Thickness Of Space Charge Layer Research Articles

Correlative study of Mott–Schottky analysis and corrosion behaviour of plasma electrolytic oxidation treated magnesium alloy: Effect of Cl⎺ concentrations

Semiconducting and corrosion properties of the plasma electrolytic oxidation treated AM50 magnesium alloy was correlatively investigated as a function of Cl⎺ content. Semiconducting character transitioned from p – type (for 0.01 M Cl⎺) to n – type (for both 0.1 and 1 M Cl⎺). Corrosion potential moved progressively to noble potential with the increase in Cl⎺ content. Variations of impedance modulus at lowest frequency employed (|Z|0.1 Hz), resistance of inner barrier layer (RIL), and corrosion current density with the Cl⎺ content were correlated with the variations of the defect density, change in Ecorr – Efb. and thickness of space charge layer.

Cathode sheath parameters and their influences on arc root behavior after liquid metal bridge rupture in atmospheric air

The cathode sheath (CS) formation of the direct current air circuit breaker is simulated by a fluid model, and the influence of metal vapor concentration between the contacts after liquid metal bridge rupture is considered. The CS conductivity increases with the increasing concentration of copper vapor. The copper vapor concentration increases from 5% to 95%, and the thickness of the positive space charge layer and ionization layer increases from 22.3 and 49.1 μm to 51.8 and 81.7 μm, respectively. Increasing the CS conductivity is beneficial for the motion of arc roots in a certain range.

Modeling of space charge dynamics in polyethylene under AC stress based on bipolar charge transport model

Space charge dynamics under AC stress is of importance as a majority of high voltage cables are under AC stress, and space charge is the driving mechanism of dielectric degradation under these conditions. Bipolar charge transport model is used to simulate space charge dynamics in polyethylene under AC stress. The current density, electroluminescence intensity and space charge density under sinusoidal, triangular and square voltages are compared. It is found that there is no phase shift between current density, electroluminescence intensity and applied voltages, which disagrees the results of Baudoin et al. The thickness of space charge layer under AC stress is much thinner that under DC stress.

The effects of W/Mo-co-doped BiVO4 photoanodes for improving photoelectrochemical water splitting performance

The poor electrical conductivity of bismuth vanadate (BVO) can be improved by metal-doping at optimum percentage. Previously, we improved the photoelectrochemical (PEC) properties of BVO photoanodes by optimizing the different atomic percentage of molybdenum (Mo). Here, we co-doped BVO simultaneously with tungsten/molybdenum (W/Mo) to enhance the water splitting properties of BVO photoanodes. At optimum co-doping percentages of 0.5 %W-2%Mo BiVO4 (0.5W-2Mo-BVO) the photocurrent density maximum was ∼ 0.97 mA cm−2 at 0.6 V vs. Ag/AgCl. The water splitting was performed under 100 mW. cm-2 irradiation and 0.6 V vs. Ag/AgCl applied voltage for 0.5W-2Mo-BVO. The H2 production was 19.5 μmol.cm-2 after 2 h at optimized W/Mo co-doping. W/Mo co-doping into BiVO4 greatly improved the electron mobility, as demonstrated by photocurrent, Mott-Schottky, electrochemical impedance, open circuit potential (ΔOCP) and incident photon conversion efficiencies (IPCE) measurements. As compared to pure BVO, 0.5W-2Mo-BVO showed ∼2700-fold increase in the donor concentration (ND) and greatly decreased (1/60) space charge layer thickness (WSCL), which induced efficient charge carrier mobility and enhanced the PEC performance.

A NOVEL METHOD FOR STUDYING THE CORROSION RESISTANCE AND MICROSTRUCTURE OF ENAMEL COATING MODIFIED ON HIGH-STRENGTH STEEL IN 3.5 wt.% NaCl SOLUTION

A new method was introduced to research the corrosion resistance of enamel coatings which were sintered at different temperatures in this paper. 1 – 4 Scanning electrochemical microscopy (SECM) conjunction with capacitance-potential test and Mott–Schottky analysis technique were used to study the coating failure process and semiconductor conduction behavior of enamel coating in 3.5[Formula: see text]wt.% NaCl solution. The high strength steel (SAPH440) was selected as the metal substrate. The coatings which were sintered at different temperatures on the high strength steel were analyzed and their corrosion behaviors and microstructures were also measured by potentiodynamic polarization curves, Mott–Schottky analysis technique and scanning electrochemical microscopy. 5 – 10 In this paper, five kinds of enamel coatings were prepared on high strength steel. The SECM results show that the Faraday current of the microprobe tip gradually decreases with the soaking time increasing, which indicates that the coatings become failure slowly with the invasion of water and aggressive ions. At the same time, the tip current was homogeneous during the immersion process, which reflected that the surface of the sample remained stable, no obvious bulges appeared. Capacitance–potential test and Mott–Schottky analysis 7 , 8 show that the external ions and water molecules gradually penetrate into the coating; coating showed characteristics of [Formula: see text]-type semiconductor as time increases, the capacitance increases gradually, the space charge layer thickness decreases, slope of Mott–Schottky curve decreased gradually which indicates that the failure of coating in the process of soaking slowly with the charge carrier density increases.

Enhanced photocatalytic activity towards H2 evolution over NiO via phosphonic acid surface modification with different functional groups

Enhancing the photocatalytic activity of NiO towards hydrogen generation (6 times) is achieved by phenyl phosphoric acid (PPA) surface modification. The photocatalytic activity can be further improved by changing PPA to 4-aminophenyl phosphonic acid (PPA-NH2), about 10 times, suggesting the functional group plays an important role in improving the activity. A chemical bond (NiOP) between NiO and organic phosphoric acid was proved by FT-IR spectra. XPS and LSV analysis suggested organic phosphonic acid modification increased the electron density of Ni, which promoted the transformation from Ni2+ to Ni0. Mott-Schottky (M − S) measurement revealed that PPA-NH2 modified NiO processed a larger the space charge layer thickness (dsc), which enhanced ability towards H2 evolution from dynamical aspect.

Calculation of the Space Charge Layer Thickness with Account for the Dipole Moment of Water Molecules in KCl and NaCl Solutions

The problem of the electric double layer in electrolytes is considered. The Poisson equation is integrated with account for the screening of electrodes by salt ions and water molecules. The space charge layer has been calculated. The volt–ampere characteristics in NaCl and KCl solutions are presented. A method for determining the temperature of ions from the volt–ampere characteristic of the electrolyte solution is proposed.

The space charge layer thickness calculation in NaCl and KCl water solutions

The space charge layer thickness calculation in NaCl and KCl water solutions

Electrochemical Pore Formation in InP: Understanding and Controlling Pore Morphology

Research on semiconductor nanostructures is motivated by two key considerations. The first is the continuing call for smaller and more efficient versions of existing semiconductor devices. The second is the characterisation and exploitation of the unique characteristics that are often exhibited by structures at the nano-scale. While a wide variety of semiconductor nanostructures can be produced without difficulty (e.g. by self-assembly or preferential etching), precise control over the morphology of these structures is often much harder to achieve. The electrochemical formation of nano-scale porosity in semiconductors has been studied extensively1-5 and has found some application due to its bulk characteristics e.g. the use of porous silicon as a passivation layer6. However, the exploitation of the nano-scale properties of these structures is unlikely until a comprehensive understanding of the factors affecting pore morphology has been obtained. We have previously demonstrated7-9 the formation of nano-scale porosity in n-type InP anodised in KOH. Pores emerge form pits in the electrode surface10 and grow and branch along the <111>A crystallographic directions9 forming tetrahedral porous domains8. Under certain conditions, current-line oriented pores can also be obtained.11 In order to understand the factors effecting pore morphology, porous InP was formed under a range of different temperatures, electrolyte concentrations, carrier concentrations and current densities. The morphology of the resulting porous layers was analysed in detail. In particular, the pore width, layer thickness and porosity of the layers were all measured. We show that at low current densities, the pore width is dominated by the magnitude of the current density. At higher current densities, we show that both the pore width and the porosity are inversely related to the kinetics of the electrochemical reaction: the pore width being lowest at high temperatures and intermediate KOH concentrations. The pore width decreases with increasing carrier concentration, which is likely due to the associated decrease in the space charge layer thickness. Porosity varies in a similar manner to pore width and the maximum porous layer thickness is correlated to the pore width in all cases. These results support a model9of pore formation based on competition in kinetics between hole supply at the pore tip and the electrochemical reaction at the semiconductor electrolyte interface. It will be shown that this model makes the correct qualitative predictions for the variation of pore morphology with temperature, electrolyte concentration, carrier concentration and current density. Such an understanding of the factors affecting the morphology of these porous layers is an essential step in achieving the process control necessary for them to be integrated into standard semiconductor fabrication techniques.

Use of Surface Photovoltage Spectroscopy to Measure Built-in Voltage, Space Charge Layer Width, and Effective Band Gap in CdSe Quantum Dot Films.

Surface photovoltage spectroscopy (SPS) was used to study the photochemistry of mercaptoethanol-ligated CdSe quantum dot (2.0-4.2 nm diameter) films on indium doped tin oxide (ITO) in the absence of an external bias or electrolyte. The n-type films generate negative voltages under super band gap illumination (0.1-0.5 mW cm(-2)) by majority carrier injection into the ITO substrate. The photovoltage onset energies track the optical band gaps of the samples and are assigned as effective band gaps of the films. The photovoltage values (-125 to -750 mV) vary with quantum dot sizes and are modulated by the built-in potential of the CdSe-ITO Schottky type contacts. Deviations from the ideal Schottky model are attributed to Fermi level pinning in states approximately 1.1 V negative of the ITO conduction band edge. Positive photovoltage signals of +80 to +125 mV in films of >4.0 nm nanocrystals and in thin (70 nm) nanocrystal films are attributed to electron-hole (polaron) pairs that are polarized by a space charge layer at the CdSe-ITO boundary. The space charge layer is 70-150 nm wide, based on thickness-dependent photovoltage measurements. The ability of SPS to directly measure built-in voltages, space charge layer thickness, sub-band gap states, and effective band gaps in drop-cast quantum dot films aids the understanding of photochemical charge transport in quantum dot solar cells.

Hydroxyl defect effect on the resistance degradation behavior in Y-doped (Ba,Ca)(Ti,Zr)O3 bulk ceramics

Degradation behavior of acceptor (Y)-doped (Ba,Ca)(Ti,Zr)O3 ceramics sintered in moist reducing atmosphere and subsequently re-oxidized in dry or wet atmospheres was contrasted. The degradation behavior critically depends on the water vapor incorporation, the time to degradation systematically decreased with the incorporation of hydroxyl defects (OH)O•. The electrical conductivity was investigated by means of impedance spectroscopy (IS) to determine properties, such as grain and grain boundary conductivity, grain boundary potential barrier height, and space charge layer thickness. Furthermore, transmission electron microscopy (TEM) and electron energy loss spectroscopy (EELS) were applied to consider microstructure, microchemistry, and oxygen stoichiometry changes.

Investigation of Mott–Schottky Analysis Test Parameters to Study the Semiconductive Properties of Passive Films of Carbon Steel in Highly Alkaline Environments

Abstract A testing methodology for using Mott–Schottky (M-S) analysis to study the semiconductive properties of passive films that form on carbon steel in simulated concrete pores solutions (pH &amp;gt; 12.5) is presented. The development of the methodology includes determining the proper M-S potential sweep range, rate, and frequency for the passive steel, which were found to be −0.5 to 0.5 V, 18 mV/s, and 1000 Hz, respectively. The methodology was then applied to steel rebar in a saturated calcium hydroxide passivating solution (pH 12.6) to simulate the highly alkaline environments seen in concrete. Potentiostatically formed passive film was different from the film formed under open-circuit conditions. The passive film on steel rebar was found to be n-type with two discrete donor species. A donor density on the order of 1021 cm−3, a flatband potential of −0.53 V, and a maximum space charge layer thickness of 0.4 nm at full passivation were reported.

Transient Phenomena in Probe Measurements in Low-Density Helium and Oxygen Plasma

Measurements of the probe characteristics in the pulsed mode in oxygen and helium plasma are presented. The question on the thickness of the near-probe space charge layer in the electron–ion, electron–ion–ion, and ion plasma is discussed. It has been shown that the presence of negative ions in the plasma leads to a drastic decrease in the thickness of the ion layer. A model of the formation of a near-probe layer in nonstationary low-pressure plasma is proposed. It been shown that a space charge layer is formed in the time of 5–6 collisions of ions with neutral particles. It has been illustrated that the displacement current has a linear dependence on the potential applied to the probe. The question concerning the value of the dielectric constant of the plasma is discussed.

Measuring the Thickness and Potential Profiles of the Space-Charge Layer at Organic/Organic Interfaces under Illumination and in the Dark by Scanning Kelvin Probe Microscopy

Scanning Kelvin probe microscopy was used to measure band-bending at the model donor/acceptor heterojunction poly(3-hexylthiophene) (P3HT)/fullerene (C60). Specifically, we measured the variation in the surface potential of C60 films with increasing thicknesses grown on P3HT to produce a surface potential profile normal to the substrate both in the dark and under illumination. The results confirm a space-charge carrier region with a thickness of 10 nm, consistent with previous observations. We discuss the possibility that the domain size in bulk heterojunction organic solar cells, which is comparable to the space-charge layer thickness, is actually partly responsible for less than expected electron/hole recombination rates.

Study of the semi-conductive behavior of the passive film on carbon steel in simulated concrete pore solution under stress

Purpose – This paper aims to clarify the semi-conductive behavior of the passive layer formed in concrete environment without and with presence of chloride ions under different loading conditions. Passivation and depassivation of steel play an essential role in the subsequent stages of the corrosion process. Due to the nature of passive films on metals, they show electrochemical properties of a semi-conductor. Design/methodology/approach – A C-ring model was proposed in this experiment to induce stress on the specimens. Specimens under different levels of compressive and tensile loadings were exposed to chloride-free and chloride-contaminated solutions and their semi-conductive behavior was investigated using Mott–Schottky technique. Findings – Irrespective of the type and magnitude of the applied load, the passive film on rebars in simulated concrete pore solution is a highly disordered n-type semi-conductor. In all specimens, the presence of chloride ions decreases the slope of the Mott-Schottky plots, the donor density and the space charge layer thickness, which leads to a thinner passive film. Results indicate that steel specimens immersed in chloride-free pore solution under tensile loadings passivate more rapidly compared to those under compressive loadings. However, the situation in chloride-contaminated solution is different, and steel under tensile stress exhibits more corrosion than steel under compressive stress or under no load. Originality/value – Reinforced concrete structures inevitably experience variable mechanical loads, and continuous degradation from aggressive environments. Therefore, it is imperative to study the synergic impact of different types of mechanical loadings and exposure to chloride ions on this process. This paper fulfils this need.

New relationships of dark diffusion and recombination currents as a function of temperature for a crystalline cell photovoltaic

The effects of temperature and solar radiation on the characteristic p-n junction solar cells are investigated theoretically. The two-diode model is represented in this paper. This model requires only five parameters (the photocurrent, the shunt resistance, the series resistances, the diffusion, and the recombination dark current). The analytical resolution of continuity equations in each region of a crystalline solar cell, including the intrinsic carrier concentration, the energy band gap and the thickness of space charge layer as function of temperature, allowed us to determine the expressions of diffusion and recombination dark currents. We propose new relationships giving the expressions of these currents as a function of their reference values which are determined from both the data provided by the manufacturer and the different temperature values. To validate the accuracy of the proposed model, we compared predicted current–voltage curves with model double-diode model of Ishaque et al. and experimental data from various manufactures for two different cell technologies (single crystalline, poly crystalline). We determine the maximum power calculated by our proposed model to compare by double-diode model of Ishaque et al. for two cell type at the five conditions of generation rate. Generally, our model shows a better agreement with the experimental data than the Ishaque one. Our proposed work is useful because it provides to manufacturers an easy and comprehensive study to know the variation of the maximum power delivered by the photovoltaic module as a function of temperature and generation rate.

Effects of MoS2 thickness and air humidity on transport characteristics of plasma-doped MoS2 field-effect transistors

The authors present a study on transfer characteristics of plasma-doped MoS2 transistors with various MoS2 thicknesses and those acquired under different air humidity conditions. The MoS2 thickness-dependent characterization implies that plasma-assisted doping processes induce p-doping to multilayer MoS2 channels through a surface-charge-transferlike mechanism and the effective space-charge layer thickness is estimated to be ∼22 nm. The humidity-dependent characterization shows that plasma-doped MoS2 transistors exhibit a much more prominent dependence of the transfer characteristics on humidity in comparison with pristine MoS2-based transistors. This is attributed to the plasma-induced dangling bonds or absorbate centers on MoS2 surfaces, which can enhance the absorption of water molecules and result in additional p-doping to MoS2 transistors. This work advances the understanding of the effects of plasma doping processes on the electronic properties of MoS2 and provides important technical insights for making MoS2-based gas and chemical sensors.

Interfacial phenomena between lithium ion conductors and cathodes

Nanocomposites of a lithium ion conductor Li 1.3 Al 0.3 Ti 1.7 (PO 4 ) 3 and electrode materials (TiO 2 and FePO 4 ) were prepared to investigate interfacial structure and ionic conductivity at the interface between the solid electrolyte and electrode materials. It was revealed that lithium ions in the solid electrolyte were attracted to the cathode materials with increasing electrode potential, which increases lithium vacancies in the solid electrolyte. For the FePO 4 containing composites, due to the high electrode potential, lithium transfer across the interface and ionic conduction through the cathode materials was remarkable. The results suggest that severe lithium depletion occurs and interfacial resistance is large at the interface of high ionic conductors and cathode materials. The space charge layer thickness is also discussed. • Nanocomposites of lithium ion conductors and electrode materials were fabricated. • Conductivity enhancement depended on charge carriers and cathode potentials. • High potential cathodes cause lithium depletion in high ionic conductors. • All the results were well explained with the space charge layer model.

Electric characterization of grain boundaries in ionic conductors by impedance spectroscopy measurements in a bicrystal

Here we show impedance spectroscopy measurements on a bicrystal of the ionically conducting yttria stabilized zirconia (YSZ). By using micrometer sized electrodes it is possible to measure ionic transport perpendicular to a single grain boundary, and characterize its electrical properties. We are thus able to obtain the microscopic parameters that determine the charge distribution at the grain boundary and the ionic transport through it, as the potential energy barrier ΔΦ = 0.35±0.01 V at 275 oC, and the space charge layer thickness λ* = 5±1 A. These values are significantly different from those previously obtained in polycrystalline ceramic samples of the same material, and show much better agreement with the values predicted by the Mott-Schottky model for the charge distribution and ionic transport through the grain boundary.

Electrochemical Impedance Investigation of Anodic Alumina Barrier Layer

In the present work, well ordered nanoporous anodic aluminum oxides (AAO) have been prepared on aluminum by a two step anodization process in 0.5 M oxalic acid at various potentials. We report the properties and semiconducting characteristics of the porous alumina barrier layers by electrochemical impedance spectroscopy analysis (EIS). EIS is considered to be a highly sensitive and non-destructive technique that allows determining barrier oxide layer characteristics. Aluminum oxide barrier is considered as a semiconductor which acts as a p-n heterojunction at anodizing voltages up to 20 V. The alumina barrier layer structure consists of a hole transport inner layer and an electron transport outer layer. Doping densities, flatband potential as well as space charge layer thickness are discussed in correlation with anodizing potential. Barrier layer thicknesses measurements obtained by EIS were compared with those obtained after EIS measurements by direct scanning electron microscopy observations.