduced the spread around the isokinetic point. It is thus deduced that an isokinetic point can be observed in polyethylene but is obscured by contributions from water and other impurities.

Comparative Study on the Direct Current Electrical Conduction in Monolayer and Bilayer Plasma Polymerized Thin Films

A comparative study on the nature of direct current electrical conduction in the monolayer and bilayer plasma polymerized thin films has been discussed in this article. The plasma polymerized pyrrole (PPPy) monolayer, plasma polymerized N,N,3,5-tetramethylaniline (PPTMA) monolayer and plasma polymerized pyrrole-N,N,3,5-tetramethylaniline (PPPy-PPTMA) bilayer thin films were deposited at room temperature onto glass substrates by using a parallel plate capacitively coupled glow discharge reactor. The current density-voltage (J-V) characteristics and the conductivity-voltage (σ-V) characteristics have been studied to analyze the direct current conduction mechanism in PPPy, PPTMA monolayer and PPPy-PPTMA bilayer thin films. The observed results have been presented in this paper. The J-V and σ-V characteristics of PPPy and PPTMA monolayer thin films of different thicknesses indicated an increase in electrical conduction and also an increase in conductivity in the films of lower thicknesses. It is also observed that PPTMA thin films are more conductive than that of PPPy thin films. As a result the PPPy-PPTMA bilayer thin films of different thicknesses and different deposition time ratios indicated an increase in conductivity as the proportion of PPTMA is increased in the films. In addition to that, from the J-V and σ-V characteristics of PPPy, PPTMA and PPPy-PPTMA thin films of same thickness, it is observed that the current conduction and the conductivity in the bilayer thin films is less compared to the monolayer thin films. This unusual result has been explained by studying ideal and real bilayer thin films. It is also seen that in the low voltage region, the current conduction obeys Ohm’s law while the charge transport phenomenon appears to be the space charge limited conduction (SCLC) in the higher voltage regions.

Максимальная прыжковая электропроводность на постоянном токе по водородоподобным примесям в полупроводниках

A quasi-classical model for calculating DC (direct current) electrical conductivity in crystalline semiconductors with hydrogen-like impurities is developed at the transition from band conduction to impurity hopping conduction with decreasing temperature. This transition from the minimum band conductivity to the maximum hopping conductivity via impurities has the form of a characteristic ``kink'' in the temperature dependence of the electrical resistivity. The idea of the calculation is to preliminarily determine the transition temperature Tj using the standard approach within the framework of the two-band model. The shift of the top of the v-band (the bottom of the c-band) into the depth of the band gap due to the formation of a quasi-continuous band of allowed energy values from the excited states of acceptors (donors) is taken into account. This leads to a decrease in the value of a thermal ionization energy of the main shallow impurities due to a decrease in the maximum localization radius of a hole on an acceptor (an electron on a donor) with increasing impurity concentration. The values of the observed maximum hopping conductivity and drift hopping mobility corresponding to the temperature Tj are calculated. The numerical calculation within the framework of the proposed model is consistent with the known experimental data on the electrical conductivity and Hall coefficient of moderately compensated p-Ge crystals doped by neutron transmutation and non-intentionally compensated metallurgically doped n-Ge, as well as n- and p-Si crystals on the insulator side of the Mott insulator–metal concentration phase transition.