Large Charge Density Research Articles

Comprehensive contact analysis for vertical-contact-mode triboelectric nanogenerators with micro-/nano-textured surfaces

The triboelectric nanogenerator (TENG) is a new energy technology to convert mechanical energy into electricity based on contact charging and electrostatic induction. To increase the effective power generation in a limited device size, micro-/nano-textures are often designed at the contact surfaces. As the contact region decreases to micro/nano scale, adhesive forces such as van der Waals and electrostatic forces become dominant. However, there is currently no comprehensive model including micro-/nano-textures and the above adhesive forces, and thus the selection and design of textures are still lack of theoretical guidance. In this paper, the numerical contact and electrical models considering van der Waals and electrostatic forces are established, and the computational methods such as inexact Newton method, bi-conjugate stabilized (Bi-CGSTAB) method and fast Fourier transform (FFT) technique are employed to quantitatively analyze the effects of charge densities, applied loads, texture shapes and sizes on both contact and electrical performance. It is shown that the electrostatic force can be ignored when the charge density is small, while with large charge density, the electrical performance is significantly overestimated if the electrostatic forces are neglected. Among the four selected types of textures (pyramid, cone, cylinder and cube), the pyramid and cube textures are found to provide the larger output voltage under different applied loads, and also the optimal sizes for high voltage are presented, respectively. This study can provide the guideline for the texture design of high power generation TENGs.

Measuring the effective area and charge density of platinum electrodes for bionic devices

Objective. Neural stimulation is usually performed with fairly large platinum electrodes. Smaller electrodes increase the applied charge density, potentially damaging the electrode. Greater understanding of the charge injection mechanism is required for safe neural stimulation. Approach. The charge injection mechanism and charge injection capacity were measured by cyclic voltammetry. Electrodes were cleaned mechanically or by potential cycling in acidic solutions. The effective electrode area was measured by hydrogen adsorption or reduction of . Main results. The water window and safe potential window were affected by changes to electrolyte, electrode size, polishing method and oxygen concentration. Capacitance and Faradaic current contribute to the charge injection capacity. Varying voltammetric scan rate (measurement time), electrode size, polishing method, potential window, electrolyte and oxygen concentration affected the charge injection capacity and ratio of oxidation to reduction charge. Hydrogen adsorption in acidic solutions provided an inaccurate effective electrode area. Reduction of a solution phase redox species with a linear or radial diffusion profile could provide an effective electrode area. The charge density (charge injection capacity divided by electrode area) of a platinum electrode is dependent on the charge injection capacity and electrode area measurement technique. By varying cyclic voltammetric conditions, the charge density of platinum ranged from 0.15 to 5.57 mC cm−2. Significance. The safe potential window, charge injection mechanism, charge injection capacity and charge density of platinum depends on electrolyte, size of the electrode, oxygen concentration and differences in electrode polishing method. The oxidation and reduction charge injection capacities are not equal. Careful control of a platinum electrodes surface may allow larger charge densities and safe use of smaller electrodes. New electrode materials and geometries should be tested in a consistent manner to allow comparison of potential suitability for neural stimulation.

Leakage current conduction mechanisms and electrical properties of atomic-layer-deposited HfO2/Ga2O3 MOS capacitors

In this paper, current conduction mechanisms in HfO2/β-Ga2O3 metal–oxide–semiconductor (MOS) capacitors under positive and negative biases are investigated using the current–voltage (I–V) measurements conducted at temperatures from 298 K to 378 K. The Schottky emission is dominant under positively biased electric fields of 0.37–2.19 MV cm−1, and the extracted Schottky barrier height ranged from 0.88 eV to 0.91 eV at various temperatures. The Poole–Frenkel emission dominates under negatively biased fields of 1.92–4.83 MV cm−1, and the trap energy levels are from 0.71 eV to 0.77 eV at various temperatures. The conduction band offset (ΔEc) of HfO2/β-Ga2O3 is extracted to be 1.31 ± 0.05 eV via x-ray photoelectron spectroscopy, while a large negative sheet charge density of 1.04 × 1013 cm−2 is induced at the oxide layer and/or HfO2/β-Ga2O3 interface. A low C–V hysteresis of 0.76 V, low interface state density (Dit) close to 1 × 1012 eV−1 cm−2, and low leakage current density of 2.38 × 10−5 A cm−2 at a gate voltage of 7 V has been obtained, suggesting the great electrical properties of HfO2/β-Ga2O3 MOSCAP. According to the above analysis, ALD-HfO2 is an attractive candidate for high voltage β-Ga2O3 power devices.

Reverse electrodialysis in bilayer nanochannels: salinity gradient-driven power generation.

To evaluate the possibility of nano-fluidic reverse electrodialysis (RED) for salinity gradient energy harvesting, we consider the behavior of ion transportation in a bilayer cylindrical nanochannel consisting of different sized nanopores connecting two large reservoirs at different NaCl concentrations. Numerical simulations to illustrate the electrokinetic behavior at asymmetric sub-pore length and surface charge density are conducted, the impacts of which on transference number, osmotic current, diffusive voltage, maximum power and maximum power efficiency are systematically investigated. The results reveal that the transference number in Config. I (where high NaCl concentration is applied at the larger nanopore) is always larger than that in the opposite configuration (Config. II). At low concentration ratios, the osmotic current and maximum power have maximum values, while the maximum power efficiency decreases consistently. For Config. II, the ion transportation is impacted by the surface charge density at both sub-nanopores, while for Config. I, it is determined by the surface charge density at the downstream small nanopore. When large surface charge density is applied at the downstream small nanopore in contact with a very low concentration reservoir, there exists an interesting phenomenon: the larger surface charge density at the large nanopore induces a slight performance drop due to the impact of upstream EDL overlap.

Arbitrarily Large Solutions of the Vlasov--Poisson System

We study smooth, global-in-time solutions of the Vlasov--Poisson system in the plasma physical case that possess arbitrarily large charge densities and electric fields. In particular, we construct two classes of solutions with this property. The first class consists of spherically symmetric solutions that initially possess arbitrarily small density and field values but attain arbitrarily large values of these quantities at some later time. Additionally, we construct a second class of spherically symmetric solutions that possess any desired mass and attain arbitrarily large density and field values at any later prescribed time.

Porous Fe2O3 microcubes derived from metal organic frameworks for efficient elimination of organic pollutants and heavy metal ions

Increasing specific surface area and functional groups are two key ways to improve the adsorption performance of adsorbent materials. Herein, porous Fe2O3 (P-Fe2O3) microcubes composed of fine Fe2O3 nanoparticles (NPs) were facilely synthesized through the simultaneous oxidative decomposition of Prussian blue (PB) microcubes. Owing to their integrated features (i.e., large specific surface area of ∼155 m2 g−1 and large amount of Fe2O3 NPs), the synthesized P-Fe2O3 exhibited excellent adsorption capacities for heavy metal ions (175.5 mg g−1 for Cr(VI) and 97.8 mg g−1 for Pb(II)) and organic contaminants (159.4 mg g−1 for humic acid and 425.9 mg g−1 for methyl blue) from aqueous solutions. Based on the batch experiments, the adsorption isotherms could significantly conform to the Langmuir models. Combined with the microscopic analysis, the results suggested that the enrichment of Pb(II) on P-Fe2O3 was mainly attributed to the chemical binding between the electron donating oxygen ions of P-Fe2O3 surface and Pb(II), while the large available positive charge density could facilitate the effective adsorption of Cr(VI) due to ion exchange and electrostatic attraction. Furthermore, the surface complexation of organic pollutants on P-Fe2O3 was depended on the dipole moment and molar volume of the organic pollutant molecules. The consequences indicated that P-Fe2O3 could be served as a promising material for the decontamination of organic contaminants as well as the elimination of heavy metal ions from aqueous solutions. The findings presented herein played important roles in the purification of inorganic and organic contaminants on the available of inexpensive P-Fe2O3 NPs in natural environmental pollution cleanup applications.

Note: A self-calibrating wide range electrometer for in-cloud measurements.

Charge is observed in clouds of all forms, which may influence their development and properties. In-cloud charge measurements require a wide dynamic range, extending from charge in aerosols and dusts to that present in thunderstorms. Unexpectedly large charge densities (>200 pC m-3) have recently been detected in layer clouds using balloon-carried linear electrometers. These, however, lead to instrument saturation if sufficient sensitivity for aerosol and droplet charge is maintained. Logarithmic electrometers provide an alternative but suffer strong non-linear thermal effects. This is a limitation for balloon-carried instruments that encounter temperature changes up to ∼100 °C, as full thermal compensation requires complexity inappropriate for disposable devices. Here, a novel hybrid system is described, combining linear and logarithmic electrometers to provide extended dynamic range (±50 pA), employing the negligible (±4%) total temperature drift of the linear device to provide in situ calibration of the logarithmic device. This combination opens up new measurement opportunities for charge in clouds, dusts, and aerosols.

Holographic heavy baryons in the Witten-Sakai-Sugimoto model with the D0-D4 background

We extend the holographic analysis of the light-baryon spectrum by Cai et al. [Phys. Rev. D 90, 106001 (2014)] to the case involving the heavy flavors. With the construction of the Witten-Sakai-Sugimoto model in the D0-D4 background, we use the mechanism proposed by Liu and Zahed by including two light-flavor and one heavy-flavor brane, to describe the heavy-light baryons as heavy mesons bound to a flavor instanton. The background geometry of this model corresponds to an excited state in the dual field theory with a nonzero glue condensate $⟨\mathrm{Tr}\mathcal{F}\ensuremath{\wedge}\mathcal{F}⟩=8{\ensuremath{\pi}}^{2}{N}_{c}\stackrel{\texttildelow{}}{\ensuremath{\kappa}}$ (or equivalently a nonzero $\ensuremath{\theta}$ angle), which is proportional to the number density of the D0-brane charge. In the strong-coupling limit, this model shows that the heavy meson is always bound in the form of the zero mode of the flavor instanton in the fundamental representation. We systematically study the quantization of the effective Lagrangian of heavy-light baryons by employing the soliton picture, and derive the mass spectrum of heavy-light baryons in the situation with single- and double-heavy baryons. We find that the difference in the mass spectrum becomes smaller if the density of the D0-brane charge increases, and the stability constraint of the heavy-light baryons is $1<b<3$. This indicates that a baryon cannot stably exist for a sufficiently large D0 charge density, which is in agreement with the conclusions in the previous study of this model.

Electrochemical investigation of electrochromic device based on WO3 and Ti doped V2O5 films by using electrolyte containing ferrocene

Electrochromic devices (ECDs) based on WO3 and Ti doped V2O5 films are fabricated by using lithium (LiClO4) liquid electrolyte containing ferrocene redox couple. The addition of ferrocene in electrolyte enhances electrochromic properties of device. The device based on LiClO4-Ferrocene electrolyte has larger charge density than that based on LiClO4 electrolyte. In the 600–1500nm wavelength range, the transmittance of colored device is under 2% and it has faster coloring response. At 680nm wavelength, it shows larger changes in transmittance from 68% to 1.8% while device based on LiClO4 electrolyte changes transmittance from 68.3% to 11.5%. The cycling data reveal that device based on LiClO4-Ferrocene electrolyte can yield more stable electrochromic properties at 65°C than room temperature. In order to deeper understand the effect of electrolyte on films and devices, electrochemical impedance spectroscopy (EIS) and the voltage distribution of films based on an analog cell are separately measured and analyzed in LiClO4 and LiClO4-Ferrocene electrolytes. Results indicate that compared with LiClO4 electrolyte, films have lower charge-transfer resistance and the distributed voltage on Ti doped V2O5 film is larger in LiClO4-Ferrocene electrolyte, which can enhance optical properties of ECD by improving charge density of Ti doped V2O5 film.

Holographic entanglement entropy of a 1 + 1 dimensional p-wave superconductor

We examine the behavior of entanglement entropy SAEE of a subsystem A in a fully backreacted holographic model of a 1 + 1 dimensional p wave superconductor across the phase transition. For a given temperature, the system goes to a superconducting phase beyond a critical value of the charge density. The entanglement entropy, considered as a function of the charge density at a given temperature, has a cusp at the critical point. In addition, we find that there are three different behaviors in the condensed phase, depending on the subsystem size. For a subsystem size l smaller than a critical size lc1, SAEE continues to increase as a function of the charge density as we cross the phase transition. When l lies between lc1 and another critical size lc2 the entanglement entropy displays a non-monotonic behavior, while for l > lc2 it decreases monotonically. At large charge densities SAEE appears to saturate. The non-monotonic behavior leads to a novel phase diagram for this system.

Direct C2-arylation of quinoline N-oxides by boronic esters; a molecular approach on the efficient metal-free method in C–C cross-coupling reactions

Kinetic and thermodynamic aspects of the cross-coupling reaction of quinoline N-oxides by various boronic esters in the gas and solvent phases were investigated, theoretically. Two types of boronic esters were considered for the reaction. There are various substitutes in types 1 and 2 which bonded to oxygen and boron atoms, respectively. For investigation of the chemical kinetic aspects of both types, different characters of the rate-determining step (RDS) were considered. Electron density of the involved bonds at the TS, natural charge density of the atoms and donor–accepter orbital interactions are the criteria which were used for the RDS justification of type 1. Nucleus-independent chemical shifts index was applied for description of type 2 behavior in cross-coupling reactions. Theoretical evaluation reveals that a large charge density on the oxygen atom of the O–B bond leads to a higher ability of proton abstraction which reduces ∆G ≠ values in type 1 boronic esters. Furthermore, a large aromaticity character in the quinoline ring at the TS in type 2 boronic esters causes a decrease in the ∆G ≠ value. Finally, based on the obtained results, the ability of proton abstraction of type 1 and the aromaticity character of type 2 boronic esters are the main factors in the energy barrier of the studied reactions.

Hydrodynamic model of a dielectric-barrier discharge in pure chlorine

A one-dimensional hydrodynamic model of a dielectric-barrier discharge (DBD) in pure chlorine is developed, and the properties of the discharge are modeled. The discharge is excited in an 8-mm-long discharge gap between 2-mm-thick dielectric quartz layers covering metal electrodes. The DBD spatiotemporal characteristics at gas pressures of 15–100 Torr are modeled for the case in which a 100-kHz harmonic voltage with an amplitude of 8 kV is applied to the electrodes. The average power density deposited in the discharge over one voltage period is 2.5–5.8 W/cm3. It is shown that ions and electrons absorb about 95 and 5% of the discharge power, respectively. In this case, from 67 to 97% of the power absorbed by electrons is spent on the dissociation and ionization of Cl2 molecules. Two phases can be distinguished in the discharge dynamics: the active (multispike) phase, which follows the breakdown of the discharge gap, and the passive phase. The active phase is characterized by the presence of multiple current spikes, a relatively high current, small surface charge density on the dielectrics, and large voltage drop across the discharge gap. The passive phase (with no current spikes) is characterized by a low current, large surface charge density on the dielectrics, and small voltage drop across the discharge gap. The peak current density in the spikes at all pressures is about 4 mA/cm2. In the multispike phase, there are distinct space charge sheaths with thicknesses of 1.5–1.8 mm and a mean electron energy of 4.3–7 eV and the central region of quasineutral plasma with a weak electric field and a mean electron energy of 0.8–3 eV. The degree of ionization of chlorine molecules in the discharge is ~0.02% at a pressure of 15 Torr and ~0.01% at 100 Torr. The DBD plasma is electronegative due to the fast attachment of electrons to chlorine atoms: e + Cl2 → Cl + Cl–. The most abundant charged particles are Cl 2 + and Cl− ions, and the degree of ionization during current spikes in the active phase is (4.1–5.5) × 10–7. The mechanism of discharge sustainment is analyzed. The appearance of a series of current spikes in the active phase of the discharge is explained.

2D Frameworks of C2 N and C3 N as New Anode Materials for Lithium-Ion Batteries.

Novel layered 2D frameworks (C3 N and C2 N-450) with well-defined crystal structures are explored for use as anode materials in lithium-ion batteries (LIBs) for the first time. As anode materials for LIBs, C3 N and C2 N-450 exhibit unusual electrochemical characteristics. For example, C2 N-450 (and C3 N) display high reversible capacities of 933.2 (383.3) and 40.1 (179.5) mAh g-1 at 0.1 and 10 C, respectively. Furthermore, C3 N shows a low hypothetical voltage (≈0.15 V), efficient operating voltage window with ≈85% of full discharge capacity secured at >0.45 V, and excellent cycling stability for more than 500 cycles. The excellent electrochemical performance (especially of C3 N) can be attributed to their inherent 2D polyaniline frameworks, which provide large net positive charge densities, excellent structural stability, and enhanced electronic/ionic conductivity. Stable solid state interface films also form on the surfaces of the 2D materials during the charge/discharge process. These 2D materials with promising electrochemical performance should provide insights to guide the design and development of their analogues for future energy applications.

Magnetic Porous Carbonaceous Material Produced from Tea Waste for Efficient Removal of As(V), Cr(VI), Humic Acid, and Dyes

Magnetic porous carbonaceous (MPC) materials derived from tea waste were synthesized by an integrated biosorption–pyrolysis process and were applied as adsorbents for wastewater cleanup. On the basis of various characterizations, we demonstrated that the formation mechanism of γ-Fe2O3 anchored on the porous carbonaceous material surface consisted of the adsorption of iron ions and then the γ-Fe2O3 nucleation and growth through pyrolysis at alternative peak temperatures (300–500 °C). The sample pyrolyzed at 300 °C (MPC-300) showed good capacities for As(V) (38.03 mg g–1) and Cr(VI) (21.23 mg g–1) adsorption, outperforming that of commercial bulk Fe2O3 and many other materials. Moreover, the large available positive charge density can facilitate the effective adsorption of anionic dye (MO) and humic acid (HA) on the γ-Fe2O3 surface while the adsorption performance is sluggish for cationic dyes (MB and RhB). Relatively, the adsorption isotherms could significantly conform to the Langmuir model, and the pseud...

TSDC and impedance spectroscopy measurements on hydroxyapatite, β-tricalcium phosphate and hydroxyapatite/β-tricalcium phosphate biphasic bioceramics

Bone grafting and surgical interventions related with orthopaedic disorders consist in a big business, generating large revenues worldwide every year. There is a need to replace the biomaterials that currently still dominate this market, i.e., autografts and allografts, due to their disadvantages, such as limited availability, need for additional surgeries and diseases transmission possibilities. The most promising replacement materials are biomaterials with bioactive properties, such as the calcium phosphate-based bioceramics group. The bioactivity of these materials, i.e., the rate at which they promote the growth and directly bond with the new host biological bone, can be enhanced through their electrical polarization.In the present work, the electrical polarization features of pure hydroxyapatite (Hap), pure β-tricalcium phosphate (β-TCP) and biphasic hydroxyapatite/β-tricalcium phosphate composites (HTCP) were analyzed by measuring thermally stimulated depolarization currents (TSDC). The samples were thermoelectrically polarized at 500°C under a DC electric field with a magnitude of 5kV/cm. The biphasic samples were also polarized under electric fields with different magnitudes: 2, 3, 4 and 5kV/cm. Additionally, the depolarization processes detected in the TSDC measurements were correlated with dielectric relaxation processes observed in impedance spectroscopy (IS) measurements.The results indicate that the β-TCP crystalline phase has a considerable higher ability to store electrical charge compared with the Hap phase. This indicates that it has a suitable composition and structure for ionic conduction and establishment of a large electric charge density, providing great potential for orthopaedic applications.

Cartilage-like electrostatic stiffening of responsive cryogel scaffolds

Cartilage is a structural tissue with unique mechanical properties deriving from its electrically-charged porous structure. Traditional three-dimensional environments for the culture of cells fail to display the complex physical response displayed by the natural tissue. In this work, the reproduction of the charged environment found in cartilage is achieved using polyelectrolyte hydrogels based on polyvinyl alcohol and polyacrylic acid. The mechanical response and morphology of microporous physically-crosslinked cryogels are compared to those of heat-treated chemical gels made from the same polymers, as a result of pH-dependent swelling. In contrast to the heat-treated chemically-crosslinked gels, the elastic modulus of the physical cryogels was found to increase with charge activation and swelling, explained by the occurrence of electrostatic stiffening of the polymer chains at large charge densities. At the same time, the permeability of both materials to fluid flow was impaired by the presence of electric charges. This cartilage-like mechanical behavior displayed by responsive cryogels can be reproduced in other polyelectrolyte hydrogel systems to fabricate biomimetic cellular scaffolds for the repair of the tissue.

Some aspects of dimensionality and phase transitions of organic–inorganic hybrid perovskite (n-C14H29NH3)2ZnCl4

The differential scanning calorimetery and the differential thermal analysis thermograms were performed over a suitable wide range of temperatures on polycrystalline samples of the titled hybrid. Furthermore, the ac conductivity σ ac(ῳ,T) and the complex dielectric permittivity e *(ῳ,T) as function of temperature 120 K < T < 400 K and some selected frequencies in the range 1 kHz ≤ f ≤ 100 kHz were measured and presented. The combination of the measured parameters confirms, without any doubt, the existence of a first-order reversible solid–solid structural phase transition from intercalation to non-intercalation, at T ≈ 368 K accompanied by a sudden increase of the interlayer spacing by ≈17.5%. The analysis of our data is based on the coordination complex and the dimensionality of the central metal halide arrangements, which, in our case, is isolated square [ZnCl4]−2 tetrahedral coordination and, hence, of zero-dimensionality (0D), but stabilized in a two-dimensional structure through charge-assisted hydrogen-bonding system. The zero-dimensionality results in a large charge density and, hence, of high efficiently packed compared with other hybrids of this series which are usually crystallized in two-dimensional (2D) corner-sharing [MCl6]−2. The rule of hydrogen bonding has been considered. The odd–even effects were given.

High performance thin film transistor (flex-TFT) with textured nanostructure ZnO film channel fabricated by exploiting electric double layer gate insulator

We report a flexible thin film transistor (flex-TFT) fabricated on a commonly available polyimide (Kapton®) tape with a channel of highly textured nanocrystalline ZnO film grown by pulsed laser deposition. The flex-TFT with an electric double layer (EDL) gate insulator shows a low threshold for operation (Vth ≤ 1 V), an ON/OFF ratio reaching ≈107 and a subthreshold swing ≈75 mV/dec. The superior performance is enabled by a high saturation mobility (μs ≈ 70 cm2/V s) of the highly textured nanocrystalline channel. The low Vth arises from large charge density (≈1014/cm2) induced into the channel by EDL gate insulator. The large charge density induced by the EDL gate dielectric also enhances the Hall mobility in the film and brings down the sheet resistance by nearly 2 orders, which leads to large ON/OFF ratio. The flex-TFT operation can be sustained with reproducibility when the TFT is bent down to a radius of curvature ≈2 cm.

Signal deformation at high ion concentration in atmospheric pressure laser ionization ion mobility spectrometry (APLI-IMS)

When using laser radiation for ionization in ion mobility spectrometry, a large increase in the number of produced ions compared to e.g. standard radioactive sources can be achieved. This number can be so large that Coulomb broadening of the measured mobility signal can be observed. From a large enough charge density on, the Coulomb repulsion leads to effects on the motion of the ions that manifest themselves in deformations of the signal in addition to the broadening. Here we have investigated with help of finite elements method simulations the cause of this deformation and compared the calculated signals with measured ones. An important result is that the change of electric field strength when entering the drift region and its effect on the ion cloud distribution is a main factor responsible for the signal deformation.

Oxygen-Molecule Adsorption and Dissociation on BCN Graphene: A First-Principles Study.

Boron and nitrogen co-doped (BCN) graphene is an attractive material for use as a metal-free oxygen reduction reaction electrocatalyst and as other catalysts due to its unique structure and electronic properties. Reported here is the structure, determined by using density functional theory, of the active O2 -dissociation site of BCN graphene containing different types of BN cluster. The results show that the edge termination and shape of substitutional BN clusters are two important factors that determine the catalytic activity of BCN graphene for the dissociation of molecular oxygen. N-Terminated triangular BN (t-BN) cluster doping can reduce the energy barrier more effectively compared to a t-BN with a B edge or quadrangular BN cluster. Interestingly, the B atom neighboring the N edge, only in the case of N-terminated t-BN doping, is determined to be the most active site for O2 dissociation due to the barrier being as low as 0.08 eV. The electronic structure calculations reveal that in addition to the large positive charge densities, the catalytic activity of graphene enhanced by B,N doping is also attributed to the increased density of states of the π* states of the active site around the Fermi level.