Serguei Belochapkine

Characterization of Nanoporous Gold Electrodes for Bioelectrochemical Applications

The high surface areas of nanostructured electrodes can provide for significantly enhanced surface loadings of electroactive materials. The fabrication and characterization of nanoporous gold (np-Au) substrates as electrodes for bioelectrochemical applications is described. Robust np-Au electrodes were prepared by sputtering a gold-silver alloy onto a glass support and subsequent dealloying of the silver component. Alloy layers were prepared with either a uniform or nonuniform distribution of silver and, post dealloying, showed clear differences in morphology on characterization with scanning electron microscopy. Redox reactions under kinetic control, in particular measurement of the charge required to strip a gold oxide layer, provided the most accurate measurements of the total electrochemically addressable electrode surface area, A(real). Values of A(real) up to 28 times that of the geometric electrode surface area, A(geo), were obtained. For diffusion-controlled reactions, overlapping diffusion zones between adjacent nanopores established limiting semi-infinite linear diffusion fields where the maximum current density was dependent on A(geo). The importance of measuring the surface area available for the immobilization was determined using the redox protein, cyt c. The area accessible to modification by a biological macromolecule, A(macro), such as cyt c was reduced by up to 40% compared to A(real), demonstrating that the confines of some nanopores were inaccessible to large macromolecules due to steric hindrances. Preliminary studies on the preparation of np-Au electrodes modified with osmium redox polymer hydrogels and Myrothecium verrucaria bilirubin oxidase (MvBOD) as a biocathode were performed; current densities of 500 μA cm(-2) were obtained in unstirred solutions.

Study of Mixed Flowing Gas Exposure of Copper

This paper describes the results of copper coupons exposed to a class III mixed flowing gas environment MFG following the guidelines given by the Battelle Laboratory and the International Electrotechnical Commission for environmental testing. Corrosion products were studied in detail using scanning electron microscope, energy dispersive X-ray spectroscopy EDS, X-ray diffraction XRD, focused ion beam FIB, secondary ion mass spectroscopy SIMS, and transmission electron microscope. The weight gain measured after each exposure was compared with the weight gain calculated from the cathodic reduction of the corrosion layers and cross sectioning using an FIB. The result shows a relatively good correlation between the measured and the calculated experimental values of weight gain. As expected, within the first week, the different corrosion layers thickened until they formed a thick layer that became the determining step for further growth. After several days of exposure the Cu coupons developed a complex multilayered structure consisting of cuprous oxide Cu2S, cupric oxide CuO, copper sulfide Cu2S, covellite CuS, and evidence of antlerite 3CuO SO3 2H2O. No Cl-containing corrosion products were identified using XRD. However, EDS and SIMS analysis showed that Cl was distributed throughout the corrosion products, indicating that although Cl is inside the corrosion products, it is not part of the crystalline structure. Also, this suggests that Cl plays an important role in accelerating the corrosion of Cu during exposure to the MFG class III test.

Corrosion Resistance of Copper-Coated Contacts

Corrosion of electronic components can produce a wide range of failure signatures, from intermittent electrical faults to complete functional breakdown. This paper presents an investigation on the exposure of a simple connector-coating system. The system consists of a copper contact coated with a nickel layer underneath a gold finish layer. The system was characterized using the following techniques: optical microscopy, atomic force microscopy (AFM), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDAX), secondary ion mass spectroscopy (SIMS) and focused ion beam (FIB). After initial characterization, the connector was exposed to 2, 4, 7, 15, and 30 days in an aggressive environment consisting of 90% relative humidity, 40°C, and 4 ppm H 2 S. Digital images of the corrosion products that developed on the contacts after exposure clearly demonstrated localized corrosion by-products present on the connector surface. SEM, EDAX, and SIMS analysis of the corrosion sites demonstrated the presence of copper sulfide and nickel sulfur corrosion product, which suggest a two-step mechanism: first, the Ni layer is attacked by the aggressive environment at the sites where the gold layer is not available, followed by the diffusion of copper through the nickel layer. FIB cross-sectional analysis revealed that surface defects in the gold layer resulted in sites for corrosion initiation and subsequent development of a thick copper sulfide layer of approximately 5 μm. It is concluded that this copper connector coating system does not prevent the formation of insulating corrosion products on the surface of the connector in a very aggressive environment.

Microstructural Development of Copper Sulfide on Copper Exposed to Humid H2S

Pure copper samples were exposed in an environmental chamber for 2, 4, 7, 15, and 30 days at 90% relative humidity, 40°C, and 4 ppm hydrogen sulfide (H 2 S). Samples were subsequently subjected to microscopy and microanalysis using different techniques: scanning electron microscopy, energy analysis dispersive X-ray spectroscopy, X-ray diffraction, focused ion beam (FIB), and secondary ion mass spectroscopy. The corrosion samples were cross sectioned and the different corrosion layers were imaged using FIB. After 30 days exposure the predominant corrosion products were copper sulfide (Cu 2 S) and cuprite (Cu 2 O). Once the Cu 2 S reached a minimum thickness, the rate of growth of the layer became parabolic due to the limiting Cu + diffusion through a thickening film. As the layers reach a critical thickness (∼ 1000 nm) internal stresses and defects in the corrosion layer allow virtually free access of H 2 S and O to the underlying layers, consequently accelerating the film growth. ©2007 The Electrochemical Society. [DOI: 10.1149/1.2436612] All rights reserved.

A modified robotic system for catalyst preparation by wet or dry impregnation

A modified robotic workstation has been developed which is able to reproduce a conventional catalyst preparation method used routinely in our laboratory, thereby increasing significantly the number of catalysts that can be prepared at once. This paper describes some of the features of this modified system and outlines some of the difficulties encountered in transferring from manual to automatic operation. Some catalytic test results are given for the selective oxidation of propane over a catalyst consisting of Mo-V-Nb-W oxides supported on alumina which illustrate good reproducibility of data for samples prepared with the robotic system and a close similarity with data obtained with equivalent manually prepared materials.

Nanometer-scale physically adsorbed thermoresponsive films for cell culture

ABSTRACT Physical adsorption was used to produce nanometer thick thermoresponsive films with a view to nonenzymatic cell detachment. Two polymers were investigated, poly-(N-isopropylacrylamide) and poly (N-isopropylacrylamide-co-N-tertbutylacrylamide). Substrates were prepared above and below the polymers’ LCST to investigate the effect of polymer conformation on the prepared substrates. Endothelial cells were seeded on the prepared films; cell proliferation was higher on the films produced below the polymers’ LCST than on those prepared above and cells detached from the surfaces upon temperature reduction. Physical adsorption of poly-(N-isopropylacrylamide)–based films is a viable approach to produce substrates compliant with cell growth and temperature modulated detachment. GRAPHICAL ABSTRACT

Kirkendall void formation during room-temperature air-oxidation of thin aluminium and aluminium – lithium alloy films

Abstract The effect of room-temperature (~20°C) air-oxidation on void formation in sputter-deposited thin films of aluminum and its alloys was investigated using a transmission electron microscope. It was found that after air-oxidation, only lithium-bearing aluminum alloy films exhibited a high (~4 × 1016 cm−3) density of small (~2 nm) voids, whereas pure aluminum or lithium-free aluminum alloy films did not contain any voids. In lithium-bearing aluminum alloy films, both aluminum and lithium atoms migrate to the surfaces to form their surface oxide during room-temperature ageing after film deposition. In the course of the atom migration, excess vacancies are generated as a result of the large diffusivity difference existing between aluminum and lithium atoms (DLiinAl ≫ DAl) in the alloy matrix. The agglomeration of these excess vacancies led to the formation of so-called Kirkendall voids inside the alloy. Thus the presence of both aluminum and lithium in the alloys was a key factor for generating these Kirkendall voids in the films.