Local etching of copper films by the Scanning Electrochemical Microscope in the feedback mode: A theoretical and experimental investigation

Effect of Redox Mediators on Corrosion Behavior and Scanning Electrochemical Microscopy Response

Scanning electrochemical microscopy (SECM) is widely used to measure local electrochemical reactivity of corroding surfaces. A major criticism of using SECM in feedback mode for corrosion studies is the requirement of an external redox mediator (RM) as it could react with the metal and affect the Nernst potential at the metal-solution interface. Consequently, it becomes challenging to differentiate the interference caused by the RM from the local reactivity of the metal. Herein, a multiscale electrochemical approach is presented to investigate the effect of RM choice on the corroding substrate. Two common RMs, ferrocenemethanol and hexaammineruthenium(III) chloride, were used to perform SECM over copper and aluminum. It was found during macroscale electrochemical measurements that Ru(NH)63+ acted as an oxidant and promoted corrosion. The SECM feedback behavior varied for copper depending on the RM used, suggesting that the corrosion reactions controlled the negative feedback mechanism, not the formation of an insulating passive film. The passivated aluminum surface consistently exhibited negative feedback, regardless of the RM used. SECM approach curves also displayed a distortion in the steady state current, which was caused by the deposition of substrate-generated species on the microelectrode. These deviations in feedback response were accounted for during analysis through incorporation into a finite element model to accurately extract the RM kinetic rate constants. The importance of understanding these processes is highlighted to avoid misinterpretation of passive behavior and advances toward a more quantitative use of SECM for corrosion studies.

Nano‐silica/chitosan composite coatings on biodegradable magnesium alloys for enhanced corrosion resistance in simulated body fluid

Chitosan (CTS) coatings have been studied as a biocompatible coating on biodegradable magnesium (Mg) alloys to improve the corrosion resistance and bioactivity for medical implants. However, the loose structure of the CTS coating cannot provide ideal long‐time corrosion resistance in the physiological environment. In this study, a nano‐SiO2/CTS composite coating was applied on an Mg alloy substrate using the sol–gel method. The surface characteristics of the samples were examined by Fourier‐transform infrared analysis, X‐ray diffraction, scanning electron microscopy‐energy‐dispersive spectrometry, and contact angle measurements. The particle size and suitable dispersion of the SiO2 nanoparticles inside the composite coating were confirmed by transmission electron microscopy. Further, the corrosion protection behavior of the coatings was examined in a simulated body fluid using potentiodynamic polarization, electrochemical impedance spectroscopy, and scanning electrochemical microscopy analyses. Atomic force microscopy was used to determine the surface morphologies of the samples after the polarization test. The surface characteristics, electrochemical measurements, and immersion test revealed that the SiO2 nanoparticles effectively filled the voids of the CTS coating and significantly improved the corrosion resistance. The optimal concentration of nano‐SiO2 is 1.0 g/L.

Evaluation of the corrosion behavior of AZ31 magnesium alloy with different protein concentrations

Purpose

The purpose of this paper is to study systematically the corrosion behavior of AZ31 magnesium (Mg) alloy with different concentrations of bovine serum albumin (BSA) (0, 0.5, 1.0, 1.5, 2.0 and 5.0 g/L).

Design/methodology/approach

Electrochemical impedance spectroscopy and potential dynamic polarization tests were performed to obtain corrosion parameters. Scanning electrochemical microscopy (SECM) was used to analyze the local electrochemical activity of the surface film. Atomic force microscope (AFM), Scanning electron microscope-Energy dispersive spectrometer and Fourier transform infrared spectroscopy were used to determine the surface morphology and chemical composition of the surface film.

Findings

Experimental results showed the presence of BSA in a certain concentration range (0 to 2.0 g/L) has a greater inhibitory effect on the corrosion of AZ31, however, the presence of high-concentration BSA (5.0 g/L) would sharply reduce the corrosion resistance.

Originality/value

When the concentration of BSA is less than 2.0 g/L, the corrosion resistance of AZ31 enhances with the concentration. The adsorption BSA layer will come into being a physical barrier to inhibit the corrosion process. However, high-concentration BSA (5.0 g/L) will chelate with dissolved metal ions (such as Mg and Ni) to form soluble complexes, which increases the roughness of the surface and accelerates the corrosion process.

A multifunctional coating with modified calcium phosphate/chitosan for biodegradable magnesium alloys of implants

A novel CaP/CTS coating was prepared for enhanced corrosion resistance, cytocompatibility and antibacterial property of the biodegradable Mg alloys.

Photoassisted Electrochemical Micropatterning of Gold Film

Electrochemical etching is a powerful and popular method for fabricating micropatterns on metal substrates for use in electronic devices, electrochemical sensors, and plasmonic substrates. In order to achieve micropatterning, either a prepatterned insulating layer (mask) or a scanning microelectrode is often required to selectively trigger electrochemical etching at the desired locations. In the present work, we employed a well-focused light beam to enable the photoassisted electrochemical etching of gold film with a spatial resolution close to the optical diffraction limit (∼300 nm). It was found that the simultaneous application of light irradiation and appropriate potential were critical for the oxidative dissolution (i.e., etching) of gold to occur. Superior controllability of light beam allowed for the direct-write micropatterning without the need of mask or probe. Etching kinetics and mechanism were also studied by monitoring the dynamic evolution of optical transparency with a conventional transmission bright-field microscope, together with characterizations on the as-obtained patterns with atomic force microscopy and electron microscopy. This study is anticipated to contribute a feasible method for the micropatterning of gold film with implications for nanoelectronics and electrochemical sensors.