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Abstract: A model of the Scanning Electrochemical Microscope (SECM) as a lithographic tool is presented and used to get quantitative kinetic information from lithographic experiments. It is illustrated in the specific case of the local etching by anodic dissolution of a copper substrate by the SECM in the feedback mode. A theoretical model presents the expected profile of the etched hole in the simple case of the positive feedback behaviour. A steady-state behaviour is expected for the dimensionless shape of the hole, which depends only on the tip-substrate separation distance. The hole depth is then expected to linearly depend on the etching time. The model is then confronted to different experimental conditions where a Cu substrate is locally oxidized by a tip-electrogenerated Fe(bpy)3 3+ oxidant. The experiments agree with the theoretical predictions (steady-state dimensionless profile and linear evolution of the depth with time). Even though the system behaves under positive feedback, the kinetics of the etching process can readily be extracted from the hole characterization and its conversion into Faradaic yield. [Copyright &y& Elsevier]

Abstract: Accuracy of kinetics characterization from SECM feedback experiments is carefully discussed. The experimental conditions that lead to the best accuracy are thus detailed on the basis on theoretical results. A recently published experimental study is also used to illustrate the discussion. Three different experimental characteristics of the SECM data acquisition are examined and discussed in this work: the geometrical characteristics of the microdisk tip, the tip-substrate distance range and the influence of an error on the zero tip-substrate distance. The best experimental conditions are encountered with the combination of results coming from approach curves with tips having Rg values larger than 10 on the 0.1–2 tip-substrate distance range and different radius, leading to a dimensionless kinetic parameter in the 0.10–1.8 range and through fit procedure with two adjustable parameters considering the zero tip-substrate distance as unknown. [ABSTRACT FROM AUTHOR]

Abstract: The theory for the analysis of redox enzymatic activity, under the condition of enzymatic substrate saturation, in SECM feedback mode has been reexamined. The conditions of validity for the different limiting cases have been established and discussed. Thanks to this analysis, we present different methods for determining the kinetics parameters from approximate analytical expressions without having to return to the numerical simulations. It was found that real zero order does not really exist, as first-order behaviour is always present at substrate sufficiently far from the center of the electrode. [Copyright &y& Elsevier]

The present article introduces a rapid, very sensitive, contactless method to measure the local surface conductivity with Scanning Electrochemical Microscopy (SECM) and obtain conductivity maps of heterogeneous substrates. It is demonstrated through the study of Graphene Oxide (GO) thin films deposited on glass. The adopted substrate preparation method leads to conductivity disparities randomly distributed over approximately 100 μm large zones. Data interpretation is based on an equation system with the dimensionless conductivity as the only unknown parameter. A detailed prospection provides a consistent theoretical framework for the reliable quantification of the conductivity of GO with SECM. Finally, an analytical approximation of the conductivity as a function of the feedback current is proposed, making any further interpretation procedure straightforward, as it does not require iterative numerical simulations any more. The present work thus provides not only valuable information on the kinetics of GO reduction in mild conditions but also a general and simplified interpretation framework that can be extended to the quantitative conductivity mapping of other types of substrates. [ABSTRACT FROM AUTHOR]

Abstract: A simple modification of the setup for shearforce control in SECM is proposed. It allows alternately SECM experiment and electrode manipulation and polishing. The good reproducibility of the measurement allows studying some parameters affecting the characteristics of the shearforce signal. A simple protocol is proposed to determine the resonant frequency using the current measurement and to select the optimal frequency for application in SECM. The length of the shearforce approach curve can vary from several hundred of nanometers to several μm when operating under hydrodynamic control. As shown in this study, the combination of the shearforce signal with the electrochemical feedback measurement allows the determination of the tip-to-sample distance, the apparent disk geometry of the probe and a larger range of heterogeneous kinetics constants. In principle, the proposed protocol is applicable to any SECM experiment involving a non-electrochemical positioning, e.g. AFM-SECM. [Copyright &y& Elsevier]

Fabrication of scanning electrochemical microscopy (SECM) tips cannot always guarantee a perfect disk geometry. In the present work, the impact of these defaults is investigated both theoretically and experimentally. The situations where these defaults can accurately be taken into account by considering that the probe behaves like a microdisk with effective geometric parameters are determined. In these situations, the quantitative analysis of the experimental results is greatly simplified. The study also proposes expressions to evaluate the apparent microdisk parameters from a picture of the probe. [ABSTRACT FROM AUTHOR]

The scanning electrochemical microscope (SECM) in the lithographic mode is used to assess quantitatively, from both theoretical and experimental points of view, the kinetics of irreversible transformation of electroactive molecular moieties immobilized on a surface as self-assembled monolayers (SAMs). The SECM tip allows the generation of an etchant that transforms the surface locally and irreversibly. The resulting surface patterning is detectable by different surface analyses. The quantification of the surface transformation kinetics is deduced from the evolution of the pattern dimensions with the etching time. The special case of slow etching kinetics is presented; it is predicted that the pattern evolution follows the expansion of the etchant at the substrate surface. The case of a chemically unstable etchant is considered. The model is then tested by inspecting the slow reductive patterning of a perfluorinated SAM. Good agreement is found with different independent SECM interrogation modes, depending on the insulating or conducting nature of the covered substrate. The surface transformation measurements are also compared to the reduction of solutions of perfluoroalkanes. The three-orders-of-magnitude-slower electron transfer observed at the immobilized molecules likely describes the large reorganization associated with the generation of a perfluoroalkyl-centered radical anion. [ABSTRACT FROM AUTHOR]

Abstract: The adsorption of 4-nitrobenzenediazonium tetrafluoroborate (NBD) in acidic aqueous solution was investigated by scanning electrochemical microscopy (SECM) on polycrystalline gold and glassy carbon (GC) substrates. The feedback mode of SECM was used to study the local properties of each substrate before and after immersion in the aryldiazonium solution, by performing approach curves with two redox mediators, and . The fitting of the approach curves with analytical approximate equation was used to evaluate the apparent heterogeneous rate constant k for redox system at NBD-adsorbed GC (k =2.6×10−4 cms−1). [Copyright &y& Elsevier]