A computational mass transport framework for occluded region corrosion was extended to study alloys exposed to the thin electrolytes characteristic of atmospheric corrosion. Of interest were the interactions of an aluminum-clad layer with its Al-substrate in the vicinity of a scratch. The model focuses on open circuit conditions and local galvanic couples. Accurate electrochemical kinetics for metallic clad and bare AA2024-T3 are used, including the observed decrease in the pitting potential with increasing chloride concentration. The model has been applied to studies of the parameters that affect the throwing power of metallic claddings (e.g., scratch size, [Cl-], ipass, idl). Two geometries were investigated: a 1-D model and a square sample (two spatial dimensions) with a scribed cross, the latter simulating to what is usually done experimentally in exposure testing. A quantitative computation of the throwing power of metallic cladding on AA2024-T3 in thin electrolytes was achieved, including the effect of the criterion for scratch protection. For the base case of electrochemical behavior studied, a loss of protection ability was observed between a scratch size of 50 μm and 500 μm for the most conservative protection criterion (i.e., protection is achieved when the potential of all points in the scratch is at or below the pitting potential of the cladding). When a less conservative protection criterion is used, the size of the scratch that can be protected increased to between 500 μm and 3500 μm.

The metallic cladding modeling also demonstrated the equivalence of reducing the ipass of the clad or increasing the idl for oxygen reduction on the AA2024-T3 on the size of the scratch that can be protected. A less than linear dependence was found between these parameters and the scratch size that can be protected. An order of magnitude reduction in ipass (or increase in idl) led to a decrease of anywhere from 40% to 90% in the scratch size that was protected. Two competing effects of increasing the chloride concentration in the thin electrolyte were observed. Higher chloride concentrations increased the throwing power (due to increased conductivity), but they also lowered the pitting potential of both the cladding and the base material. In our simulations, the former dominated the latter, indicating better protection of scratches at higher chloride concentrations, with the extent of the effect depending on the protection criterion used.

Correlation between the susceptibility to breakdown and surface properties of thin films on implant titanium alloys Ti-5Al-4V and Ti-6Al-4Fe in Ringer 1 and Ringer 2 solutions of different pH values (6.98, 4.35, 2.5) which simulate the conditions that can appear at the longterm (13,000 hours) contact between implant and tissues were studied in this paper. The passive films are very stable up to +1.8 V; Ti-6Al-4Fe alloy presents pitting attack at a pitting initiation potential of +3.5 V in Ringer 1 solution and at +3.9 V in Ringer 2 solution. The pitting protection potential is about +1.75 V in both solutions; this is a very noble potential. Impedance spectra were modeled with one time constant equivalent electrical circuit, typically for a compact oxide film, for all materials, in all tested solutions. The fitting parameters indicate a long-term stability.

The paper presents the experimental results concerning the performance assessment of electrodeposited epoxy films using electrochemical techniques (electrochemical impedance spectroscopy–EIS and anodic polarization) assisted by microscopical studies. The films were formed during the cathodic and anodic electrodeposition of a modified epoxy resin on carbon steel substrate. The specimens were tested in a normal aerated 3% NaCl solution at room temperature for a total period up to 1500 hours. Analysis of the impedance spectra has established an equivalent electric circuit with two time constants fitted to describe the electrodeposited epoxy film/carbon steel/electrolyte system. The time monitoring of the principal elements from the equivalent electric circuit were used to determine protective properties of the electrodeposited epoxy films. Results show a high performance of electrodeposited epoxy films, characterized by uniformity, insignificant porosity, very low water and ions permeability.

We studied the initial stages of the electrodeposition of Pb in the presence of chlorine ions on Cu(100), using an oblique-incidence optical reflectivity difference (OIRD) technique. The OI-RD results reveal that immediately following the underpotential deposition (UPD) of the first Pb monolayer, two different types of bulk-phase films grow depending upon the magnitude of overpotential and cyclic voltammetry (CV) scan rate. At low overpotentials and/or slow scan rates, we propose that a bulk-phase Pb film grows on top of the UPD monolayer. At high overpotentials and/or fast scan rates, either a PbO, PbCl2, or a rough Pb bulk-phase layer grows on top of the UPD layer such that the reflectivity difference signal from such a film has an opposite sign.

Various metals with different galvanic potentials are used to fabricate the microelectronic circuits. One of the most commonly used processes during integrated circuit manufacturing is the tungsten via fill. To obtain maximum interconnect density with low via resistance requires that metal-via overlap is essentially zero. Zero overlap with litho variations and thus misalignment may result in unlanded vias. Since the vias are used to connect various metal levels, a large number of these cases may occur causing device failures and thus yield loss. To study this problem a variety of test structures were studied and a new mechanism of corrosion was found. The tungsten corrosion observed in these structures was found to be photo-induced. In this paper we will discuss the mechanism of photoinduced galvanic corrosion that occurs between the aluminum and tungsten metal layers during microelectronic manufacturing.

We describe the electrochemical deposition of molybdenum oxide thin films prepared from aqueous solutions containing peroxo-poly and oxometallate complexes of molybdenum(VI). Electrochemical quartz crystal microgravimetry (EQCM) was used to establish corresponding reaction mechanisms for films grown at different deposition potentials. Electrodeposition from acidified sodium molybdate solutions proceeds by the reduction of molybdic acid; whilst deposition from aqueous peroxo-based solutions involves the graded reduction of several solution components, primarily comprising molybdic acid and peroxopolymolybdates. Films grown from acidified sodium molybdate solutions are weakly adherent and easily rinsed off, while those grown from peroxo-polymolybdate solutions are strongly attached and stable. Careful regulation of the deposition potential allows for controlled growth of distinct molybdenum oxide compositions to produce films with varied water content and valency. Electrochemical deposition through sacrificial colloidal-crystal templates is also demonstrated to prepare macroporous thin films comprising hexagonally close-packed arrays of spherical pores.

The surface of a set of zinalco (Zn-22Al-2Cu) samples was prepared by mechanical polishing (MP) and by electropolishing (EP). Samples were subjected to environmental corrosion during 56 days and studied by x-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). Differences in relative atomic concentration ratio of Al/Zn in oxides of the surface layer were obtained and they are related to the bulk microstructure. A different corrosion behavior is observed between MP and EP samples and it is explained in terms of surface composition and morphology. The initial growth of corrosion products was observed in EP samples and a corrosion model is proposed. The surface of both types of samples can be modified by lowenergy argon ion bombardment.

A new Zn–Al-Ag alloy (ZINAG) with mechanical superplastic properties has been developed. In this work four of the Zn–22wt%Al eutectoid alloy doped with between 0.5 to 4.24 wt% Ag have been studied. The superplastic behavior can be explained as a consequence of the fine grain distribution induced during the deformation process. Here the corrosion resistance of these alloys was studied by means of potentiodynamic polarization and measurements of the temporal evolution of the corrosion potential, in a 0.5 M NaCl solution. The corrosion products in the sample surface were analyzed by Rutherford Backscattering Spectrometry (RBS), X-Ray Photoelectron Spectroscopy (XPS) and Auger Electron Spectroscopy (AES). It was found that the corroded surface had lost more Zn than Al. The surface was examined by SEM and it was seen that the corrosion products adhered to the surface cracks. It was found that the alloy with 2.12 wt% concentration of Ag had the best corrosion resistance in the electrolyte used, but no clear tendency with the Ag concentration was found.

The aim of this work is to investigate the long term (3000 exposure hours) tendency of passive layers on titanium to breakdown in Tani-Zucchi and Carter-Brugirard artificial saliva undoped and doped with chloride and fluoride ions. The non-uniformity of the saliva pH (from 7.88 to 5.73 and extreme case 2.15) was simulated. The following techniques were used: potentiostatic, potentiodynamic and linear polarization, the monitoring of the open circuit potentials vs. exposure time and atomic force microscopy. The breakdown (pitting) potential at about +2.9 V and the re-passivation potential at +2.4 V in Tani-Zucchi artificial saliva were determined. So, the pitting protection potential is very noble and can not be reached in human body.

High purity Al samples were implanted with 35 keV Cl+ then polarized in Cl--free electrolyte in order to ascertain corrosion behavior as a function of Cl content. Electrochemical data indicated implant fluences between 5x1015 and 2x1016 Cl+cm-2 resulted in little or no localized attack. Implant fluences of 3x1016 and 5x1016 Cl+cm-2 resulted in significant attack with the severity scaling as a function of implant fluence. The low variability in the behavior of localized corrosion for the 5x1016 Cl+cm-2 sample suggests that this implant dosage may result in a critical Cl- in the sample for pit nucleation. Optical and Electron microscopy images indicated some reactivity associated with lower fluences (1x1016Cl+cm-2), possibly indicating enhanced general dissolution. At high magnification the corrosion was observed to occur outside the implanted boundary through mechanisms of tunneling or altered local chemistry at those sites. The SEM images reveal a form of localized corrosion with a crystalline character.

The electrochemical behavior of chemically polished polycrystalline tin is investigated in borate buffer solutions at pH=7.5 using in-situ Raman measurements. Experiments reveal the appearance of “luminescence” under continuum red laser light only for a narrow range of sample potentials within the anodic plateau. The phenomenon is discussed in view of the tin oxides formed on the surface, and correlated with the assignation of the oxido-reduction processes observed in the voltammograms.

Copper is a critical material in electrical components and is subject to atmospheric sulfidation. This study characterized the product formed when Cu is exposed to a dilute (50-200ppb) H2S atmosphere at low (0.5%) to high (80%) relative humidity (RH). An important observation was that the Cu2S growth rate for long times is significantly higher for sulfides formed at low RH compared to high RH. In addition, it was found that for both low and high RH sulfidation, copper reacts to form the low chalcocite phase (Cu2S) as identified by x-ray and electron diffraction. Cross-section and plan-view TEM revealed that the Cu2S grains formed at high RH are 20-50 nm in size with a large amount of porosity, whereas the grains formed at low RH are 75-150+ nm and appear to undergo grain growth with little porosity as the film thickens.

Bismuth, a semi-metal with very long mean free path and large magnetoresistance (MR) effect, is a novel candidate material for thin film spintronic devices. Electrochemical deposition followed by a post-deposition anneal has resulted in highly textured bismuth films as characterized by x-ray diffractometry and pole figure measurements. A highly sensitive, real time in-situ stress measurement system was designed and employed to study stress generation during bismuth film growth. Bismuth films displayed a monotonically increasing compressive stress during deposition. The magnitude of the compressive stress decreased with the deposition rate in the range 1.5 Å/sec to 50 Å/sec.

We investigated the corrosion mechanism of copper films. Based on our results regarding the morphology of the Cu surface, examined by scanning electron microscopy (SEM) and focused ion beam (FIB), it is shown that with an inorganic acid-based model CMP solution corrosion is initiated at the grain boundaries. In contrast, for an organic acid-based solution, corrosion starts with no preferential location. Some of the samples received an additional anneal after the CMP process was completed to monitor the influence of annealing on the corrosion mechanism by the acid solutions. Presence of facets especially after treatment with the inorganic acid-based model CMP solution suggests that a different mechanism governs the initiation and the evolution of corrosion. Desorption of the impurities during annealing, which is monitored by Atmospheric Pressure Ionized Mass Spectrometry (APIMS) revealed desorbing species from the copper films that could originate from the additives used in the Cu plating bath.