Dc Bias Potential Research Articles

Deciphering Highly Sensitive Non-Enzymatic Glucose Sensor Based on Nanoscale CuO/PEDOT-MoS2 Electrodes in Chronoamperometry

The present work demonstrates fabrication of a non-enzymatic glucose sensor based on CuO nanoparticles deposited over poly(3,4-ethylenedioxythiophene) (PEDOT) conducting polymer infiltrated with nanoscale MoS2. Structural, morphological and elemental analyses of the fabricated sensor electrodes were performed via different characterization techniques like X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), elemental dispersive X-ray spectroscopy (EDX), and Fourier transform infra-red spectroscopy (FT-IR). The cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) studies of the hybrid nanoelectrode (CuO/PEDOT-MoS2) exhibited better redox activity and electron transfer kinetics, as compared with the CuO/PEDOT and CuO only systems. Accordingly, the electrochemical parameters of all the systems were determined and compared at large. The CuO/PEDOT-MoS2 hybrid electrode system offered a significant enhancement in the electroactive area (∼1.47 cm2) and rate constant (0.76 s−1) upon oxidizing glucose into gluconic acid. In the CV responses, an augmented activity was monitored at +0.6 V which was considered as the dc bias potential in the chronoamperometric experiment for detecting glucose suitably. The sensor electrode yielded a low LOD of 0.046 μM and with a sensitivity magnitude as high as 829 μA mM−1 cm−2 over a wide linear range, between 30 μM to 1.06 mM of glucose concentration. Deployment of organic-inorganic nanomaterial based non-enzymatic sensor would find immense scope in non-clinical diagnostics and pharmaceutical applications for fast, convenient and smart sensing.

Monolithic In‐Plane Integration of Gate‐Modulated Switchable Supercapacitors

Monolithic integration of iontronic devices is a key challenge for future miniaturization and system integration. The G‐Cap, a novel iontronic element, is a switchable supercapacitor with gating characteristics comparable to transistors in electronic circuits, but switching relies on ionic currents and ion electroadsorption. The first monolithic in‐plane G‐Cap integration through 3D‐inkjet printing of nanoporous carbon precursors is reported. The printed G‐Cap has a three‐electrode architecture integrating a symmetric “working” supercapacitor (W‐Cap) and a third “gate” electrode (G‐electrode) that reversibly depletes/injects electrolyte ions into the system, effectively controlling the “working” capacitance. The symmetric W‐Cap operates with a proton‐conducting hydrogel electrolyte PVA/H2SO4 and shows a high capacitance (1.6 mF cm−2) that can be switched “on” and “off” by applying a DC bias potential (−1.0 V) at the G‐electrode. This effectively suppresses AC electroadsorption in the nanoporous carbon electrodes of the W‐Cap, resulting in a high capacitance drop from an “on” to an “off” state. The new monolithic structures achieve high rate performance, reversible on‐off switching with an off‐value reaching 0.5 %, which even surpasses recently reported values. Establishing technologies and device architectures for functional ionic electroadsorption devices is crucial for diverse fields ranging from microelectronics and iontronics to biointerfacing and neuromodulation.

A Comprehensive Examination of Voltammetric Parameters in Fourier Transform Sine‐wave Voltammetry (FT‐SWV) Leading to Concentration Linearity and High Signal‐to‐background Ratio

AbstractThere has not been a comprehensive investigation of the effect of voltammetric parameters: amplitude, dc bias potential, and excitation frequency of the sine waveform in Fourier Transform Sine‐Wave Voltammtery (FT‐SWV) on background, signal, and signal‐to‐background ratio as well as linearity with respect to the concentration of an analyte. FT‐SWV of ruthenium hexamine (III) chloride (RuHex) demonstrates that the dc bias potential can be used to adjust the phase angle difference between the signal and background to obtain out‐of‐phase background. Several conditions show a high signal‐to‐noise ratio and good concentration linearity. The lessons from RuHex guided us to conditions for good signal‐to‐background ratio and concentration linearity for dopamine (DA).

Switchable Supercapacitors with Transistor‐Like Gating Characteristics (G‐Cap)

AbstractA novel three‐electrode electrolyte supercapacitor (electric double‐layer capacitor [EDLC]) architecture in which a symmetrical interdigital “working” two‐electrode micro‐supercapacitor array (W‐Cap) is paired with a third “gate” electrode that reversibly depletes/injects electrolyte ions into the system controlling the “working” capacity effectively is described. All three electrodes are based on precursor‐derived nanoporous carbons with well‐defined specific surface area (735 m2 g−1). The interdigitated architecture of the W‐Cap is precisely manufactured using 3D printing. The W‐Cap operating with a proton conducting PVA/H2SO4‐hydrogel electrolyte and high capacitance (6.9 mF cm−2) can be repeatedly switched “on” and “off”. By applying a low DC bias potential (−0.5 V) at the gate electrode, the AC electroadsorption in the coupled interdigital nanoporous carbon electrodes of the W‐Cap is effectively suppressed leading to a stark capacity drop by two orders of magnitude from an “on” to an “off” state. The switchable micro‐supercapacitor is the first of its kind. This general concept is suitable for implementing a broad range of nanoporous materials and advanced electrolytes expanding its functions and applications in future. The integration of intelligent functions into EDLC devices has extensive implications for diverse areas such as capacitive energy management, microelectronics, iontronics, and neuromodulation.

Reactive HiPIMS deposition of Ti-Al-N: Influence of the deposition parameters on the cubic to hexagonal phase transition

Reactive high-power impulse magnetron sputtering (R-HiPIMS) is seen as a key-technology for the deposition of future hard and multifunctional coatings. Increased ionisation rates allow for additional possibilities in tuning specific coating characteristics based on growth mechanisms varied by surface-diffusion. Especially within the well-established Ti-Al-N system, the Al solubility limit (xmax) of metastable face-centred-cubic (fcc) Ti1−xAlxN is an everlasting scientific topic. Here, we investigate in detail the dependence of xmax on various deposition parameters (i.e. pulse frequency and duration, N2-to-Ar flow rate ratio, and substrate bias potential) during R-HiPIMS of Ti-Al-N coatings using Ti0.6Al0.4, Ti0.5Al0.5 and Ti0.4Al0.6 composite targets. The systematic studies showed that the highest solubility limit of xmax ∼0.55 could be obtained for duty cycles around 3.75 % (peak power densities of ∼1.0 kW/cm2) and a N2-to-Ar flow rate ratio of 0.3. A further decisive fact for the deposition of high Al containing fcc-structured Ti1−xAlxN coatings is surface diffusion controlled by bias potentials (DC as well as modulated pulses) ensuring sufficient intermixing of the arriving film species. Despite the presence of very small amounts of wurtzite-typed phases, excellent hardness values of ∼36 GPa for Ti0.40Al0.60N – which further increased to ∼40 GPa upon annealing for 1 h at 700 °C – could be achieved for a DC bias potential of -50 V, irrespective of all variations conducted. Based on our results we can further conclude, that the ratio and energy of Tin+- and Aln+-ions, simultaneously arriving at the substrate surface, are decisive for stabilising the highly preferred cubic modification. A distinct promotion of specific discharge regimes – selected by synchronised bias pulses – can thus positively influence the cubic phase formation through altered gas-to-metal ion ratios arriving at the film surface.

Third generation impedimetric sensor employing direct electron transfer type glucose dehydrogenase

Faradaic electrochemical impedance spectroscopy (faradaic EIS) is an attractive measurement principle for biosensors. However, there have been no reports on sensors employing direct electron transfer (DET)-type redox enzymes based on faradaic EIS principle. In this study, we have attempted to construct the 3rd-generation faradaic enzyme EIS sensor, which used DET-type flavin adenine dinucleotide (FAD) dependent glucose dehydrogenase (GDH) complex, to elucidate its characteristic properties as well as to investigate its potential application as the future immunosensor platform. The gold disk electrodes (GDEs) with DET-type FADGDH prepared using self-assembled monolayer (SAM) showed the glucose concentration dependent impedance change, which was confirmed by the change in the charge transfer resistance (Rct). The Δ(1/Rct) values were also affected by DC bias potential and the length of SAM. Based on the Nyquist plot and Bode plot simulations, glucose sensing by imaginary impedance monitoring under fixed frequency (5 mHz) was carried out, revealing the higher sensitivity at low glucose concentration with wider linear range (0.02–0.2 mM). Considering this high sensitivity toward glucose, the 3rd-generation faradaic enzyme EIS sensor would provide alternative platform for future impedimetric immunosensing system, which does not use redox probe.

Electrical Properties of Cerium and Yttrium Co-substituted Strontium Nanohexaferrites

Ce and Y substituted SrFe12O19 (x = 0.4 and 0.5) nanohexaferrites have been synthesised by sol–gel auto-combustion. The pure hexagonal SrFe12O19 phase was confirmed by XRD, FE-SEM and HR-TEM. The ac conductivity and dielectric properties of Ce and Y substituted Sr:Fe12O19 nanohexaferrites were studied by using complex impedance technique. Dielectric properties such as dielectric constant, dielectric loss, dielectric tangent loss, as well as ac conductivity are measured at various bias potentials in a varying frequency range from 10 Hz to 10 MHz. The frequency dependency of the ac conductivity could be evaluated by a power exponent law at higher frequencies, which is a characteristic mechanism for electrical charge transport by tunnelling processes with which it is more dispersive at lower frequencies. The conduction mechanisms were also investigated at various dc bias potentials, mainly being an indicative of hopping type conduction. So, the dielectric dispersion behaviour can be well elucidated in terms of Maxwell–Wagner polarization in accordance with the Koop’s phenomenological theory. Utilizing an electrical equivalent circuit model, impedance studies were carried out in a specific frequency domain to characterize all the contributions of the dielectric response between the grains and grain boundaries to the dielectric parameters.

Calculation of the radial electric field with RF sheath boundary conditions in divertor geometry

The equilibrium electric field that results from an imposed DC bias potential, such as that driven by a radio frequency (RF) sheath, is calculated using a new minimal two-field model in the BOUT++ framework. Biasing, using an RF-modified sheath boundary condition, is applied to an axisymmetric limiter, and a thermal sheath boundary is applied to the divertor plates. The penetration of the bias potential into the plasma is studied with a minimal self-consistent model that includes the physics of vorticity (charge balance), ion polarization currents, force balance with , ion diamagnetic flow (ion pressure gradient) and parallel electron charge loss to the thermal and biased sheaths. It is found that a positive radial electric field forms in the scrape-off layer and it smoothly connects across the separatrix to the force-balanced radial electric field in the closed flux surface region. The results are in qualitative agreement with the experiments. Plasma convection related to the net flow in front of the limiter is also obtained from the calculation.

Cerium doping of Ti-Al-N coatings for excellent thermal stability and oxidation resistance

Ti–Al–N thin films are well established due to their outstanding thermo-mechanical properties. Nevertheless, this system is still a subject of many research activities to further enhance their oxidation resistance and thermal stability. The addition of reactive elements, such as Cerium, can significantly improve especially the oxidation resistance of various materials. Therefore, we study in detail the impact of Ce (2 at.% alloyed to powder metallurgically prepared Ti0.50Al0.50 targets) on growth processes, structure, mechanical properties, thermal stability, and oxidation resistance of magnetron sputtered Ti1−x−yAlxCeyN coatings prepared with DC bias potentials of Ubias=−25, −50, −75, and −100V. The deposition rate is significantly increased by a factor of ~1.75 (Ubias=−25V) to 1.45 (Ubias=−100V) when using Ti0.49Al0.49Ce0.02 instead of Ti0.50Al0.50 targets. Furthermore, also the hardness of the resulting single phase face centered cubic Ti0.43Al0.55Ce0.02N is with ~35GPa above that of Ti0.42Al0.58N with ~34GPa, for coatings on polycrystalline Al2O3 and Ubias=−50V.All temperature dependent characteristics of Ti0.42Al0.58N are improved significantly by the addition of Cerium. Wurtzite-structured AlN formation within Ti0.43Al0.55Ce0.02N can only be detected at Ta=1100°C, about 200°C higher as for Ti0.42Al0.58N. Their peak-hardness, due to spinodal decomposition of the supersaturated cubic phase is ~37.0GPa with Ta=900°C, as compared to 34.6GPa with Ta=800°C for Ti0.42Al0.58N. Additionally, even after exposure to ambient air at 950°C for 3h, still >50% of the Ti0.43Al0.55Ce0.02N coating is intact (below the ~1.2μm thin oxide scale), whereas Ti0.42Al0.58N is already fully oxidized.Based on our results we can conclude, that Ce-doping improves the deposition characteristics and mechanical properties as well as thermal stabilities (incl. oxidation resistance) of Ti–Al–N, to be used as protective coatings for a wide range of high-demanding applications.

Impact of helium ion energy modulation on tungsten surface morphology and nano-tendril growth

Time-modulated helium (He) ion energy (e.g. VBias = −50 + 25·sin(2πfRF · t), fRF = 13.56 MHz) is demonstrated to strongly affect the development of tungsten (W) surface morphology that results from He plasma irradiation in the DIONISOS linear plasma experiment. Nano-tendril bundles (NTBs), which appear as isolated ‘islands’ of nano-tendrils, can rapidly grow on an otherwise smooth W surface. This is in contrast to previously seen full-surface coverage of nano-tendril growth known as ‘fuzz’. When tall NTBs form, less than 15% of the surface contains nano-tendrils. The NTB surface coverage changes with growth conditions and the total volume of nano-tendrils in the NTBs is observed to be up to a factor of 16 larger than when fuzz is grown. This indicates that long-range W surface transport underlies nano-tendril formation.Surface temperature 870–1220 K, the DC bias potential −30 to −70 V, and the ion flux density 4.4 × 1021–1.1 × 1022 He · m−2 · s−1 are varied in the experiments. NTBs form at similar conditions as fuzz with the critical difference being the RF modulation of the ion energy bombarding the W, another indication of the importance of W surface transport. Mass loss measurements indicate net erosion with a yield of 1–8 × 10−4 W/He when NTBs form; erosion that is not attributable to chemical or physical sputtering by He or impurities in the plasma. The erosion is correlated to the NTB growth, based on post-exposure inspection by electron microscopy indicating that NTBs are prone to loss from the surface. NTB growth is compared to the empirical growth-erosion model of fuzz, showing NTBs grow up to a factor of 100 times taller than the expected fuzz layer depth under DC bias conditions. Insights into nano-tendril growth provided by this new growth regime are discussed. Strategies to mitigate W fuzz growth may inadvertently result in rapid localized nano-tendril bundle growth with a higher probability of dust production.

Anodization of titanium in radio frequency oxygen discharge — Microstructure, kinetics & transport mechanism

Plasma anodization in oxygen discharges is a prominent technique in semiconductor processing, allowing nearly defect-free oxidation at low temperatures. Here we apply inductively coupled radio frequency oxygen plasma anodization to titanium and study the effect of temperature and dc bias potential on the oxide film morphology. To achieve a detailed understanding of the growth process, the oxide crystal phase is characterized by Raman spectroscopy and the orientation between the oxide film and the substrate is determined by TEM. The constant voltage oxidation kinetics is modelled and growth experiments with inert markers allow to identify the ionic species controlling the growth rate. Plasma anodization experiments in combination with SIMS depth profiling of the interface region add to these experiments and prove that oxygen is the mobile species in the titania layer. The applied kinetic model allowed the determination of the activation energy for ionic transport with values of 1.31eV at 200°C and 1.58eV at 400°C and 550°C. As oxygen ion transport is likely responsible for film growth, the observed surface morphologies were most likely formed by oxygen ion sputtering or result from initial nucleation processes.

Ce0.6Mn0.3Fe0.1O2-δ as an Alternative Cathode Material for High Temperature Steam Electrolysis Using LaGaO3-based Oxide Electrolyte

Ce0.6Mn0.3Fe0.1O2-δ (CMF) has been used as a new oxide cathode of solid oxide electrolysis cell (SOEC) using LaGaO3-based electrolyte for H2 production under a feeding gas composition of 20%steam/1%H2/79%Ar. CMF cathode exhibits good electrolysis performance and well-performed hydrogen production rate with the Faraday’s law at 1173-973K. Through impedance measurement under a DC polarized condition, the studies show that polarization resistance and ohmic resistance decreased with increasing DC bias potential. Furthermore, CMF showed good stability, and no significant aggregation and delamination were noticed during the electrolysis measurement. These results suggest that CMF can be a promising oxide cathode candidate for intermediate temperature SOEC.

Electrical performance of soft polymer ionic membranes with mono and multi polymer systems

We prepared the Polyvinyl alcohol (PVA)/CdCl2 and PVA/Polyvinylpyrrolidone (PVP)/CdCl2 composites by solution blending known as the soft polymer ionic membrane (SPIM). The loading of CdCl2 divalent ions demonstrates an influence over the electronic structure was confirmed by UV analysis. The bright divalent ionic morphology observed by scanning electron microscopy (SEM). The optimization of specific capacitance (Cp) and the dielectric constant disclosed as a function of an external DC bias potential. The trend of polarization was inversely proportional to the DC bias with the PVA system and directly to the PVP system. We disclosed the dielectric constant as a function of ionic loading. The optimized dielectric constant for various applications.

Oxygen Nonstoichiometry and Cathodic Property of Ce0.6Mn0.3Fe0.1O2-δ for High Temperature Steam Electrolysis Cell Using LaGaO3-Based Oxide Electrolyte

Steam electrolysis was studied by using a new oxide cathode of Ce0.6Mn0.3Fe0.1O2- d (CMF). It found that this cathode showed almost same performance compared with a conventional Ni-based cathode without H2 flow and H2 generation rate obeyed the Faraday’s law at 900-700°C. The result of XRD measurement after operation, CMF phase were hardly changed after the steam electrolysis. A long-termed durability test was operated, and it revealed that CMF cathode showed the good stability over 90 h at 800 °C. The impedance spectra were measured under applied DC bias potentials. It revealed that polarization resistance and ohmic resistance were decreased with increasing DC bias potential. This decreasing of ohmic resistance was related to the increasing in electronic conductivity of CMF. CMF was n-type semiconductor and then electronic conductivity of CMF increased with decreasing of oxygen partial pressure.

Dielectric relaxation of PVC/PMMA/NiO blends as a function of DC bias

We have prepared poly vinyl chloride (PVC)/poly-methyl methacrylate (PMMA) blend with loading of Nickel oxide (NiO) by solution cast technique. X-ray diffraction reveals the interaction between NiO, PVC and PMMA in the blend form. The weak interaction between PVC, PMMA and NiO was confirmed by Fourier transform infrared spectroscopy. The miscibility of PVC and PMMA has been confirmed by differential scanning calorimetry. The results demonstrate that the 2 wt% NiO loaded PVC/PMMA blend exhibits lowest crystallinity which leads to better NiO dispersion, also observed by atomic force microscopy and scanning electron microscopy. The performance of electrical properties were evaluated under wide band of frequency (10–107 Hz) as a function of DC bias voltage (0–25 V). The dielectric property was characterized via electrical modulus formalism. The present blend systems show good dielectric property as well as considerable conductivity which differs by frequency and DC bias. The variation of AC conductivity as a function of frequency and DC bias shows plateau shape at higher frequency which obeys Jonscher’s power law. It demonstrates that the AC electrical conductivity is directly proportional to the applied DC bias potential. It may be developed for electrolyte application.

Calculation of intrinsic stresses in the diamond-like coatings produced by plasma ion deposition in modes of DC and pulse bias potentials

The formula derivation for calculation of intrinsic stress in diamond-like coatings deposited from the ion flux in modes of continuous and pulsed potentials in view of process of defects formation is given. The criterion of applicability of obtained formula allowing to determine critical parameters of the pulsed potential mode is suggested. Results of calculation of stresses in diamond-like coatings at deposition of low-energy ions C+ from filtered vacuum arc plasma are adduced. The influence of the bias potential, repetition frequency and pulse duration, on the value of intrinsic stress is discussed. Qualitative agreement of calculated stress and experimental data is stated. The important role of deposition temperature in control of intrinsic stress in deposited coating is noted.

Optical Impedance Spectroscopy with Single-Mode Electro-Active-Integrated Optical Waveguides

An optical impedance spectroscopy (OIS) technique based on a single-mode electro-active-integrated optical waveguide (EA-IOW) was developed to investigate electron-transfer processes of redox adsorbates. A highly sensitive single-mode EA-IOW device was used to optically follow the time-dependent faradaic current originated from a submonolayer of cytochrome c undergoing redox exchanges driven by a harmonic modulation of the electric potential at several dc bias potentials and at several frequencies. To properly retrieve the faradaic current density from the ac-modulated optical signal, we introduce here a mathematical formalism that (i) accounts for intrinsic changes that invariably occur in the optical baseline of the EA-IOW device during potential modulation and (ii) provides accurate results for the electro-chemical parameters. We are able to optically reconstruct the faradaic current density profile against the dc bias potential in the working electrode, identify the formal potential, and determine the energy-width of the electron-transfer process. In addition, by combining the optically reconstructed faradaic signal with simple electrical measurements of impedance across the whole electrochemical cell and the capacitance of the electric double-layer, we are able to determine the time-constant connected to the redox reaction of the adsorbed protein assembly. For cytochrome c directly immobilized onto the indium tin oxide (ITO) surface, we measured a reaction rate constant of 26.5 s–1. Finally, we calculate the charge-transfer resistance and pseudocapacitance associated with the electron-transfer process and show that the frequency dependence of the redox reaction of the protein submonolayer follows as expected the electrical equivalent of an RC-series admittance diagram. Above all, we show here that OIS with single-mode EA-IOW’s provide strong analytical signals that can be readily monitored even for small surface-densities of species involved in the redox process (e.g., fmol/cm2, 0.1% of a full protein monolayer). This experimental approach, when combined with the analytical formalism described here, brings additional sensitivity, accuracy, and simplicity to electro-chemical analysis and is expected to become a useful tool in investigations of redox processes.

Methane Recognition and Quantification by Differential Capacitance at the Hydrophobic Ionic Liquid-Electrified Metal Electrode Interface

We present a method to identify and quantify methane using a hydrophobic ionic liquid (IL)–electrified metal electrode interface by electrochemical impedance spectroscopy. We investigated the mechanisms of the responses of the IL-electrified electrode interface to the exposure of methane and other interfering gases (H2, C6H12, SO2, NO, NO2, CO2, O2, H2O). Our results show that at low frequency the IL-electrified electrode interface shows a predominantly capacitive response. The IL-electrode double layer (EDL) was found to be the primary response layer while the transition zone and bulk region of the IL-electrode interface contribute little to the overall signal change. For recognition and quantification of methane using the Langmuir adsorption model and measurement of differential capacitance change, an optimum EDL interface structure was found to form at a specific DC bias potential. The cumulative results shown in this work suggest that an ideal IL-electrode interface can be formed by varying IL structure and applied DC bias electrode potential for a specific analyte and that the semi-ordered structure of IL-electrified interface can act as a recognition element for the sensitive and selective adsorption and detection of gaseous molecules.

Effect of Gamma-Irradiation on Admittance, Suceptance and Conductance of Polyacrylonitrile Gel

We have successfully demonstrated the effect of Gamma-irradiation on Polyacrylonitrile (PAN) gel in terms of admittance (Y), Susceptance (B) and Conductance (G). The trend of Y and B decreases by 297 microSec and 138 microSec respectively and conductance (G) increases by 100 μS. Electrical mechanism associated with microstructure of PAN gel under external DC bias potential is the novelty of this work. External field stimuli responded due to delocalization of charge carriers. These properties are important as novel electronic material.

Effect of dopant and DC bias potential on dielectric properties of polyvinyl alcohol (PVA)/PbTiO 3 - composite films

Composite films of Polyvinyl alcohol (PVA) mixed with Lead Titante Oxide (PbTiO 3) were prepared. Dopant incorporated and DC bias induced electrical parameters were disclosed with respect to pure PVA film. The results demonstrate dielectric polarization is not only directly proportional to PbTiO 3% of dopant but also external DC bias potential at 30 °C based on Maxwell Wagner theory. Hence these properties highly applicable as super-capacitor film and humidity sensor applications.