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The surface area of nanoporous gold films of thickness up to 930 nm and pores tens of nanometers in size was characterized by various electrochemical methods, including Cu underpotential deposition (UPD), surface Au oxidation/reduction reaction, and electrochemical impedance spectroscopy (EIS). The different approaches provide surface area values that are comparable and, in all cases, linearly increasing with thickness. However, whereas Cu UPD and Au oxidation/reduction methods yielded surface area values in good quantitative agreement, estimates based on EIS measurements were found to be 1.5-1.75 times larger. This discrepancy is tentatively attributed to a higher specific capacitance of nanoporous gold, possibly due both to the presence of residual surface Ag and to the high curvature of the nanoporous structures, that may have different interfacial properties as compared to planar surfaces. [ABSTRACT FROM AUTHOR]

Abstract: Nb films have been magnetron sputtered onto quartz sheets oriented with respect to the target at angles varying between 0° and 90°, with 15° steps. Impedance plots have been obtained by contacting these films with aqueous Na2SO4, either at the open circuit potential or at a potential where Nb is covered by an anodic passive Nb2O5 film. As the target–substrate angle θ increases, the shape of the impedance plots changes from that of a smooth electrode to that of a porous one, characterised in the high frequency range by a straight line forming a 45° angle with the real axis. The surface roughness of the Nb deposits, calculated from their double layer capacity, is low and constant at low θ, significantly increases at θ =45°, goes through a maximum in the range 60–75° and drops at θ =90°. AFM surface profiling confirms this trend, but estimates a lower surface roughness. Attempts to obtain Nb deposits with a surface roughness less strongly dependent on θ have been made by performing the depositions under pulsed conditions or by heating the substrates at 400–600°C. Heating at the higher temperature was a fairly effective method for decreasing the roughness of deposits formed at large θ. [Copyright &y& Elsevier]

Porous PbO2 electrodes have been prepared by anodic codeposition of PbO2 particles with an electrochemically grown PbO2 matrix, with the aim of illustrating how composite deposition may be a suitable method for obtaining electrodes of large and controlled surface roughness. By exploiting the different crystal structures of PbO2, the composition of α-PbO2+β-PbO2 composites (i.e. composites with an α matrix and a β dispersed phase) has been determined by X-ray diffraction. It has been found that reliable indications on composition of deposits may be also obtained by measuring the current efficiency of the deposition process, which largely exceeds unity in the case of composites. This way, the dependence of the dispersed phase concentration in the deposits on current density and suspended particles concentration has been determined. The surface roughness of the composite electrodes has been estimated by electrochemical impedance spectroscopy. It was found to increase almost linearly with the deposition charge and reach limiting values as either the deposition current density or the suspended particles concentration are increased. [Copyright &y& Elsevier]

Abstract: Nanoporous gold (NPG) layers have been fabricated by silver leaching of Ag–Au alloys with different dealloying processes and working temperatures. Structural, compositional and optical properties of the different samples have been analyzed with several experimental techniques: scanning and transmission electron microscopy (SEM/TEM), electrochemical impedance spectroscopy (EIS), Rutherford back scattering (RBS), spectroscopic ellipsometry. A periodic pattern has been realized on samples surface with focused ion beam (FIB) lithography in order to exploit NPG metallic behavior for surface plasmon polaritons (SPPs) excitation. The plasmonic response of the several NPG gratings has been analyzed and related to structural properties and fabrication conditions. [Copyright &y& Elsevier]