Pit Formation Process Research Articles

Comparison of reliability of 100 nm AlGaN/GaN HEMTs with T-gate and SAG-gate technology

The effect of gate technology and semiconductor passivation on the switching speed and device reliability has been investigated. By reducing the parasitic capacitances and reducing the passivation induced surface charge density a median lifetime of around 106 h at a channel temperature of 125 °C and a current-gain cut-off frequency of 74 GHz for a T-gate technology has been achieved. By electroluminescence and TEM cross-sectioning of a stressed device a local inhomogeneous pit formation process was found as the major degradation mechanism for the decrease of the saturation current.

Multi-state Markov modeling of pitting corrosion in stainless steel exposed to chloride-containing environment

Although stainless steels (SSs) have excellent general corrosion resistance, they are nevertheless susceptible to pitting corrosion. The variation of pit depth and density is significant for the prediction of likelihood of corrosion damage occurring in service. Among the available pitting corrosion models, it is difficult to identify a specific model capable of characterizing all the pit formation processes observed and one that can be used for estimating the evolution of pit density distribution with time. A physics-based multi-state Markov model giving a full description of pitting corrosion states is presented. The transition rates used in the model are determined by fitting the model to experimental data. The variation of pit depth and density is simulated. The simulation is verified by experimental scenarios of SS exposed to chloride-containing environments.

Anodic Behavior of Aluminum in Glycine Aqueous Solutions at Various pH Values

At the present work, it was investigated aluminum (Al 99.99%) anodic behavior in glycine aqueous solutions (in the concentration range from 10–4 to 10–1M) at various pH values (pH 4.8 - 8.4). Reliability of the obtained experimental results was confirmed by use of a complex of independent physic-chemical methods (voltammetry, chronoamperometry, optical microscopy (МBS-2 (x7) and МIМ-7 (x500)), scanning electronic microscopy (SEM, x1000) with JEOL-6380LV and energy-dispersive X-ray analysis (EDXA) with INCA Energy-250).The received data have shown that depending on the pH, the amino acid exhibits a dual effect. On the one hand, glycine zwitter-ions (pH 4.8–5.8) conducts one’s self like an inhibitor slowing down the anodic process and aluminum is in a stable passive state at these pH values in the vicinity of the isoelectric point of the investigated amino acid. Under this the probable reason of the observed effect consists of strong intermolecular hydrogen bridges which are formed between the amino and carboxy groups in the amino acid zwitter-ions predominate over it’s interactions with the oxidized aluminum surface. It follows from this that glycine zwitter-ions do not participate in the anodic process on aluminum, and the passive film on aluminum surface is formed upon metal–water interaction according to the following scheme because of a high chemical affinity of aluminum to oxygen:Al + yH2O → [Al (H2O)y]ads (1)On the other hand, it has been shown that the glycine anions formed at pH = 8.4 stimulate pit formation (PF) on oxidazed aluminum surface in these solutions (pit depth was 6 μm at 10-1 M). The choice of this pH value was caused by two reasons. In the first place, at pH = 8.4 the system contains both inactive zwitter-ions and active glycine anions. Secondly, solutions with higher pH might cause intense general corrosion of aluminum. The data about aluminum anodic behavior in glycine solutions (pH = 8.4) were analyzed on the basis of the nucleophilic substitution theory, according to which PF observed on aluminum involves nucleophilic substitution of ligands of adsorbed surface complexes by corrosive solution components with subsequent hydrolysis of a compound formed. Generalization of experimental data and literature data [1-3] allowed us to suggest the following multistage mechanism of the PF process:Al + yOH- = [Al(OH)y]z1-y ads + z1e- (2) [Al(OH)y]z1-yads → [Al(OH)y-k]z1´-y ads + k OH- (3)[Al(OH)y-k]z1´-y ads + Gly- = [Al(OH)y-kGly]z2-y ads (4)[Al(OH)y-kGly]z2-y ads = Alz3 + Gly- + (y – k) OH- + (z2-z3)e- (5)According to the kinetic analysis data obtained in the present investigation, the limiting stage of the PF process studied is dissociation of the initial complex at equation (3).This fact is confirmed by independence of the PF process rate from activator –glycine anions. ReferencesT.A. Borisenkova, S.A. Kaluzhina // Int. J. Corros. Scale Inhib., 2, 122 (2013)T.A. Borisenkova, S.A. Kaluzhina // Condensed matter and interphases, 13, 136 (2011).T.A. Borisenkova, S.A. Kaluzhina // ECS of the 218th Meeting, Las Vegas, №1227 (2010).

Novel growth mode of solid–liquid–solid (SLS) silica nanowires

Abstract

Three-dimensional Macropore Arrays in $p$-type Silicon Fabricated by Electrochemical Etching

Ordered macropores formed in p-type silicon substrates (10 ∼ 20 Ω·cm) by using electrochemical anodization in various HF-containing electrolytes was investigated under different operating conditions. The effect of electrolyte composition and etch pits on controlling the formation of macropores on periodically arranged pores is reported. The results revealed that the natures of the constituents of the solution play very important roles in determining pore formation and morphology and that stable ordered macropore growth is not possible without an inverse pyramid notch. By using a Si/SiGe/Si/SiGe/p-type silicon structure, we were able to fabricate ordered pillar structures without an etch pit formation process. A possible role of two sets of Si/SiGe layers in pillar formation is proposed.

Macropore Formation in p-type Silicon and Si/SiGe/Si/SiGe/p-type Silicon

Random and ordered macropore formation in p-type silicon substrate (10 ~ 20 ohm•cm) by electrochemical anodization in various HF-containing electrolytes was investigated under different operating conditions. The effect of electrolyte composition controlling the macropore formation both for random and periodically arranged pores is reported. The role played by etch pit for ordered macropore formation was investigated. The results revealed that the nature of constituents of solution plays very important roles in determining pore formation and morphology and the stable ordered macropore growth is not possible without etch pit. By using Si/SiGe/Si/SiGe/p-type silicon structure, ordered pillar structures were fabricated without etch pit formation process. The possible role of two sets of Si/SiGe layer for pillar formation is proposed.

Digital Image Analysis of Etch Pit Formation in CR-39 Track Detector

An in-situ observation system was developed to record time-lapse images of etch pits formed on the surface of a solid-state nuclear track detector (SSNTD), CR-39. The CR-39 track detector was irradiated with alpha and Li particles produced by a neutron capture reaction, 10B(n,α)7Li. The time-lapse images of the etched surface of the detector were carefully observed to elucidate the etch pit formation process. Pit-evolution images were constructed by digital image processing of the data of the time-lapse images. In addition, a finite element model of SSNTD was used to simulate the etch pit formation. Pit-evolution image analysis and computational simulation were performed to reveal the etch pit formation obtained via the incidence angle of energetic particles on a CR-39.

Characterization of pitting corrosion in bare and sol–gel coated aluminum 2024-T3 alloy

The prevention of pitting corrosion in aerospace aluminum alloys by the application of protective sol–gel coatings requires a thorough understanding of pit formation kinetics and morphology developments in such surface coating systems. This study reports results of chemical and electrochemical methods of pitting corrosion tests for bare and sol–gel coated Al 2024-T3 alloy. Specific attention is focused on the characterization of pitting in samples coated with vinyl-silicate and epoxy-silicate sol–gel coatings. Specimens were exposed to a variety of chemically aggressive environments, based on 3–5% NaCl solutions with addition of HCl and H 2SO 4, including a standard CASS solution. The exposure of bare samples to these environments produced extensive surface corrosion, but pits were not observed for sol–gel coated samples. Anodic polarization tests with potentials above that required for pitting in bare samples were used to initiate pitting corrosion in sol–gel coated samples. A corrosion current monitoring test provided a method of controlling the pit formation process, which provides well-defined pits in terms of spatial density and geometry. A two-stage kinetic phase in pit development was observed and correlated with pit morphological developments in sol–gel coatings. An initial low current stage was associated with pit penetration through the coating to the surface and the secondary high current stage was associated with an active growth stage which grew in sub-coating surface interface regions. Results of this research provide a basis for designing and improving corrosion protection systems based on the application of sol–gel coatings.

Morphological pattern formation in pitting corrosion

From the point of view that pitting dissolution is induced by nonequilibrium fluctuations, pattern formation on pitting surface is examined. Accompanied with repeated destruction and reformation of passive film, the metal surface fluctuates by the thermal motion of solution particles, and the possibility of pit formation may be realised. The pit formation process is summarized as follows: the electrode system first selects the components with appropriate wave numbers from the thermal fluctuations, and then makes them larger with time. These fluctuations can be assorted into two types, i.e., asymmetrical and symmetrical ones; the former decides the overall pit pattern and the latter minute irregularities inside the pit. Then, the intrinsic spatial power spectrum plays the important role which determines the asymmetrical fluctuations. Consequently, it is clarified that the overall pit patterns are decided not by the surface physical parameters like the surface energy, but by the parameters affecting the instability and autocorrelation distance of the fluctuations such as the Cl− ionic concentration and overpotential.

Modeling delamination due to thermal stress in optical storage media

Finite element analysis is used to calculate the shape of blisters formed in bilayer optical storage media due to the buildup of thermal stresses during laser writing. It is shown that practically usable blisters may be expected to form in a time period of about 15 ns. Such a thermal stress delamination process may also precede melting in conventional pit formation processes.

A study of laser marking of thin films

Some observations of laser marking of thin films are presented. Time-resolved reflectivity measurements performed during laser marking of thin organic films indicate that the pit-formation processes start in less than 10 ns after the onset of the laser pulse and that some reversal of the process occurs following exposure termination. Temperature calculations for laser heating of thin films with focused scanning beams explain some of the mark (pit) morphology and material flow behavior that is observed. Scanning electron microscopy (SEM) studies of the marks indicate that at high laser powers, pit formation occurs by ablation and at low laser powers, pits can be formed without ablation. Pits were also formed in a 100nm thin film by resistive heating where the maximum temperature was less than 300 °C.

Thermal stress mechanisms in optical storage thin films

Numerical calculations are presented that show that thermal stresses induced by laser heating in optical storage media may reach the failure strength of the materials used during the early stages of a laser pulse. It is shown how these stresses arise and how the failure process may then proceed by a combination of radial compressive stresses and axial tensile stresses producing damage by elastic buckling and interface failure. The formation of a stable blister for optical storage purposes is then possible. Alternatively such effects may contribute to the initial stages of current pit formation processes. Such thermal stresses may also have long term detrimental effects, producing interface damage, in many other multilayer optical storage systems, particularly those with high thermal expansion coefficients.

A model for laser marking of thin organic data storage layers by short intense pulses

A mathematical model is developed to describe the pit formation process in thin (∼0.1 μm) organic layers induced by short (<100 ns), intense laser pulses. The basic premise is an ablation-driven viscous flow, in which the reactive pressure gradient due to polymer decomposition causes fluid motion. Contrary to the case of thick layers (∼1 μm) and long (∼500 ns), weak pulses, here surface tension gradients are shown to be too small to promote material flow in the short time span of laser exposure. The derived closed-form expressions for temperature profile and pit contour allow expedient calculation of threshold energies and prediction of functional relationships among imposed (e.g., pulse energy and width) and measured (e.g., pit width) system variables. Model predictions compare favorably with experimental observations of such interrelations.

In-Sio_2 cermet films for optical recording

In-SiCO(2) cermet films have been studied as optical recording media in metal film ablation memory. Specular surfaces and the minimum writing threshold laser power have been obtained in SiO(2) 40-60-vol.% composition. Pit formation processes have been studied by the temperature bias method, and the use of a trigger layer has been proposed for decreasing the writing laser power. Bi-Pb-Sn-In eutectic alloy and SiO(2) cermet film have also been examined. The 35-mJ/cm(2) writing threshold laser energy was obtained in this cermet and the phthalocyanine trigger layer construction. Cermet films are stable up to 500 degrees C and are also stable in water.