Passivation Kinetics Research Articles

Numerical simulation of creation-passivation kinetics of interface traps in irradiated n-channel power VDMOSFETs during thermal annealing with various gate biases

Influence of gate bias on creation-passivation processes of interface traps in irradiated n-channel MOS transistors during thermal annealing has been investigated. The experimental results, which show the dependence of these processes on gate bias, are explained by combined hydrogen-water (H-W) model. The modelling of kinetics of creation and passivation of interface traps, based on bimolecular theory and numerical analysis, is also performed. Numerical simulation shows that H-W model predicts the maximum of interface trap density and latent interface trap buildup during thermal annealing.

Modelling of kinetics of creation and passivation of interface traps in metal-oxide-semiconductor transistors during postirradiation annealing

The dependencies of creation–passivation processes of interface traps in irradiated n-channel metal-oxide-semiconductor transistors on the temperature and gate bias during annealing have been investigated. The experimental results, which are explained by the hydrogen–water (H–W) model, show the influence of both the annealing temperature and gate bias on these processes. The modelling of creation–passivation kinetics of interface traps, based on bimolecular theory and numerical analysis, is also performed. Numerical modelling shows that the H–W model can include the temperature and gate bias dependencies of creation of interface traps, latent interface trap buildup and the decrease of interface trap density.

Passivation kinetics of surface films formed on a graphite electrode in organic lithium salt solution as a function of salt anion type

The passivation kinetics of a graphite electrode have been investigated as functions of applied potential and salt anion type by using cyclic voltammetry and current transient experiments supplemented with ac-impedance spectroscopy. The cyclic voltammogram and current transient were obtained after abrading the graphite bulk electrode subjected to various negative potentials with respect to the open circuit potential of about 3.0 V (Li|Li+) in 1 M LiAsF6, LiPF6 and LiN(SO2CF3)2+ ethylene carbonate (EC) + diethyl carbo (DEC) solutions. The current transients illustrated the passivation kinetics which can be split into two steps of prepassivation and passivation. The LiAsF6 salt gave a reduced reduction current in the second cycle of the voltammogram, the steeper slope of the current transient and the lowered ratios of Rporous to Rcompact and of Ccompact to Cporous obtained from the measured impedance spectra as compared to LiPF6 and LiN(SO2CF3)2 salts. The three factors are characterized by the improved passivity of the surface film formed in LiAsF6 + EC + DEC solution. The passivity of the surface film on the graphite electrode has been discussed in terms of the reactivity of the salt anion towards reduction at the electrode.

Comparative analysis of the H 2 passivation of interface defects at the [formula omitted] interface using electron spin resonance

The passivation with molecular hydrogen in the range 213–234°C of the interfacial P b0 and P b1 defects in (100) Si SiO 2 , thermally grown at low temperature (<750°C), has been analyzed by K-band electron spin resonance. The passivation kinetics are found to be well described by the same defect-H 2 reaction limited model applying to the interfacial P b defect (∘SiSi 3) in (111) Si SiO 2 grown at 850°C. However, unlike P b , that was typified by a single-valued activation energy for passivation E a = 1.66 eV, both P b0 and P b1 are found to exhibit a Gaussian spread σ Ea ∼ 0.15 eV around their respective mean E a values, deduced as 1.51 and 1.57 ± 0.3 eV. The similar passivation kinetics are in line with assigning the P b0 and P b1 defects, like P b , to an interfacial unpaired sp 3 Si hybrid. However, as there is no fundamental difference between P b0 and P b1 regarding passivation in H 2, more specfic identification of P b with either P b0 or P b1 , if any, cannot be concluded.

Electrochemical and surface studies of the passive layers grown on sputter-deposited nitrogen-stainless steel alloys in 1M H 2SO 4 solution

The passive behavior of nitrogen-free (N-free) and nitrogen-bearing (N-bearing) stainless steel sputtered coatings was studied in a 1M sulphuric acid solution. The influence of nitrogen on the passivation parameters was investigated with respect to metallurgical features. Potentiodynamic measurements show two types of passivation kinetics for coatings containing a nitrogen content > 13 at% N. This electrochemical behavior affects the steady-state of passive film with respect to the coating grain size and the polarization applied. X-ray photo-electron spectrometry (XPS) analyses were used to understand the compositional changes that seem to be induced by chemical dissolution.

Composite gel electrolyte for rechargeable lithium batteries

Composite polymer electrolyte films consisting of zeolite powders dispersed in poly(acrylonitrile) (PAN)-based gels with LiAsF 6 have been prepared and their electrochemical properties studied. Gel electrolytes prepared by adding LiAsF 6 in propylene carbonate (PC) and ethylene carbonate (EC) mixtures with PAN have demonstrated ionic conductivities greater than 10 −3 S/cm at room temperature and above. The addition of zeolite powders increased ionic conductivity at low temperatures due to the highly amorphous nature of the composite film. Impedance spectroscopy was performed to study the Li electrode/electrolyte interface and a reduction of the passivation kinetics was observed. Cyclic voltammetry showed that addition of PAN and zeolite powder to LiAsF 6, PC and EC mixtures did not change the stable electrochemical potential window. In Li LiCoO 2 cells, at 25 °C, these composite electrolytes demonstrated current densities as high as 0.5 mA/cm 2, with little voltage or capacity loss compared with cells with liquid electrolytes.

Kinetics of copper passivation and pitting corrosion in Na 2SO 4 containing dilute NaOH aqueous solution

The electrochemicala behaviour of Cu in alkaline solutions containing Na 2SO 4 was studied using potentiodynamic and potentiostatic techniques complemented by scanning electron microscopy. The presence of Na 2SO 4 enhances Cu electrodissolution through the passive layer and decreases the breakdown potential. There is a critical OH -/sulphate concentration ratio for the onset of localized corrosion. The competitive interaction between OH - and sulphate ions at the passive layer can explain the experimental data. Pit initiation fits the point defect model for passivity breakdown. Pit growth involves a number of current contributions which can be distinguished through the analysis of current transients at constant potential by using nucleation and growth models.

DEFECT METASTABILITY IN HYDROGEN PASSIVATED POLYCRYSTALLINE SILICON

A comprehensive review is presented for the defect passivation and the light-induced metastability in fine grain polycrystalline silicon (poly-Si). The passivation kinetics of grain boundary defects were examined by electron spin resonance and secondary ion mass spectrometry measurements. The spin density decreases to a residual value which strongly depends on the passivation temperature and a further low-temperature anneal reduces the spin density to N S =2.2×1016 cm −3. Illumination with white light produces additional dangling bond defects which are metastable and can be removed by an anneal at moderate temperatures. The light-induced degradation decreases with repeated illumination and annealing cycles and is restored upon re-exposure to monatomic H. Our results provide the strongest evidence to date that hydrogen is responsible for the metastability in both poly-Si:H and hydrogenated amorphous silicon.

Influence of near-surface microstructures on the transient current response in Fe-Cr-Ni alloys during scratch tests

Metals and alloys are protected from the corrosive environments in which they are used by the presence of a passive film on the surface. However, the passivity of a metal surface cannot be preserved if mechanical forces rupture this protective film from the surface. Thus, during corrosive wear, the process of wear essentially destroys the passive film, which then leaves a bare metal surface for the corrosion reaction to start taking place once again. In an industrial application of a metal, the process of passivation, depassivation, and repassivation kinetics must be completely understood if the life of a metal part is to be prolonged. The purpose of this article is to study the kinetics involved in the corrosive wear of Fe-Cr-Ni alloys by the scratch technique and to determine the relationship between the electrochemical response of these alloys and the near-surface microstructures.

Passivation and repassivation kinetics of iron-aluminum alloys in 1 N H 2SO 4 using potential step and scratch tests

Experiments were conducted by US Bureau of Mines researchers with iron-aluminum alloys (5–25wt.%Al) in 1 N H 2SO 4 to determine the amount of charge required to repassivate their surfaces following scratching with a diamond indenter, to gain a better understanding of how wear and corrosion interact. This understanding is aimed at reducing the corrosion and wear of materials. Solutions saturated with air were used at ambient temperature. Formation of the passive films was studied by measuring the current transient resulting from stepping from the open circuit corrosion potential to the passive region of +1.175 V(NHE). The repassivation kinetics were studied by measuring the current transient caused by scratching a rotating disc electrode with a diamond indenter while holding at the passivation potential. Comparison of the charge density required to form or repair the passive film was made for the potential step and scratching experiments. The amount of charge required to repassivate the film was determined as a function of indenter load, shape, velocity and aluminum content.

The effect of indenter shape on the transient current response and surface microstructures in Fe-16wt.% Cr-16wt.%Ni alloy

The effect of indenter shape on the transient current response of Fe-16 wt.%Cr-16 wt.%Ni alloy has been investigated in an 0.01 M H 2SO 4-0.01 M KCl electrolyte. Various Rockwell hardness indenters with C-Brale, Vickers, 1 16 in and 1 8 in balls at their tips have been used in this study to produce scratches of different shapes on the alloy when the specimen was being rotated at 1500 rev min −1 in the given electrolyte. The transient current increases linearly with increasing impact force of the stylus. The transient current response in itself indicates various stages corresponding to passivation, depassivation and repassivation kinetics of the samples. The details of the kinetics have been discussed in this paper. The scanning electron micrographs indicate that the area of the scratches increased with increasing applied load, and the morphologies of the scratches appear to be quite different in air and electrolyte. The scratches are usually more elongated in the electrolyte.

Kinetics of Dopant Metastability in a-Si:H

ABSTRACTSmall temperature-induced perturbations from thermodynamic equilibrium of doped hydrogenated amorphous silicon (a-Si:H) are explored by dark conductivity measurements. The equilibration kinetics reveal significant differences between phosphorus and boron doping. Raising the temperature leads to an increase of electron/hole densities which are related to the activation of additional dopants, while a decrease of temperature causes the opposite effect of dopant passivation. The creation kinetics of P doped a-Si:H is stretched exponential with a temperature independent β value of 0.85 whereas dopant passivation in the same temperature range is also stretched exponential decay, but with values for β &lt; 0.8. In contrast, the kinetics of boron activation and passivation are stretched exponential with equal β values. The time constant τ to achieve thermodynamic equilibrium for both activation and passivation is thermally activated with energies ≃ 1.1 eV for P and B doped a-Si:H. τ depends weakly on the degree of perturbation. A discussion and interpretation of the data based on hydrogen migration in a-Si:H is given.

Hydrogen Passivation and Reactivation of DX Centers in Se-Doped and Si-Doped AlGaAs - - A Comparison

ABSTRACTThe effect of hydrogenation on DX centers was evaluated for both Si- and Se-doped AlxGa1-xAs (x=0.26 and 0.23). MBE-grown AIGaAs:Si and MOCVD-grown AIGaAs:Se epilayers were hydrogenated with either monatomic hydrogen or deuterium from a remote plasma at 250°C for 1h. The passivation and subsequent reactivation kinetics were studied with C-V and DLTS techniques. Reactivation was investigated in the space-charge layer of Schottky diodes under different bias conditions. While the Group VI and Group IV deep donors respond similarly to passivation, they display significantly different reactivation kinetics, with thermal dissociation energies of 1.5 eV and 1.2 eV for Se-H and Si-H, respectively. These values are close to the energies previously determined for reactivation of the Si and Se shallow donors in both AIGaAs and GaAs. Therefore, they are not significantly dependent on the Al concentration (x &lt; 0.30) even for donors residing on the As sublattice. Our results are consistent with the Chang-Chadi model of DX centers.

Interaction of H and H2 with the silicon dangling orbital at the Si/SiO2 interface.

We present a molecular-orbital study of trivalent silicon atoms on the 〈111〉 Si/${\mathrm{SiO}}_{2}$ interface in the presence of atomic and molecular hydrogen. We consider both passivation and depassivation of dangling silicon orbitals as a function of charge state. Our results for the neutral charge state are in good agreement with experiment. We predict a 1.32 eV activation energy for the concerted reaction involving ${\mathrm{H}}_{2}$ dissociation and Si-H bond formation, compared with Brower's experimental value of 1.66 eV, and we predict a Si-H detachment energy of 2.7 eV, compared with 2.5 eV obtained by Brower and Myers. We predict that biased annealing would lead to strikingly different passivation kinetics.

Photoelectrochemical Characterization of the Anodic Film on Zinc in KOH Solution

The passive film on a zinc electrode is often assumed to be composed of . Since removal of the electrode from the solution could alter the film composition, an in situ measurement technique is required for a qualitative analysis. We have developed a model to simulate the kinetics of anodic dissolution and passivation on the zinc electrode in alkaline electrolyte. In our model is postulated to be responsible for the passivation of the electrode. To check this hypothesis we performed photocurrent measurements and we compared the results with those obtained on bulk material. Based on the differences in photospectra as a function of electrode potential, we infer that the surface composition changes with potential. Although photospectra from the passivated electrodes are not identical to those from bulk material, key characteristics closely correspond.

Passivation kinetics of two types of defects in polysilicon TFT by plasma hydrogenation

The effects and kinetics of hydrogen passivation on polycrystalline-silicon thin-film transistors (poly-TFTs) are investigated. Based on the response of device parameters with the progress of hydrogenation, two types of defects can be distinguished from the difference in passivation rate. The threshold voltage and subthreshold slope, which are strongly influenced by the density of dangling bond midgap states, have a faster response to hydrogenation. The off-state leakage current and field-effect mobility, related to stain-bond tail states, respond more slowly to hydrogenation, with an onset period of approximately 4 to 12 h depending on the grain size. Since the larger-grain-size samples showed a longer onset period, the contribution of intragranular defects to the strain-bond tail states appears to be significant.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Kinetics of Passivation of Stainless Steels in Chloride Solutions

Kinetics of Passivation of Stainless Steels in Chloride Solutions

Study of the Passivation Kinetics of Zircaloy 4 in Chloride Containing Aqueous and Hydroorganic Solutions

Study of the Passivation Kinetics of Zircaloy 4 in Chloride Containing Aqueous and Hydroorganic Solutions

ChemInform Abstract: Kinetics of Passivation of Lead in Phosphate Solutions

Abstractare studied as a function of pH and phosphate concentration by means of potentiometric and impedance measurements.

Kinetics of passivation of lead in phosphate solutions

A kinetic study on passivation of lead in phosphate media was made by potential and impedance measurements. In pH's > 2.01, the potential gets nobler with time, indicating passivation of the lead electrode. This was confirmed from measurements of the relative change in the thickness of the passive layer which was found to increase with time following a direct logarithmic law. The magnitude of the rate of growth of the layer as well as the discontinuity in this rate were correlated with the mechanism of film growth. Layers grown in the pH range 2.01–4.60 are adherent and thin, whereas those formed in pH's >4.6 are thicker and porous.