Thickness Of Space Charge Layer Research Articles

The Influence of Cold Working on Semiconducting Properties of Passive Film and Pitting Corrosion Resistance of High Nitrogen Austenitic Stainless Steel

The effect of cold working on semiconducting properties of passive film and pitting corrosion resistance of 19Cr-18Mn-2Mo-0.9N high nitrogen austenitic stainless were investigated by anodic polarization, AC impedance and capacitance measurement methods. With increasing the cold rolling deformation ranging from 0% to 60%, the passive region of high nitrogen austenitic stainless steel decreases, and the corrosion potential, EIS radius and polarization resistance all decreases. The Mott-Schottky result indicates that the pitting corrosion resistance deteriorates with increment of cold rolling deformation. The results show that the passive films formed on high nitrogen austenitic stainless steel with different cold rolling deformation behave as n-type semiconductors. With increasing the cold rolling deformation grade, the donor density (ND) increases, but the thickness of the space-charge layer (W) decreases. The decreasing of the thickness of space-charge layer with increment of cold rolling deformation is attributed to the inceasing defect which deteriorates the stability of the passive film.

Properties of the Passive Film on Alloy 22 in Chloride Solutions Obtained by Electrochemical Impedance

Impedance measurements were performed for alloy 22 in the passive and transpassive range, in 1 M NaCl at 90°C. A RΩ-(R//CPE) circuit model was applied in the full passive range, where R was the film resistance. This model also applied for a wide range of chloride concentrations and pH values, at the open circuit potential. Two time constants were observed at the beginning and at the end of the passive range. In these cases, the resistances for the ion transfer might be located at the film interfaces, and not in the film itself. The protective properties of the film improved with polarization time due to the thickening and ageing of the film. The film resistance and the space charge layer thickness increased with the potential. The oxidation of Cr3+ to Cr6+ occurred in the film at high potentials, followed by the transpassive dissolution. In the pre-transpassive range of potentials, the film showed a p-type electronic character, while the ionic properties were that of a passive film. The passive film of alloy 22 was an n-type semiconductor, which changed to a p-type for the high passive potentials. ND = 2.7 × 1020 cm−3 and EFB = −0.551 VSCE were determined.

A 3D model for thickness and diffusion capacitance of emitter-base junction determination in a bifacial polycrystalline solar cell under real operating condition

This paper aims at presenting the behaviour of the space charge region for an n^+-p-p^+ bifacial solar cell under monochromatic illumination. It also deals with mathematical relations in the describing and the use of new approach that involves both junction and back surface recombination velocities with a 3D modelling study. Based on the normalized carriers' density, versus base depth, the space-charge layer thickness (Z_{0,u}) is studied for various parameters such as grain size g, grain boundaries recombination velocity S_{gb}, wavelength \lambda and for different operating conditions. Therefore, the relationship between Z_{0,u} and the diffusion capacitance C_u show that junction in the n^+-p-p^+ solar cell, with columnar grain orientation, is characterized by the plane capacitor properties.

Ionization behavior of deep level donors in passive film formed on surface of stainless steel in 5% salt solution

Deep level donor's ionization behavior of passive film formed on the surface of stainless steel was investigated by Mott-Schottky plots. It is indicated that transformation process of deep level donors' ionization behavior of passive film on surface of stainless steel can be divided into 4 stages with rising immersion time. At the initial immersion stage (10 min), Fe(Ⅱ) located in the octahedral sites of the unit cell is not ionized and the deep level does not appear in Mott-Schottky plots. At the second stage (9−38 h), Fe(Ⅱ) located in the octahedral sites starts to be ionized, which results in deep level donors' generation and density of deep level donors almost is constant with augmenting immersion time but the thickness of space charge layer is more and more thicker with rising immersion time. At the third stage (48 h−12 d), density of deep level donors rises with increasing immersion time and the thickness of passive films space charge layer decreases. At last stage (above 23 d), both the space charge layer's thickness and density of deep level donors are no longer changed with increasing immersion time. In the overall immersion stage, the shallow level donors' density is invariable all the time. The mechanism of deep level donor's ionization can be the generation of metal vacancies, which results in crystal lattice's aberration and the aberration energy urges the ionization of Fe(Ⅱ) in octahedral sites.

Space–charge theory applied to the grain boundary impedance of proton conducting BaZr 0.9Y 0.1O 3 − δ

The specific grain interior and grain boundary conductivities, obtained from impedance spectroscopy and the brick layer model, are reported for BaZr 0.9Y 0.1O 3 − δ as a function of p O 2 and temperature. p O 2 -dependencies were indicative of dominating ionic and p-type electronic conduction for the grain interior under reducing and oxidizing conditions, respectively, while the grain boundaries showed an additional n-type electronic contribution under reducing conditions. Transmission electron microscopy revealed enrichment of Y in the grain boundary region. These findings indicate the existence of space–charge layers in the grain boundaries. A grain boundary core–space–charge layer model is therefore applied to interpret the data. Using a Mott–Schottky approximation, a Schottky barrier height of 0.5–0.6 V and an effective grain boundary width of 8–10 nm (= 2× space–charge layer thickness) is obtained at 250 °C in wet oxygen. Finite-element modelling of the complex impedance over a grain boundary with a space–charge layer depletion of protons yields a distorted semicircle as observed in the impedance spectra.

Photoelectron spectroscopy study of systematically varied doping concentrations in an organic semiconductor layer using a molecular p-dopant

We investigate the doping behavior of the strongly electron accepting molecule 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane coevaporated with the host molecule N,N,N′,N′-tetrakis(4-methoxyphenyl)-benzidine by photoemission spectroscopy and conductivity measurements. Using interface resolved measurements, we compare the alignment on different substrates and investigate the effects of varying doping concentrations on the Fermi level position. We find that at high doping concentrations the Fermi level gets pinned at the exponentially decaying tail of the highest occupied molecular orbital and compare these results with different dopants and host molecules. The measurement of the doping dependent space charge layer thickness yields information on the amount of free charge carriers and thereby the efficiency of the doping.

Mott-Schottky Analysis of Passive Films on Zinc by Electrochemical Impedance Spectroscopy under Potential Control

Generally, Mott-Schottky analysis on semiconducting materials is carried out by measurement of the impedance at different applied potentials using a single frequency. Thus, a simple capacity model is underlying the data evaluation and only one physical process for the sample is assumed to determine the measured impedance, e.g. variation of space charge layer thickness with potential. Electrochemically active materials exhibit a more complicated behaviour and other processes might influence the impedance at the chosen frequency. Therefore, measurement of the impedance spectrum in a wide range of frequencies would be desirable. Unfortunately, impedance data might also contain errors and artifacts originating from bandwidth restrictions of the potentiostat or cross talk between electrodes in a 3-electrode configuration. In this work, we present accurate electrochemical impedance measurements on zinc oxide passive films in the frequency range from 10-3 Hz to 106 Hz with simultaneous potential control.

Properties of ZrO2 Passive Film Formed onto Zr Electrode in 1 M NaOH at Low Voltage

In this paper, results of the potentiodynamic–potentiostatic formation of a homogeneous, passive film of on a Zr electrode in a 1 M NaOH solution at potentials lower than 4.0 V vs saturated calomel electrode are presented. The properties of such a film were investigated by electrochemical impedance spectroscopy (EIS) measurements. After fitting the EIS results by an appropriate equivalent circuit, the capacitance and resistance , as well as the space charge capacitance and space charge resistance of this film, were determined. The film was found to become an insulator (IN) at the potentials equal to and/or more positive than 2.0 V. In the potential range , a transition from a semiconducting to insulating behavior (SC-IN) has been recorded. The donor densities , as well as their flatband potentials and their space charge layer thickness, were determined from the corresponding Mott–Schottky plots recorded in two potential ranges and , where the film behaved as an n-type semiconductor. From the potential range of the insulating behavior of the film (IN), its thickness was determined from .

Micromachined sol–gel carbon nanotube/SnO2 nanocomposite hydrogen sensor

A novel micromachined single wall carbon nanotube (SWCNT) reinforced nanocrystalline tin dioxide gas sensor has been developed. The presence of SWCNT in SnO 2 matrix was realized by a spin-on sol–gel process. The SWCNT/SnO 2 sensor's sensitivity for hydrogen detection has greatly increased by a factor of three, in comparison to that of pure SnO 2 sensor. The novel sensor also lowers the working temperature, response time and recovery time. The greatly improved performances are mainly attributed to the effective gas accessing nano passes through SWCNT plus the smaller distance between adjacent gas accessing boundaries formed by the distribution of tiny SWCNTs. Therefore, both the spatial requirement ( D ≤ 2 L , D is the distance between adjacent gas accessing boundaries and L is the space charge layer thickness) and surficial requirement (adequate gas activation area) are met and the maximum inherent sensitivity of SnO 2 is achieved.

Characteristics of tunneling and impact ionization in ZnS:Mn-based thin-film electroluminescent structures

A method for measuring the characteristics of tunneling and impact ionization in thin-film electroluminescent emitters is suggested. This method makes it possible to find time dependences of the space-charge layer thickness near the anode and the length of the impact ionization region, to determine more exactly the time dependence of the field in the potential barrier at the cathode interface, the maximum depth of the surface states from which electron tunneling occurs, the minimum thickness of the barrier, and the electron tunneling probability, as well as the impact ionization rate for the deep centers related to structural defects of the phosphor layer.

Determination of free carrier density and space charge layer variation in nanocrystalline In3+ doped tin oxides using Fourier transforminfrared spectroscopy

A correlation between the surface reactions and the electrical response of doped nano-metal-oxide-semiconductors exposed to reducing gas is established using Fourier transform infrared (FTIR) spectroscopy. The effect of processing temperature on the microstructure evolution and the electronic conduction of the nanocrystalline In–SnO2 is presented. Variation in the charge carrier density is correlated to the solid/gas reaction of In–SnO2 in the nanodomain using the Drude-Zener theory including Spitzer and Fan’s [Phys. Rev. 99, 1893 (1955)] correction to accommodate for the quantum effects. Higher gas sensitivity for nanocrystalline size less than twice the space charge layer thickness is observed using in situ FTIR.

Growth, structure and electrical properties of tungsten oxide nanorods

Tungsten trioxide has shown good sensing properties towards various gases. Recently thin nanostructured WO 3 films have been tested. Due to their large surface area to volume ratio they exhibit good sensitivity depending on the grain size. However in conventional WO 3 thin films the average grain size exceeds the thickness of the surface space charge layer, so the electrical conduction is mainly controlled by the carriers transport across the grain boundaries. An alternative way seems to be in a monocrystalline material with nanometric dimensions. Our objective is to fabricate nanosized tungsten oxide rods and to test their sensing properties under gas adsorption. In this work, we focus on the growth, the structure and the electrical properties of tungsten nanorods. The tungsten oxide nanorods were grown by vapour transport from a WO 3 layer onto a substrate (Mica). The nanorods growth was controlled by the temperature gradient between the WO 3 layer and the substrate. Their morphology was investigated by AFM and their structure by TED and TEM. We have investigated the conductivity of the WO 3 nanorods with a technique derived from Atomic Force Microscopy operating in contact mode with a conductive tip (Resiscope).

New Interpretation of the Effect of Hydrogen on the Ion Distributions and Structure of Passive Films on Microalloyed Steel

It has been reported that hydrogen decreases the stability of the passive films on iron and stainless steel and promotes their localized corrosion. However, the mechanism of hydrogen-promoted corrosion is still not clear. Potentiostatic, electrical impedance spectroscopy measurements, and Mott-Schottky analysis were used to investigate the effect of hydrogen on the properties of the passive film on X70 microalloyed steel. In the range of passive potentials, hydrogen retards the passive film formation and decreases its stability. Impedance spectra of passive film on X70 steel show that hydrogen decreases the resistance towards charge transfer and ion diffusion and increases the capacitance of the passive film. Mott-Schottky analyses show that hydrogen increases the capacitance and donor density, and decreases the flatband potential and the space-charge layer thickness of the passive film. A new explanation is proposed for the effects of hydrogen on the properties of the passive films. According to this explanation, hydrogen creates an additional electric repulsion on or and oxygen vacancies, and enhances the diffusion rate of cations and anion vacancies. At steady state, hydrogen will not only decrease the concentrations of and but also increase the concentration of in the passive films, resulting in changes in the structure and a decrease in the thickness of the passive films. © 2004 The Electrochemical Society. All rights reserved.

A study of semiconducting properties of hydrogen containing passive films

Mott–Schottky and photoelectrochemical measurements were used to explore the effects of hydrogen and chloride ions on the electronic properties of the passive film on X70 micro-alloyed steel in a solution of 0.5 M NaHCO 3. Mott–Schottky analyses have shown that hydrogen increases the capacitance and donor density, and decreases the flat band potential and the space charge layer thickness of the passive film. The photocurrent of the film is remarkably increased by hydrogen. The effects of hydrogen become more pronounced with an increase in the hydrogen charging current densities. Hydrogen has no noticeable effect on the band gap energy E g and the process by which hole-electron pairs are photo-generated in the film. The presence of chloride ions in the solution produces some similar effects on the electronic properties of the passive film to those observed with hydrogen, but reduces the photocurrent and increases the band gap energy of the film. No significant synergistic effects on the electronic properties of the passive film were observed in the presence of hydrogen and Cl −. These results provide very useful information for elucidating the mechanism by which hydrogen changes the properties of passive film and then promotes localized corrosion.

Grain boundary segregation in yttrium-doped polycrystalline TiO 2

Grain boundary segregation of yttrium in titanium dioxide is studied systematically as a function of dopant concentration. Local grain boundary defect chemistry is quantitatively determined by analytical transmission electron microscopy and compared to equilibrium space-charge segregation models that incorporate both the electrostatic and elastic strain-energy driving forces for solute segregation. The thermodynamic models show that the elastic strain-energy driving force dominates in this system and that the electrostatic driving force contributes a 10–20% correction to the total solute segregation. In comparison to the experimental results, the theoretical models provide good predictions for several grain boundary parameters including local stoichiometry, solute interfacial excess and space-charge layer thickness.

A physical model of anode spot formation in a high-current vacuum arc

Physical and mathematical models are suggested for the description of anode heating and anode spot formation. An increase in the vacuum discharge current is accompanied by the crisis of cathode ion flow which leads, at a certain (critical) value of current, to the impossibility for the ions to reach the anode. It is known that, in this case, a layer of negative space charge with positive anode drop is formed, as well as an electron beam. The magnitude of anode drop depends on the thickness of the space charge layer and on the form of the electric circuit. A nonlinear dependence of the space charge layer thickness on the discharge current density is obtained. The presence of such a dependence makes it possible to solve the electric circuit in view of nonlinear unsteady-state resistance and capacitance of the layer and to calculate the voltage across the layer, the current density and the power density on the anode, as well as to calculate the anode surface temperature. The results of calculations of the time required for anode spot formation and of the time dependence of voltage across the space charge layer agree with the experimental data.

Analysis on the Passive Films of Fe, Cr and Fe-25Cr Alloy by Photo-Electrochemical Methods

Passive films on Fe, Cr and Fe-25Cr formed in pH 8.5 buffer solution at potentials 0 to 900 mV vs. SCE were examined by photo-electrochemical methods that use monochromatic light source generated by Xe lamp with a scanning digital monochromator automatically controlled by a stepping motor. The passive film formed on Fe was structurally similar to γ-Fe 2 O 3 . Band gap energy for the passive film exhibiting an amorphous semi-conductor was newly interpreted by considering the contribution of localized states to the photo current. Photo current spectra of passive films on Fe were analyzed in terms of γ-Fe 2 O 3 with a spinel structure. The p-d and d-d excitation processes were involved in the photo current spectra of passive film on Fe. The structure of the passive film formed on Fe and Fe-25Cr alloy were discussed by comparing the influences of passivation potential on the band gaps measured at the same potential. Effects of addition of Cr to Fe on the electronic structure of the passive film were studied by comparing the photo current spectra and band gaps for the passive film on Fe-25Cr with those on Fe and Cr. A significant reduction in the photo current for passive film on Fe-25Cr compared with that on Fe was associated with a decrease in the space charge layer thickness by an increase in the density of the localized energy state.

Kinetic Study of Lithium Electroinsertion in Titanium Oxide Thin Films

The electrochromic reaction of titanium oxide films prepared by RF sputtering was studied. Chronopotentiometric experiments associated with transmittance measurements in LiClO[sub 4]/propylene carbonate solutions were carried out for several film thicknesses. The reaction kinetics is controlled by lithium ion diffusion into the titanium oxide matrix. The diffusion equations have been solved for the appropriate finite boundary conditions, and from these analyses l[sup 2]/D values are obtained. Combining these data with coulometric titration data, one can conclude that the diffusion phenomenon is only produced in a part of the film. The l parameter was calculated and a value of 11 nm was obtained, coinciding with the thickness of the accumulation space charge layer for n-type TiO[sub 2]. Consequently, Li[sup +] diffusion process only occurs in this region. 20 refs., 10 figs., 1 tab.

ChemInform Abstract: Experimental Techniques for the Study of the Semiconductor‐Electrolyte Interface

AbstractReview: (137 refs.

GaAs Schottky Diode's Lateral Surface Potential Distribution

A high resolution scanning Auger microprobe was used to determine the potential on the surface as a function of the lateral distance from the Schottky electrode edge. The voltage varies nearly linearly with distance. For a hard breakdown case, the surface field is ∼1.2E5 V/cm, similar to that in a computer simulated JTE case with bound charges ∼1.2E12 cm−2 extending laterally to twice the space charge layer thickness. For a leaky junction, the surface field is in 1E4 V/cm range, with small variations as a function of the current, similar to a SIPOS case.