Capacitance Spectroscopy Research Articles

Characterization of deep-level defects in highly-doped silicon with asymmetric structure by transient capacitance spectroscopy

Characterization of deep-level defects in highly-doped silicon with asymmetric structure by transient capacitance spectroscopy

Foldamer Nanotubes Mediated Label-Free Detection of Protein-Small Molecule Interactions.

Development of miniaturized lab-on-chip devices for the detection of rapid and specific small molecule-protein binding interactions at very low concentrations holds significant importance in drug discovery and biomedical applications. Here, the label-free detection of small molecule-protein interactions is reported on the surface functionalizable nanotubes of α,γ-hybrid peptide helical foldamers using nanoscale capacitance and impedance spectroscopy. The 12-helix conformation of the α,γ-hybrid peptide observed in the single crystals, self-assembled into nanotubes in an aqueous environment with exposed cysteine thiols for small molecule conjugation. The binding of streptavidin to the covalently linked biotin on the surface of nanotubes was detected at the picomolar concentrations. No change in the capacitance and impedance were observed in the absence of either immobilized biotin or protein streptavidin. The functionalizable hybrid peptide nanotubes reported here pave the way for the label-free detection of various small molecule protein interactions at very low concentrations.

Redoxless Electrochemical Capacitance Spectroscopy for Investigating Surfactant Adsorption on Screen-Printed Carbon Electrodes

Electrochemical impedance spectroscopy (EIS) is a sensitive analytical method for surface and bulk properties. Classical EIS and derived electrochemical capacitance spectroscopy (ECS) with a redox couple are label-free approaches for biosensor development, but doubts arise regarding interpretability when a redox couple is employed (redox EIS) due to interactions between electroactive probes and interfacial charges or forced potential. Here, we demonstrated redoxless ECS for directly determining surfactant adsorption on screen-printed carbon electrodes (SPCEs), validated through a simulation of equivalent circuits and the electrochemistry of electronic dummy cells. Redoxless ECS provides excellent capacitance plot loci for quantifying the interfacial permittivity of di-electric layers on electrode surfaces. Redoxless ECS was compared with redox EIS/ECS, revealing a favorable discrimination of interfacial capacitances under both low and high SDS coverage on SPCEs and demonstrating potential for probeless (reagentless) sensing. Furthermore, the proposed method was applied in an electrolyte without a redox couple and bare electrodes, obtaining a high performance for the adsorption of surfactants Tween-20, Triton-X100, sodium dodecyl sulfate, and tetrapropylammonium bromide. This approach offers a simple and straightforward means for a semi-quantitative evaluation of small molecule interactions with electrode surfaces. Our proposed approach may serve as a starting point for future probeless (reagentless) and label-free biosensors based on electrochemistry, eliminating disturbance with surface charge properties and minimizing forced potential bias by avoiding redox couples. An unambiguous and quantitative determination of physicochemical properties of biochemically recognizable layers will be relevant for biosensor development.

In silico selection of an aptamer for the design of aptamer-modified magnetic beads bearing ferrocene co-immobilized label for capacitive detection of acetamiprid.

In silico evaluation of aptamer/target interactions can facilitate the development of efficient biosensor with high specificity and affinity. In this work, we present in silico, i.e. structural similarity, molecular docking and molecular dynamics selection of the aptamer with sufficient binding properties for acetamiprid (ACE), a nicotine-like pesticide, and its use to design aptamer-modified magnetic beads bearing ferrocene co-immobilized label for capacitive detection of ACE. Taking advantages of the aptamer higher stability and binding affinity, the specific properties of magnetic beads and the redox properties of ferrocene moiety, the developed aptasensor showed promising analytical performances for ACE detection, using electrochemical capacitance spectroscopy, with a linear response ranging from 1fM to 100 pM and a limit of detection of 0.94fM(S/N=3). Furthermore, it was successfully applied to detect ACE in fortified tomatoes samples, proving a promising approach for routine detection of pesticide in real agricultural samples.

Cobalt-Free Layered LiNi0.8Mn0.15Al0.05O2/Graphene Aerogel Composite Electrode for Next-Generation Li-Ion Batteries.

In this work, we introduce LiNi0.8Mn0.15Al0.05O2 (NMA), which is cobalt-free and has a high nickel content, and a conductive composite material to NMA by supporting it with a three-dimensional (3D) graphene aerogel (GA). With an easy freeze-drying approach, NMA nanoparticles are properly dispersed on graphene sheets, and GA creates a strong and conductive framework, significantly improving the structure and conductivity. The structure of the pure NMA and NMA/graphene aerogel (NMA/GA) composite was investigated by X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM). XRD and FE-SEM analyses clearly indicated that ultrapure NMA structures are homogeneously dispersed among the GAs. In addition, the composite structure was examined using transmission electron microscopy (TEM) to determine the dispersion mechanisms. The electrochemical cycling performance of the pure NMA and NMA/GA composite was evaluated by rate capacitance, cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). The synthesized NMA/GA was able to provide 89.81% specific capacity retention after the 500th cycle at C/2. The average charge/discharge rates of the obtained cathode show good electrochemical results and exhibit capacities of 190.2,186.3, 185.2, 176.2, 161.2,142.6, and 188.5 mAh g-1 at C/20, C/10, C/5, C, 3C, 5C, and C/20, respectively. EIS data showed an improvement in the impedance of the composite containing GA. According to the results of the electrochemical tests, NMA nanoparticles formed a conductive network with its porous structure thanks to GA, formed a protective layer on the surface, prevented the side reactions between the cathode and the electrolyte, decreased the impedance of the cathode, and increased the redox kinetics. In addition, the changes in the structure were investigated in the NMA/GA composite cathode by XRD, FE-SEM, and Raman analyses at the end of the 50th, 250th, and 500th cycles. In summary, the NMA/GA cathode is expected to play an important role in lithium-ion batteries (LIBs) by taking advantage of its easy synthesis and excellent cycle stability.

Impedance Spectroscopy Characterization of ZnCo2O4 Ceramics Obtained by the Sol-Gel Method

In this article, structural, morphological and electrical properties of ZnCo2O4 ceramics sample were studied. ZnCo2O4 nanoparticles were synthesized using sol-gel method. Structural and morphological properties of the sample were analyzed using X-ray diffraction and scanning electron microscope. Conductance, capacitance and impedance spectroscopy characterization of ZnCo2O4 ceramics sample were analyzed in 3 kHz-1.5 MHz frequency range and 300-500 K temperature range. Nyquist diagrams of impedance and the equivalent circuit were studied for ZnCo2O4 ceramics in the temperature range of 300-500 K. Cole-Cole curves of the impedance data were found to show a semicircular arc in both low and high temperature areas, which is expressed by the equivalent electrical circuit Rs (RgC g)(RgbQCgb ). Relaxation behavior was identified to be of non-Debye type. The Cole-Cole curve showed the negative temperature coefficient of resistance type behavior. Values of the activation energy corresponding to relaxation processes were found as 0.054 eV below 360 K and 0.561 eV above 360 K.

Non-invasive blood sugar detection by cost-effective capacitance spectroscopy

Abstract. Capacitance spectroscopy is a promising technique for detecting small changes in electrical properties of human blood such as conductivity, permittivity, capacitance, and dielectric constant due to the change of glucose concentration. We studied the capacitance of tissue-mimicking phantoms and the human body, in vitro and in vivo, for detecting blood sugar levels non-invasively by a simple and cost-effective setup. We found that, in tissue-mimicking phantoms, capacitance decreased ∼19 % for glucose concentration increases of 85 % with a correlation coefficient of R2=0.96. In the oral meal tolerance test (OMTT), the body capacitance increased less than 9 % for a 50 % increase in blood sugar level, and it followed the invasive reference with a lag time of ∼25–45 min and semi-invasive reference with a nominal time delay. This lag time is associated with the food digestion time and the diffusion time for the glucose to reach interstitial fluid from blood vessels. We also studied different types of metal pads made of copper, gold-coated copper, and aluminum with various sizes for system optimization. Considering the simplicity, low cost, easy operation, and moderate performance, this capacitive spectroscopy could potentially be a promising technique of detecting blood sugar levels and could be incorporated into other blood sugar detection techniques to reinforce the overall performance.

Thin Films of Polyaniline-Based Nanocomposites with CeO2 and WO3 Metal Oxides Applied to the Impedimetric and Capacitive Transducer Stages in Chemical Sensors.

There is a recognized need for the development of cost-effective, stable, fast, and optimized novel materials for technological applications. Substantial research has been undertaken on the role of polymeric nanocomposites in sensing applications. However, the use of PANI-based nanocomposites in impedimetric and capacitive electrochemical sensors has yet to be understood. The present study aimed to explore the relationship between the sensitivity and linearity of electrochemical pH sensors and the composition of nanocomposites. Thin films of PANI/CeO2 and PANI/WO3 were deposited via spin coating for characterization and application during the electrochemical impedance and capacitance spectroscopy (EIS and ECS) transduction stages. The findings showed that the optimized performance of the devices was extended not only to the sensitivity but also to the linearity. An increase of 213% in the ECS sensitivity of the PANI/CeO2 compared to the metal oxide and an increase of 64% in the ECS linearity of the PANI/WO3 compared to the polymeric sensitivity were reported. This study identified the structure-property relationship of nanocomposite thin films of PANI with metal oxides for use in electrochemical sensors. The developed materials could be applied in devices to be used in different fields, such as food, environment, and biomedical monitoring.

Piezocapacitance spectroscopy of a radiation defect in silicon

In this article, using non-stationary capacitive deep-level spectroscopy (DLTS), the dependence of the parameters of the radiation defect with the ionization energy Ei = Ec − (0.33±0.02) eB arising after irradiation with n − Si · λ - quanta of the 60Co isotope and annealing the samples at 250°C on uniaxial compression was studied. It is shown that, under the action of pressure, Ei ΔEi changes depending on the crystallographic direction and reaches values of 0.06−0.12eB. A comparison is made with a similar effect for the level of the A-centre Ec − 0,17 eB.

Highly sensitive capacitance-based nitrite sensing using polydopamine/AuNPs-modified screen-printed carbon electrode.

Regulatory bodies play a crucial role in establishing limits for food additives to ensure food quality and safety of food products, as excessive usage poses risks to consumers. In the context of processed animal-based foodstuffs, nitrite is commonly utilized as a means to slow down bacterial degradation. In this study, we have successfully leveraged the redox activity of an electrochemically deposited polydopamine (pDA) film onto gold nanoparticle (AuNP)-modified screen-printed electrodes (SPCE) to develop a sensitive and versatile methodology for the detection of nitrite using redox capacitance spectroscopy. By exploiting the interaction of the AuNPs/pDA electroactive interface with the target nitrite ions, we observed distinct changes in the redox distribution, subsequently leading to modifications in the associated redox capacitance. This alteration enables the successful detection of nitrite, exhibiting a linear response within the concentration range of 10 to 500 μM, with a limit of detection of 1.98 μM (S/N = 3). Furthermore, we applied the developed sensor to analyze nitrite levels in processed meats, yielding good recoveries. These results demonstrate the potential of our approach as a promising method for routine detection of ions.

Aptamer-Based Glycated Albumin Sensor for Capacitive Spectroscopy.

Glycated albumin (GA) is a candidate for glycemic indicator to control prediabetes, the half-life of which is about 2 weeks, which is neither too long nor too short, considering that there is no longer any need for daily fingerstick sampling but glucose levels can be controlled in a relatively short term. Its usefulness as a glycemic indicator must be widely recognized by developing a simple and miniaturized GA sensor for point-of-care testing (POCT) devices. In this study, we propose an aptamer-based capacitive electrode for electrochemical capacitance spectroscopy (ECS) to specifically detect GA in an enzyme-/antibody-free manner. As a component of the bioelectrical interface between the sample solution and the electrode, a densely packed capacitive polyaryl film coated on a gold electrode contributes to the detection of GA by the ECS method. In addition, the GA aptamer tethered onto the polyaryl-film-coated gold electrode is useful for not only specifically capturing GA but also inducing changes in the concentration of cations released from the cation/GA aptamer complexes by GA/GA aptamer binding. Also, hydrophilic poly(ethylene glycol) (PEG) coated on the polyaryl film electrode in parallel with the GA aptamer prevents interfering proteins such as human serum albumin (HSA) and immunoglobulin G (IgG) from nonspecifically absorbing on the polyaryl film electrode. Such a GA aptamer-based capacitive electrode produces significant signals of GA against HSA and IgG with the change in GA concentration (0.1, 1, and 10 mg/mL) detected by the ECS method. This indicates that the ECS method contributes to the evaluation of the GA level, which is based on the rate of glycation of albumin. Thus, a platform based on ECS measurement using the aptamer-based capacitive electrode is useful for protein analysis in an enzyme-/antibody-free manner.

Capacitance spectroscopy enables real-time monitoring of early cell death in mammalian cell culture.

Previous work developed a quantitative model using capacitance spectroscopy in an at-line setup to predict the dying cell percentage measured from a flow cytometer. This work aimed to transfer the at-line model to monitor lab-scale bioreactors in real-time, waiving the need for frequent sampling and enabling precise controls. Due to the difference between the at-line and in-line capacitance probes, direct application of the at-line model resulted in poor accuracy and high prediction bias. A new model with a variable range and offering similar spectral shape across all probes was first constructed, improving prediction accuracy. Moreover, the global calibration method included the variance of different probes and scales in the model, reducing prediction bias. External parameter orthogonalization, a preprocessing method, also mitigated the interference from feeding, which further improved model performance. The root-mean-square error of prediction of the final model was 6.56% (8.42% of the prediction range) with an R2 of 92.4%. The culture evolution trajectory predicted by the in-line model captured the cell death and alarmed cell death onset earlier than the trypan blue exclusion test. Additionally, the incorporation of at-line spectra following orthogonal design into the calibration set was shown to generate calibration models that are more robust than the calibration models constructed using the in-line spectra only. This is advantageous, as at-line spectral collection is easier, faster, and more material-sparing than in-line spectra collection.

Effects of the potential and the electrolyte nature in the integrity of the O-(2-Mercaptoethyl)-O′-methyl-hexa(ethylene glycol) self-assembled monolayer by electrochemical impedance spectroscopy

• Electrochemical impedance spectroscopy in the absence of redox probes informs about the integrity of the monolayer. • The EG7-SAM resists the ingress of ions under certain experimental conditions. • The stability region of the EG7-SAMs is lower when defined by impedance in comparison with cyclic voltammetry. • The nature of the electrolyte and the solution pH influence the ability of ion ingress in the EG7-SAM. • Capacitance spectroscopy adds more insight into the EG7-SAM behavior in respect to ions conduction through the film. This work addresses an in-deep study of the ionic conductive properties of the O-(2-Mercaptoethyl)-O’-methyl-hexa(ethylene glycol)-self assembled monolayer (EG7-SAM) by electrochemical impedance spectroscopy in a range of experimental conditions including different aqueous electrolytes and wide potential intervals. The measurements are made in the absence of electroactive probes to get information about the ionic ingress or dynamics into the film. The SAMs stability potential regions comprised between both the potentials for reductive and oxidative desorption processes are here limited and re-defined as regions where ionic ingress occur and these where the ionic permeability does not take place. This distinction leads to a much smaller region where the SAM behaves as an ideal capacitor. Moreover, these features are dependent on the solution pH and electrolyte in contact with the SAM. The temperature effects on the ionic conductivity are also addressed resulting in differences in behavior of complementary parameters. Capacitance spectroscopy analysis of the EG7-SAM helps in the characterization of these films. Thus, information about processes occurring in different time scales (or frequencies) is obtained through the proposed analysis. Putting all the results together, a new perspective of the SAMs conductive properties can be obtained that will be very useful in the choice of a determined layer for specific applications.

Charge Trap States of SiC Power TrenchMOS Transistor under Repetitive Unclamped Inductive Switching Stress.

Silicon carbide (SiC) has been envisioned as an almost ideal material for power electronic devices; however, device reliability is still a great challenge. Here we investigate the reliability of commercial 1.2-kV 4H-SiC MOSFETs under repetitive unclamped inductive switching (UIS). The stress invoked degradation of the device characteristics, including the output and transfer characteristics, drain leakage current, and capacitance characteristics. Besides the shift of steady-state electrical characteristics, a significant change in switching times points out the charge trapping phenomenon. Transient capacitance spectroscopy was applied to investigate charge traps in the virgin device as well as after UIS stress. The intrinsic traps due to metal impurities or Z1,2 transitions were recognized in the virgin device. The UIS stress caused suppression of the second stage of the Z1,2  transition, and only the first stage, Z10, was observed. Hence, the UIS stress is causing the reduction of multiple charging of carbon vacancies in SiC-based devices.

Nickel nanobrush platform for a magnetic field-assisted electrochemical response enhancement

A single-step electrochemical procedure to synthesize a brush-like platform, which composed of a nickel nanowire array attached to a nickel continuous layer acting as a solid base, is described. Room temperature hysteresis properties of this brush-like architecture (nanobrush) and those of the individual components (nanowires and layer) are determined. It is shown that the direction of the nanobrush magnetic easy axis may be tailored, being also possible to control the magnetic system's coercivity and remanence. The electrochemical response and the catalytic activity of a Ni nanobrush towards the redox probes [Fe(CN) 6 ] 4-/3- and ethanol were evaluated in the presence and absence of an applied magnetic field. The external field strongly affects the system's behavior by enhancing the electrode charge-transfer response, even at fields as low as 6 mT. This improvement was further investigated by Electrochemical Impedance Spectroscopy and Electrochemical Capacitance Spectroscopy studies. It is concluded that the enhanced electrochemical charge-transfer process of the Ni nanobrush electrode, with a magnetic field applied along the Ni nanowires axis, arises from a larger electroactive area. • A Ni nanobrush electrode is obtained by a single step electrodeposition route. • Nanobrush architecture consists of Ni NWs perpendicularly attached to a Ni layer. • The whole platform easy axis orientation is controlled by the brush shape and crystalline texture. • Catalytic activity towards redox probes Fe(CN) 6 −4/−3 and ethanol are evaluated. • A small magnetic field drastically reduces the nanobrush impedance.

A new approach to in-situ Co3O4 nanostructure decorated free-standing carbon foam derived from phenolic resin for high-performance supercapacitor

Herein, a novel method to fabricate a cobalt oxide (Co3O4) nanostructure decorated with lightweight free-standing carbon foam (CF) has been reported. Primarily, the freestanding CF was fabricated via a polyurethane (PU) foam replica method using phenolic resin, followed by oxidation stabilization and finally carbonization at 1000 ºC in an inert atmosphere. After that different contents of Co3O4 nanoparticles (NPs) were decorated on free-standing CF using the in-situ hydrothermal method. The developed foams have been extensively studied for various electrochemical characteristics including cyclic voltammetry (CV), capacitance, and electrochemical impedance spectroscopy (EIS) in 1 M KOH solution using a three-electrode system. The structural and morphological investigation of foams was examined by XRD, Raman, and SEM. It is observed that Co3O4 NPs are uniformly decorated on CF and the electrochemical performance of CF is improved synergistically. Consequently, the specific capacitance (302 F g−1 at mV s−1) was greatly enhanced when the CF was decorated with 10 % Co3O4 NPs. Moreover, an asymmetrical two-cell supercapacitor composed of CF-10Co3O4 positive electrode and CF negative electrode exhibited a specific capacitance of 164 F g−1 at a current density of 0.5 A g−1. The device (CF-10Co3O4//CF) can deliver a high energy density of 44 Wh kg−1 at the power density of 350 W kg−1. The high specific capacitance and large energy density demonstrate the potential application of carbon-Co3O4 decorated foams in compact and lightweight supercapacitors.

Porous 3D-graphene functionalized with MnO2 nanospheres and NiO nanoparticles as highly efficient electrodes for asymmetric capacitive deionization: Evaluation by impedance-derived capacitance spectroscopy

Capacitive deionization (CDI) is a novel desalination technology for brackish water purification. Here, we report the rational design of an efficient asymmetric CDI system considering several steps. First, three-dimensional graphene nanostructures (3DG) were synthesized using the hydrothermal method, followed by the freeze-drying process, and then drop casting onto the carbon fiber paper (CFP) substrate. Second, a facile and controllable electrodeposition technique was used for the in-situ synthesis of MnO2 nanospheres and NiO nanoparticles onto the CFP/3DG surface to prepare CFP/3DG/MnO2 cathode and CFP/3DG/NiO anode. Third, the prepared nanocomposite electrodes were used to fabricate an asymmetric CDI cell. Here, MnO2 (pI = 4.5) and NiO (pI = 10) nanostructures provide opposite surface charges due to their dissimilar isoelectric points, enhancing cations and anions electrosorption. The surface morphology, chemical and electrochemical characteristics, as well as the capacitive performance of the fabricated CFP/3DG/MnO2 and CFP/3DG/NiO electrodes, were investigated using SEM, EDX, XRD, FTIR, TGA, BET/BJH, and electrochemical techniques. Besides, impedance-derived capacitive analysis was used to evaluate the ions retention time on the fabricated electrodes. Finally, the fabricated CFP/3DG/NiO||CFP/3DG/MnO2 asymmetric CDI cell was used in water desalination with high reversibility, good regeneration rate, and high electrosorption capacity (21.01 mg g−1) for the initial salt concentration of 1000 mg L−1 in 1.2 V. These results suggest that the proposed asymmetric CDI system is a promising candidate for the efficient capacitive desalination process.

Determination of the charge carrier density in organic solar cells: A tutorial

The increase in the performance of organic solar cells observed over the past few years has reinvigorated the search for a deeper understanding of the loss and extraction processes in this class of device. A detailed knowledge of the density of free charge carriers under different operating conditions and illumination intensities is a prerequisite to quantify the recombination and extraction dynamics. Differential charging techniques are a promising approach to experimentally obtain the charge carrier density under the aforementioned conditions. In particular, the combination of transient photovoltage and photocurrent as well as impedance and capacitance spectroscopy have been successfully used in past studies to determine the charge carrier density of organic solar cells. In this Tutorial, these experimental techniques will be discussed in detail, highlighting fundamental principles, practical considerations, necessary corrections, advantages, drawbacks, and ultimately their limitations. Relevant references introducing more advanced concepts will be provided as well. Therefore, the present Tutorial might act as an introduction and guideline aimed at new prospective users of these techniques as well as a point of reference for more experienced researchers.

Capacitance spectroscopy of thin-film formamidinium lead iodide based perovskite solar cells

This work concerns the interpretation of capacitance spectroscopy results in perovskite-based solar cells. Based on the deep level transient spectroscopy and admittance spectroscopy results, we present arguments that the observable signals in perovskite-based solar cells come from anion migration rather than being a response from deep trap energy levels. The ion migration parameters, such as activation energy and ion concentration, are calculated and compared to theoretical values for different migration paths of ions in perovskites. Those parameters evolve with time, reflecting in the degradation of the cells, which we propose to link with a change in the anion migration path in perovskite. • The same signal is observed in DLTS and admittance spectroscopy. • Its activation energy is in the 0.3 eV–0.5 eV range and decays with time. • Time constants and the presence of large capacitance transients at +1 V point into the diffusion related origin of the signals. • Low activation energy, DLTS sign, comparison with other experiments and theoretical calculations point into anion diffusion. • The observed, dominating signal correlates with the increased shunt of the device.

Bilayer WSe2 as a natural platform for interlayer exciton condensates in the strong coupling limit.

Exciton condensates (ECs) are macroscopic coherent states arising from condensation of electron-hole pairs1. Bilayer heterostructures, consisting of two-dimensional electron and hole layers separated by a tunnel barrier, provide a versatile platform to realize and study ECs2-4. The tunnel barrier suppresses recombination, yielding long-lived excitons5-10. However, this separation also reduces interlayer Coulomb interactions, limiting the exciton binding strength. Here, we report the observation of ECs in naturally occurring 2H-stacked bilayer WSe2. In this system, the intrinsic spin-valley structure suppresses interlayer tunnelling even when the separation is reduced to the atomic limit, providing access to a previously unattainable regime of strong interlayer coupling. Using capacitance spectroscopy, we investigate magneto-ECs, formed when partially filled Landau levels couple between the layers. We find that the strong-coupling ECs show dramatically different behaviour compared with previous reports, including an unanticipated variation of EC robustness with the orbital number, and find evidence for a transition between two types of low-energy charged excitations. Our results provide a demonstration of tuning EC properties by varying the constituent single-particle wavefunctions.