•Thin films of WOx have been deposited on n- and p-type Si wafers by thermal evaporation technique.•C-V and G-V characteristics of MIS capacitors were studied at different frequencies.•Interfacial ...WOx layer governs the electronic structure of the Si-based MIS structure.•Capacitance peaks in the inversion regimes of Ag/WOx/p-Si confirms the hole response.•The barrier height decreased with a decreasing frequency for both devices.
Tungsten oxide (WOx) thin films were deposited on n- and p-type crystalline silicon (c-Si) wafers by thermal evaporation technique at room temperature. The electrical characterization of Ag/WOx/n-Si and Ag/WOx/p-Si metal–insulator-semiconductor (MIS) capacitors were examined by the capacitance- and conductance-voltage measurements as a function of applied frequency in the 10 kHz 10 MHz range. The admittance properties of both MIS devices have been evaluated by analyzing the interfacial nature and bulk c-Si in accumulation, depletion, and inversion regimes. The capacitance responses of interface traps, bulk c-Si, depletion, and shallow states at the WOx/c-Si interface indicated the appearance of the capacitance peaks in depletion and inversion regimes for Ag/WOx/n-Si and Ag/WOx/p-Si devices. From C-V characterization, various parameters such as the depletion layer width, depletion capacitance, flat-band voltage, total charge density, and net ionized state density were calculated as a function of applied frequency. For Ag/WOx/n-Si device, the total charge density and barrier height values of 7.642 × 10−9 C and 1.119 eV at 1 MHz, respectively, were obtained. The same parameters were calculated to be 5.887 × 10−8 C and 1.107 eV for Ag/WOx/p-Si. The results demonstrated that interfacial nature of WOx film significantly governs the electronic characteristics of the c-Si based MIS devices.
The surface pretreatment of a Ti substrate to produce metal oxide electrodes with electrocatalytic properties is of fundamental importance. The preparation of the substrate prior to the application ...of the coating critically affects the properties of the coating, including its surface roughness, adhesion, and corrosion resistance. In this work, different treatments were applied to the surfaces of Ti discs and their effects on surface roughness were studied. The treatments applied to Ti consisted of three stages: (1) mechanical treatment, (2) degreasing, and (3) chemical treatment. The first stage was carried out with 120 grit SiC abrasive sandpaper, the second stage was carried out with acetone (group A) or sodium hydroxide (NaOH) solution (group B), and the third stage was conducted using hydrochloric acid (HCl), oxalic acid, a mixture of hydrofluoric acid (HF)/phosphoric acid (H3PO4), or a sequence of all three chemical treatments (i.e., HCl, oxalic acid, and HF/H3PO4). The morphological properties, surface composition, and electrochemical behavior of the treated Ti discs were characterized by scanning electron microscopy (SEM), X-ray diffractometry (XRD) and cyclic voltammetry (CV) in a 0.5 M H2SO4 solution, respectively. The electroactive surface area (Aes) and roughness factor (frs) of each Ti disc were estimated from capacitance measurements of the electrochemical double layer. The morphology and voltammetric behavior of Ti varied markedly depending on the surface treatment applied. In addition, the XRD results showed that Ti surfaces subjected to different treatments exhibited different crystallographic planes. The trend in surface roughness with respect to the chemical reagent used was as follows: Group A: oxalic acid > HF/H3PO4 > global treatment > acetone > HCl; Group B: oxalic acid > HF/H3PO4 > NaOH > HCl > global treatment. The most severe chemical attack on the substrate was induced by oxalic acid, which led to the largest electroactive area and roughness factor among the treated Ti samples investigated in this study.
Electrical capacitance tomography (ECT) exhibits several attractive features that are important for industrial process tomography applications. These features include low cost, high speed, and ...nonintrusive nature. However, due to its soft-field character, a relatively low image resolution is an outstanding challenge for ECT. While many efforts have been made to tackle this challenge by improvements in image reconstruction algorithms, relatively less has been done to enhance the basic ECT hardware sensor configuration and data acquisition process. In this paper, a new measurement acquisition strategy is introduced to increase image resolution when using adaptive ECT (AECT). The proposed strategy is based on the manipulation of synthetic electrodes plates ("metaplates") formed by a set of combined smaller physical electrodes (segments). The synthetic electrodes are sequentially activated with partial overlap of constituent segments to provide a fine-stepped axial and/or azimuthal electronic scan along the entire sensor. Consequently, an increased number of independent capacitance measurements are made available. Reconstruction results using the proposed measurement acquisition strategy (AECT) are shown to illustrate the enhanced resolution and stability in the imaging of objects compared to conventional ECT sensors.
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•GO–Fe3O4 nanocomposites/n-Si devices were successfully fabricated.•GO–Fe3O4 nanocomposites/n-Si heterojunction showed good rectifying property.•SCLC conduction was dominated for the ...current transport in the devices.
The graphene oxide–Fe3O4 nanoparticles (GO–Fe3O4) nanocomposites/n-Si heterojunctions were fabricated and their device performance was examined through the analyses of current–voltage (I–V) and capacitance–voltage (C–V) characteristics at room temperature. It was shown that the GO–Fe3O4 nanocomposites were in contact with the n-type silicon (n-Si). The seventeen different gold (Au) contacts performed on the GO–Fe3O4 nanocomposites displayed the identical I–V characteristics. These results revealed that the GO–Fe3O4 nanocomposites were homogeneously coated on n-Si. Under forward bias current–voltage (I–V) conditions, the ohmic and SCLC (space charge limited current) conduction behaviors were identified at low and higher voltages, respectively. Additionally, it was determined that the values of capacitance could be modified with the reverse and forward biases.
•Concentrated Gua forms multilayered architecture on basal-oriented pyrolytic graphite.•Multilayer formation due to Gua-Gua stacking produces GSox peak around 1.1 V.•Less concentrated Gua forms ...planar-arranged network accompanied by peak Gox at 0.8 V.•The multilayered supramolecular architecture was not detected for concentrated Ade.
In this work we experimentally show the formation of a planarly-arranged guanine multilayer on a pyrolytic graphite surface, which was predicted by theoretical calculations at the ideal graphene surface. In the case of adenine, a multilayered architecture like that of guanine was not confirmed. Changes in the purine bases’ arrangement on charged surface in dependence on their concentration is studied using electrooxidation peaks of guanine and adenine, together with time changes in capacitance of electric double layer. Existence of predicted guanine multilayers is supported by electrochemical findings and confirmed by atomic force microscopy. Moreover, our data suggest a link between an additional guanine electrooxidation peak and supramolecular guanine assembly formation.
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Electrical Capacitance Tomography (ECT) exhibits several attractive features which are important for industrial process tomography applications. These features include low cost, high speed, and ...non-intrusive nature. However, due to its soft-field character, a relatively low image resolution is an outstanding challenge for ECT. While many efforts have been made to tackle this challenge by improvements on image reconstruction algorithms, relatively less has been done to enhance the basic ECT hardware sensor configuration and data acquisition process. In this work, a new measurement acquisition strategy is introduced to increase image resolution when using adaptive electrical capacitance tomography (AECT). Here, the proposed strategy is based on the manipulation of synthetic electrodes plates (‘metaplates’) formed by a set of combined smaller physical electrodes (segments). The synthetic electrodes are sequentially activated with partial overlap of constituent segments to provide a fine-stepped axial and/or azimuthal electronic scan along the entire sensor. Consequently, an increased number of independent capacitance measurements are made available. Reconstruction results using the proposed measurement acquisition strategy (AECT) are shown to illustrate the enhanced resolution and stability in the imaging of objects compared to conventional ECT sensors.
The electrostriction phenomenon is observed in membranes of thickness in the nanometer range, e.g. bilayer lipid membranes or self-assembled monolayers. Strong electrical field of 105–106V/cm in ...intensity appears when applying the potential lower than 1V to these membranes. Electrostatic forces change the dimensions of a dielectric, hence the membrane compression and decrease in thickness are observed. As a result, increase in the membrane capacitance is recorded. The presented work covers development and application of a new analytical method based on the innovative capacitance-to-frequency conversion method and flow technique. Construction of the novel flow manifold designed for realization of the whole analytical procedure of chromium(VI) determination with the use of capacitance measurements and its operating rules are shown. The main element of the system is a specially designed measurement cell for realization of chromium determination using a three-electrode system. Au electrode with a self-assembled monolayer of thiols grafted with functional groups selectively interacting with the analyte is employed as a dielectric layer. Ag/AgCl electrode and Pt one are used as a reference and auxiliary electrode, respectively. Accuracy, repeatability and reproducibility of the proposed analytical procedure were tested in determination of Cr(VI) in synthetic solutions and environmental water matrices spiked with the analyte. Benefits and drawbacks of the developed manifold were critically discussed.
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•Novel capacitive sensor for determination of Cr(VI) in water samples is proposed.•Special self-assembled monolayers were developed for electrostriction phenomenon.•Innovative capacitance-to-frequency conversion measurement method was employed.•Flow system was designed to automate the developed procedure.•Performance of the sensor was tested for water samples with a natural matrix.
Organic semiconductor materials have been applied diffusely in photoelectronic devices, such as solar cells, light emitting diodes, etc. Defect states in energy gap are one of most significant ...physical parameters affecting the charge transport in organic devices. Hence, investigating defect states plays a vital role for improving device performance. As one of the most widely applied method of investigating defect states in organic materials, capacitance measurements mainly include capacitance-voltage, capacitance-frequency, forward bias capacitance-voltage and so on, however these measurements have not been comprehensively interpreted and even have not been used properly in detection range. Therefore, in this review, the theory of each capacitance measurement and its application in organic semiconductor are compiled. The comparison of advantages and disadvantages among these different capacitance measurements and detailed description of their detecting range have been carried out. And a following outlook comprising the future developments of capacitance measurement is given. In the end, a table including characteristics for each capacitance measurement is created so as to be understood and used by researchers.
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•The background and theory of each capacitance measurement and its application in organic semiconductor are reviewed.•The comparison of advantages and disadvantages among these different capacitance measurements and detailed description of their detecting range have been implemented.•An outlook comprising the future developments of capacitance measurement is given.•A table including characteristics of each capacitance measurement is made.
•A fully automated capacitive strain sensorboard is developed to improve practical applicability.•A new hardware system is developed for extremely low-level capacitive strain sensing.•A new software ...is developed for fully automated De-sauty bridge balancing, amplification, and shunt calibration.•Performance of the developed sensor board outperformed off-the-shelf high precision capacitance measurement toolkit.
Thin film-based flexible strain sensors have various advantages for structural health monitoring (SHM) because of their capability to sustain large deformations and cover large area of structural surfaces, making them ideal candidates for applications to complex geometries and structural crack monitoring. The authors previously developed a flexible strain sensor technology based on a soft elastomeric capacitor (SEC) for SHM and investigated an alternating current (AC) bridge-based method to transform the strain-induced dynamic capacitance changes in the SEC into analog voltage signals. Previous experiments have verified the capability of the SEC and the AC bridge-based signal converter for structural strain sensing applications. However, careful manipulation requirement for precise AC-bridge balancing, signal amplification control, and shunt calibration limits its practical use for full-scale SHM in field conditions. This study addressed such limitations with critical updates in both hardware and software with fully automated features for high-sensitive capacitive strain sensing. Newly developed hardware and software are fully controlled with a low-cost microcontroller ATmega328p in an automated way. A series of lab tests validated the prototype's performances in the capacitive strain sensing, outperforming an off-the-shelf wired capacitance measurement system (about 34% lower measurement noise), and confirmed that automatic control features worked as designed.
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