In Situ Characterization of Ultrathin Films by Scanning Electrochemical Impedance Microscopy

Abstract

Control over the properties of ultrathin films plays a crucial role in many fields of science and technology. Although nondestructive optical and electrical methods have multiple advantages for local surface characterization, their applicability is very limited if the surface is in contact with an electrolyte solution. Local electrochemical methods, e.g., scanning electrochemical microscopy (SECM), cannot be used as a robust alternative yet because their methodological aspects are not sufficiently developed with respect to these systems. The recently proposed scanning electrochemical impedance microscopy (SEIM) can efficiently elucidate many key properties of the solid/liquid interface such as charge transfer resistance or interfacial capacitance. However, many fundamental aspects related to SEIM application still remain unclear. In this work, a methodology for the interpretation of SEIM data of "charge blocking systems" has been elaborated with the help of finite element simulations in combination with experimental results. As a proof of concept, the local film thickness has been visualized using model systems at various tip-to-sample separations. Namely, anodized aluminum oxide (Al2O3, 2-20 nm) and self-assembled monolayers based on 11-mercapto-1-undecanol and 16-mercapto-1-hexadecanethiol (2.1 and 2.9 nm, respectively) were used as model systems.

Electrochemical impedance spectroscopy in interfacial studies

“…In these techniques, the investigated electrode surface is scanned with a test microelectrode at a close proximity. During the scans some electric quantity is measured; for a recent development and nice EIS version see [30]. Lateral resolution is determined not only by the microelectrode distance but also by the activity of the neighborhood of the locally probed area.…”

Local electrochemical impedance spectroscopy: A window into heterogeneous interfaces

“…As a result, the impedance of the tipwhich is the contribution of the faradaic impedance ( 932 ), and the double layer capacitance, ( 932 ) -depends on the local impedance of the substrate, namely ;<= and ;<= [54]. It was successfully used to characterize oxide thin films [47,55], localized corrosion [53] as well as selfassembled-monolayer coated electrodes [55], or to distinguish single and double strand DNA [56]. However, although this type of measurement is sensitive to minute changes of the local impedance of the substrate, it is still difficult to perform quantitative analysis of the experimental data as the response depends on both the tip/sample local intrinsic capacitance and the frequency range used [55].…”

“…It was successfully used to characterize oxide thin films [47,55], localized corrosion [53] as well as selfassembled-monolayer coated electrodes [55], or to distinguish single and double strand DNA [56]. However, although this type of measurement is sensitive to minute changes of the local impedance of the substrate, it is still difficult to perform quantitative analysis of the experimental data as the response depends on both the tip/sample local intrinsic capacitance and the frequency range used [55]. A different way of performing local impedance spectroscopy using the SECM was devised for the characterization of the hydrogen evolution reaction at a Pt electrode [57,58].…”

Electrochemical Scanning Probe Microscopies in Electrocatalysis

“…Unlike the AC‐SECM, SEIM only applies the AC perturbation to the tip, then different sample surface domains with different electrochemical properties can be distinguished without disturbing the sample surface status. SEIM was reported to be capable of in situ local corrosion measurements and local film thickness visualization …”