Direct Current Conductivity Research Articles

Electron tunneling spectroscopy of an anisotropic Kitaev quantum spin liquid sandwiched between superconductors

We present the electron tunneling transport and spectroscopic characters of a superconducting (SC) Josephson junction with a barrier of a single anisotropic Kitaev quantum spin liquid (QSL) layer. We find that the dynamical spin-correlation features are well reflected in the direct-current differential conductance $d{I}^{c}/dV$ of single-particle tunneling, including the unique spin gap and dressed itinerant Majorana dispersive band, in addition to an energy shift $2\mathrm{\ensuremath{\Delta}}$ from the two-SC-lead gap. From the spectral characters, we identify different topological quantum phases of the anisotropic Kitaev QSL. We also present the zero-voltage Josephson current ${I}^{s}$, which displays residual features of the anisotropic Kitaev QSL. These results pave a new path to measurement of dynamical spinon or Majorana fermion spectroscopy of Kitaev and other spin-liquid materials.

Understanding random telegraph noise in two-dimensional BP/ReS2 heterointerface

Black phosphorus (BP)-based broken gap heterojunctions have attracted significant attention mainly owing to its wide thickness-dependent Fermi level, offering opportunities to demonstrate various carrier transport characteristics and high performing optoelectronic applications. However, the interfacial effects on the carrier scattering mechanism of the two-dimensional (2D) broken gap heterojunctions are unclear. Herein, we discuss the origin of random telegraph noise of multilayer BP/ReS2 heterojunction diode, in particular, at the direct tunneling (DT) conduction regime. The gate-tunable diode characteristic of BP/ReS2 heterojunction allows one to unveil systematically the transition of the charge fluctuation mechanism from drift-diffusion to the DT regime. Unlike individual BP and ReS2 devices, the current noise histogram obtained from the BP/ReS2 heterojunction device exhibits exclusively two dominant peaks at the DT regime. We ascribed this distinct low-frequency noise feature representing the presence of random telegraph signal to the BP/ReS2 interfacial traps by taking into account of the inherent direct tunneling current conduction mechanism. In addition, the electrostatic bias-dependent power spectrum density manifests clearly that the dominant scattering mechanism is the carrier number fluctuation rather than tunneling barrier height fluctuation at the BP/ReS2 heterointerface. This study elucidates the carrier transport and the charge fluctuation mechanism at the 2D heterostructure interface.

Dielectric properties and dielectric relaxation process of polymethylphenylsiloxane/silicon dioxide nanocomposites

AbstractIn recent years, polysiloxane dielectric elastomers (DEs) have attracted extensive attention, but their low dielectric constant and electrical breakdown strength are the main factors that limit their wide application. In this work, we report the effects that a high content of hydrophobic silica has on the dielectric properties and dielectric relaxation behavior of polymethylphenylsiloxane (PMPS). Introducing a high content of hydrophobic silica into PMPS composites increased the dielectric constant of PMPS composites from 3.11 to 3.70 and the breakdown strength of PMPS composites from 35.31 to 42.66 kv/mm. The high content of hydrophobic silica is beneficial for restraining or delaying the occurrence of direct current (DC) conductivity and for effectively reducing the dielectric loss of composites in high temperature and low‐frequency regions. The high content of hydrophobic silica also produces interfacial polarization in the composites, and this increases the dielectric constant and dielectric loss in the high frequency and low‐temperature regions. The dielectric relaxation behavior of PMPS composites was studied in detail using broadband dielectric spectroscopy (BDS) and thermally stimulated depolarization current (TSDC) to better understand the effect of hydrophobic silica on dielectric properties. This work opens a new way to design and prepare polysiloxane‐based materials that have a high dielectric constant, low dielectric loss, and high breakdown strength.

Exclusion of DC conductivity effect from dielectric loss spectrum using Kramers–Kronig relations for evaluation of slow dynamics of water molecules

In the dielectric spectroscopy of aqueous systems containing ions, the dielectric loss spectrum is affected by the contribution of the direct current (DC) conductivity σ, which sometimes significantly overlaps the dielectric relaxations related to the slow dynamics of water molecules distributing in sub-GHz frequency range. We have demonstrated a practical procedure based on the Kramers–Kronig (KK) relations to exclude the contribution of DC conductivity from the experimentally obtained dielectric spectrum. Examples of the KK transform for the spectrum of ultrapure water and aqueous solution of protein (lysozyme) showed the feasibility of our method.

Introducing MWCNTs conductive network in polymer-derived SiCN ceramics for broadband electromagnetic wave absorption

In this work, a series of SiCN (MWCNTs) composite ceramics were prepared through polymer derivation method by adjusting the mass ratio of multiwalled carbon nanotubes (MWCNTs). On this basis, the influence of the addition amount of MWCNTs on reflection loss (RL), effective absorption bandwidth (EAB), electromagnetic parameters, direct current conductivity (σ), impedance matching parameter (Z) and attenuation coefficient (α) of composite ceramics was studied, the percolation threshold of MWCNTs addition amount was analyzed, and the electromagnetic wave (EMW) absorption performance and absorption mechanism of composite ceramics when the MWCNTs addition amount was fixed at the percolation threshold were discussed. The analysis shows that the conductive network composed by MWCNTs can significantly improve the EAB of ceramic samples. When the addition amount of MWCNTs reached 10 wt%, a conductive percolation state was achieved inside composite ceramics. At this time, the sample showed the optimal comprehensive EMW absorption performance: when the thickness was 1.7 mm, the minimum reflection loss (RLmin) was −21.7 dB, and its EAB reached 4.7 GHz. Compared with many similar magnetic SiCN-based composite ceramics or carbon-rich SiCN-based composite ceramics previously reported, the SiCN (MWCNTs) composite ceramics prepared in this work showed an obviously improved EAB under the condition of reduced thickness.

High surface wetting and conducting NiO/PANI nanocomposites as efficient electrode materials for supercapacitors

In this work, A series of facile citric acid-assisted gel combustion synthesized cubic structured nickel oxide nanoparticles (NiO NPs) filled polyaniline (PANI) were prepared via in-situ chemical oxidative polymerization method. The effect of different mass percent loaded NiO NPs on the PANI matrix and its crystalline structure, thermal stability, morphology, direct current (DC) conductivity, and electrolyte solvent affinity were investigated with the help of XRD, FTIR, TGA-DTA, SEM with EDS, UV–Vis absorption, current-voltage (I-V) characteristics, and contact angle (CA) measurements. Among all prepared nanocomposites 20 wt% loaded NiO NPs per anilinium chloride (C6H8ClN) weight (NiP3) showed the highest conductivity of about 6.09 × 10−2 S cm−1, good thermal stability over the range of 40–800 °C, and better electrolyte swelling ability with CA of 43.9°. So, this optimized nanocomposite was subjected to electrochemical analysis in 1 M HCl solution using cyclic voltammetry (CV), Galvanometric charge-discharge (GCD), electrochemical impedance spectroscopy (EIS). From 10 mV s−1 scan rated CV the Csp, Ea,c, and E(HE/OE)-pa for NiP3 voltammogram was found to be 480 F g−1, 0.4116 V, 0.7531 V respectively. Further, the results have confirmed that the specific capacitance of NiP3 was enhanced enormously than the pristine PANI.

Reverse bias dependent impedance and dielectric properties of Al/n-NC FeSi2/p-Si/Pd heterostructures formed by facing-targets sputtering

Al/n-NC FeSi2/p-Si/Pd heterostructures were formed by facing-targets sputtering. From the dark J-V results, the device showed rectifying action with leakage current. In this work, impedance spectroscopy was employed to study the electrochemical characteristics of the heterostructures, which were inspected within a frequency (f) range from 20 Hz to 2 MHz. The range of the biased voltage (V) was −1 V to 0 V. All plots of real and imaginary impedances possessed single semi-circular arcs for all bias V values. The relaxation time was 2.00 μs at −1 V, and it became faster at 0 V with 0.42 μs. The equivalent circuit for the heterostructures consisted of series resistance (Rs) combined with three sets of shunt circuits of resistance (Rp) and a constant phase element (CPE), representing grain, grain boundary, and junction, respectively. The simulated Rs and Rp values decreased, while all CPE values increased as the biased V increased. For the dielectric properties, the real permittivity (ε′) values of 86.70 at 0 V and 20.22 at −1 V were disclosed at 100 Hz; all ε′ values decreased as the f value was increased. The loss tangent revealed to be very high due to dielectric loss being much higher than ε′ values, indicating the device to be leaky. The alternating conductivities plotted against f started at a low level in low f zones and grew exponentially when f reached higher values for all V values. Direct current conductivity was observed at 1.66 × 10−4 S m−1 at 0 V, which reduced to 2.67 × 10−5 S m−1 at −1 V. The dimensionless exponent of the conductivity results was higher than 1, indicating the hopping movement within the local site.

In Situ Dielectric Spectroscopy Monitoring of Silica Nanoparticle Synthesis in Cationic Water-in-Oil Microemulsions.

In situ monitoring of microemulsion-based nanoparticle synthesis is significant for understanding the particle formation mechanism and for advancing controlled nanoparticle synthesis by this means. In this study, the processes of silica nanoparticle synthesis in a CTAB/n-hexanol/cyclohexane/ammonia microemulsion were monitored via dielectric spectroscopy in situ and in real time, with the influences of the water content and precursor concentration being considered. Two dielectric relaxations in addition to a water-induced one were observed in the frequency range of 1 MHz to 3 GHz, which persist throughout the synthesis processes. It is suggested that the lower-frequency relaxation is ascribed to interfacial polarization and the higher-frequency one is caused by the orientational polarization of the ion pair consisting of a counterion and a surfactant polar group. The latter and water-induced relaxations were found to be barely changed during the synthesis processes, while the former changes obviously with synthesis time. The evolution of the lower-frequency relaxation and direct current conductivity with synthesis time are presented and discussed, on the basis of which the particle formation process is inspected from a dielectric spectroscopic point of view.

Regimented Charge Transport Phenomena in Semiconductive Self-Assembled Rhenium Nanotubes

Photoconductivity, a crucial property, determines the potential of semiconductor materials for use in optoelectronic and photocatalytic device applications. The one-dimensional metal-organic nanotube semiconducting material [{Re(CO)3}6(bho)(phpy)6]n (MBT 1, where bho is benzene-1,2,3,4,5,6-hexaoate and phpy is 4-phenylpyridine) reported herein exhibits record photocurrent responses at a broad spectral range. MBT 1 is comprised of a unique nanotube structure that is composed of six rhenium sites, six 4-phenylpyridine ligands, and a benzene-1,2,3,4,5,6-hexaoate unit. The highly organized self-assembled molecular bamboo tube MBT 1 displays semiconducting characteristics with a low activation energy of 1.63 meV. The alternating current (AC) and direct current (DC) conductivities of pellet devices are approximately 10-4 S/cm. For a single-crystal device, DC conductivity was found to be 1.5 S/cm, an unprecedented 10 000 times higher. The bandgap of MBT 1 was determined to be 1.03 eV, consistent with the theoretically estimated value of 1.2 eV. Theoretical calculations suggest that the unique structural architecture of MBT 1 allows for effective charge transport, which is facilitated by the spatial separation of electrons and holes that MBT 1 contains. This also eliminates fast charge recombination. The findings are not only chemically and fundamentally important but also have great potential for applications in innovative nano-optoelectronics.

Terahertz nano-imaging of metal-insulator transition in Cd2Os2O7

The osmate pyrochlore Cd2Os2O7 supports an antiferromagnet insulator ground state with an all-in/all-out (AIAO) spin ordering at low temperature. Above 225 K, Cd2Os2O7 becomes a paramagnetic metal whereas the mechanism of this metal-to-insulator transition (MIT) remains elusive. In this letter, we use cryogenic near-field technique operating at terahertz frequencies to study the evolution of low-energy response across the MIT. We observed a systematic variation of the magnitude of nano-THz signal across the transition, consistent with the trend in the direct-current conductivity. Conducting domain walls that dominate the nano-scale landscape of the conductivity of a closely related AIAO system Nd2Ir2O7 are not apparent in Cd2Os2O7.

Frequency regulation in alternating current transportation properties for electron correlated rare-earth nickelates heterostructures

Although the rare-earth nickelate (ReNiO3) based heterostructures exhibit promising applications in logical devices based on the metal to insulator transition property that regulates abruptly their direct current transportations, their alternating current (ac) properties have not been fully studied. Herein, we demonstrate the frequency manipulation in the ac properties of various SmNiO3-based heterostructures as grown by pulsed laser deposition including SmNiO3/SrRuO3/SrTiO3, SmNiO3/SrRuO3/LaAlO3, and SmNiO3/SrRuO3/quartz. The activation energies as calculated from the dielectric relaxation process of the SmNiO3 heterostructure from the ac aspect are in consistence with the ones obtained from their direct current (dc) conduction. Assisted by the complex impedance equivalent circuit fitting, we further distinguished the dominance in carrier transportations associated with the intrinsic SmNiO3 crystal (SmNiO3/SrRuO3/SrTiO3), interfacial defects (SmNiO3/SrRuO3/LaAlO3), or grain boundaries (SmNiO3/SrRuO3/quartz). Owing to the strong Coulomb interaction between the electron carrier and NiO6 octahedron within the electron correlated insulating phase of SmNiO3, the temperature dependence in their real part impedance cross-linked at characteristic ranges of temperature and frequency. As a result, their electronic transportations gradually transit from the negative temperature coefficient resistance thermistor toward delta-tendency via elevating the input ac-frequency. This functionality is expected to enrich potential applications of SmNiO3-based correlated electronic devices in temperature sensing and control.

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.

Dynamic properties of two-dimensional latticed holographic system

We study the anisotropic properties of dynamical quantities: direct current (DC) conductivity, butterfly velocity, and charge diffusion. The anisotropy plays a crucial role in determining the phase structure of the two-lattice system. Even a small deviation from isotropy can lead to distinct phase structures, as well as the IR fixed points of our holographic systems. In particular, for anisotropic cases, the most important property is that the IR fixed point can be non-AdS2 × ℝ2 even for metallic phases. As that of a one-lattice system, the butterfly velocity and the charge diffusion can also diagnose the quantum phase transition (QPT) in this two-dimensional anisotropic latticed system.

Structural, magnetic and electrical properties of La1-xMgxFeO3 perovskites

In this study, we synthesized La 1-x Mg x FeO 3 (x = 0.1, 0.2, and 0.3) powdered ceramics using sol − gel and sintering methods and their structure, magnetic and electrical properties have been investigated. All samples showed the Pbnm single phase, and structural analyses revealed a lattice distortion due to the addition of Mg that increases with increasing Mg content. Transmission electron microscopy revealed a decrease in particle size with increasing Mg content. The M − H hysteresis loops of the samples revealed that the samples with Mg substitution at the La site exhibits weak ferromagnetic behaviour, and the hysteresis loops increases with an increase in Mg content. The magnetisation increases as the Mg content is increased, which is might be related to the lower crystallite and particle sizes, as well as higher Fe 4+ /Fe 3+ ratio, as shown by X-ray diffraction and X-ray photoelectron spectroscopy, respectively. Analysis of the electrical properties showed grain–grain boundary effect in the conduction mechanism and two relaxation mechanisms for low Mg contents (x ≤ 0.2), whereas only the grain effect and one relaxation mechanism were observed at higher Mg contents (x = 0.3). The temperature dependence of direct current conductivity obeys the Arrhenius law. The activation energy for the conduction mechanism decreased with an increase in the Mg content. These results contribute the important knowledge in promising the candidate electrode material in electrochemical application.

Crosslinking-modulated direct-current conductivity of XLPE-PS composite via charge trap characteristics

Low direct-current (DC) conductivity is one of the most desired characteristics for crosslinked polyethylene (XLPE) as a high-voltage DC cable insulation material. In this Letter, a correlation between the DC conductivity and cross-linking characteristics of XLPE-polystyrene (PS) composites at 50 °C was studied. Experimental results show that by adjusting the cross-linking structure, different trap distribution characteristics for XLPE-PS composites were realized. With the increase in the cross-linking agent content, DC conductivities of XLPE-PS composites tend to decrease, and the introduced average trap depth increases correspondingly. An increase of 0.07 eV for average charge trap depth in XLPE-PS composites could be acquired in the test range. It is considered that the increase in the average trap depth reduces the carrier mobility, contributing to the reduction of DC conductivity for XLPE-PS composites. Thus, the DC conductivity and average trap depth of XLPE composites show a strong relevance. The results suggest that the interaction between PS particles and the matrix introduced by cross-linking plays a dominant role in determining the charge conduction for XLPE-PS composites.

Microwave absorption in epoxy composites filled with MoS2 and carbon nanotubes

In this study, the microwave absorbing properties of epoxy composites filled with micro-sized MoS2 and carbon nanotubes (CNT)/MoS2 were investigated in the frequency range of 1–67 GHz. Sample characterization was performed using electron microscopy and Raman spectroscopy methods. Direct current (DC) conductivity, complex permittivity, and shielding properties of composite materials with 50 wt. % of MoS2 and 1.5–2 wt. %CNT/50 wt.%MoS2 were measured. The permittivity of 50 wt. % MoS2/epoxy composite was found to be equal to 7.3, decreasing monotonically down to 4.5 at 67 GHz, while the imaginary part is equal to 1 and does not change. The addition of 2 wt. % of CNTs increases the real part of permittivity εr′ up to 30 at 1 GHz (13 at 67 GHz) and also leads to a large increase of the imaginary part of permittivity, with the most pronounced relaxation peak εr′′=10 at 10 GHz. Such an increase of dielectric loss correlates with the increase of DC conductivity up to 3.2 × 10−5 S/m as compared to the two-phase composite 50 wt. %MoS2/epoxy (σdc = 1.7 × 10−9 S/m). It was shown that 50 wt. %MoS2/epoxy composite exhibited an effective microwave absorption bandwidth of 9.9 GHz at the sample thickness of 2.0 mm with reflection loss minimum of -20.0 dB at 51.5 GHz. 2 wt. %CNT/50 wt. %MoS2/epoxy composite with a thickness of 0.9 mm showed a reflection loss minimum of −38 dB at 20.2 GHz with the absorption bandwidth of 3.68 GHz. The influence of sample thickness on position, width, and depth of EMR absorption maximums for the composites filled with MoS2 and mixed filler CNT/MoS2 was also determined.

Study of The Organic Solar Cells Based on An Emeraldine Salt of Conductive Polyaniline

Conductive polymer of Polyaniline is synthesized by doping with inorganic and organic acids, namely Hydrochloric acid (HCl) and Sulfuric acid (H2SO4). Thin film quality depended on the method of chemical polymerization. The electrical conductivity of these films was measured by two probe methods. The direct current (DC) conductivities (σDC) are found to be about 1.2×10-4 S/cm and 2.98×10-4 S/cm for PANI (HCl) and PANI (H2SO4), respectively. The electrical conductivity is influenced by preparation conduction such as concentration of the ionic salted acid HCl, H2SO4 and temperature. The best electrical conductivity about 2.98×10-4 S/cm was found at 383K. Conductive σDC is measured down to a temperature of ~100 K and the apparent change in the activation energies Ea are found to be 0.124 eV, and 0.112 eV for PANI-HCl, and H2SO4 doping respectively. Conductivity σDC is less temperature dependent near room temperature, further decrease in temperature the σDC is strongly dependent. In material characterization, successful doping is corroborated by FESEM study. PANI (H2SO4) exhibited highest conductivity followed by PANI (HCl). Polyaniline is one of imported polymers for solar cells.

Theoretical study on surface plasmon and hot carrier transport properties of Au(111) films

Metal films with a thickness as low as atomic layer have superior light absorption capabilities and conductive properties, especially the surface plasmons excited at the interface between metal film and dielectric can well capture photons and generate hot carriers, making them more efficient in improving the photoelectric conversion efficiency of solar cells, designing photodetectors in the near-infrared band, and sensors based on surface plasmon. However, there is still a lack of systematic theoretical studies on the surface plasmon and hot carrier properties of metal thin films. Based on the many-body first-principles calculation method, in this paper studied systematically are the surface plasmon properties of Au(111) films with thickness in a range from monolayer to 5 monolayers, and the energy distribution and transport properties of hot carriers generated by surface plasmons. The study results show that Au(111) films have low-loss surface plasmon properties. Meanwhile, the surface plasmons excited at the interface between the Au(111) film and the dielectric are strongly confined, which can enhance the local electric field, thus being crucial in nanophotonics applications. In addition, Au(111) film has a high efficiency generating hot carriers , and the generated hot electrons and hot holes are high in energy, and excellent in mean free path and mean free time. Unexpectedly, the direct current conductivity of Au(111) film is significantly better than that of bulk Au. These results provide new ideas and theoretical basis for the design and fabrication of Au(111) films in optoelectronic devices and energy conversion devices.

Maximum hopping direct current conductivity via hydrogen-like impurities in semiconductors

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 majority 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. Keywords: bulk crystals of germanium and silicon, hydrogen-like acceptors and donors, holes and electrons, band and hopping motion of charge carriers.