Simultaneous Intelligent Imaging of Nanoscale Reactivity and Topography by Scanning Electrochemical Microscopy

Abstract

Scanning electrochemical microscopy (SECM) enables reactivity and topography imaging of single nanostructures in the electrolyte solution. The in situ reactivity and topography, however, are convoluted in the real-time image, thus requiring another imaging method for subsequent deconvolution. Herein, we develop an intelligent mode of nanoscale SECM to simultaneously obtain separate reactivity and topography images of non-flat substrates with reactive and inert regions. Specifically, an ∼0.5 μm-diameter Pt tip approaches a substrate with an ∼0.15 μm-height active Au band adjacent to an ∼0.4 μm-wide slope of the inactive glass surface followed by a flat inactive glass region. The amperometric tip current versus tip–substrate distance is measured to observe feedback effects including redox-mediated electron tunneling from the substrate. The intelligent SECM software automatically terminates the tip approach depending on the local reactivity and topography of the substrate under the tip. The resultant short tip–substrate distances allow for non-contact and high-resolution imaging in contrast to other imaging modes based on approach curves. The numerical post-analysis of each approach curve locates the substrate under the tip for quantitative topography imaging and determines the tip current at a constant distance for topography-independent reactivity imaging. The nanoscale grooves are revealed by intelligent topography SECM imaging as compared to scanning electron microscopy and atomic force microscopy without reactivity information and as unnoticed by constant-height SECM imaging owing to the convolution of topography with reactivity. Additionally, intelligent reactivity imaging traces abrupt changes in the constant-distance tip current across the Au/glass boundary, which prevents constant-current SECM imaging.

Nanogap-Resolved Adsorption-Coupled Electron Transfer by Scanning Electrochemical Microscopy: Implications for Electrocatalysis

“…A sharp, flat, and damage-free tip was positioned at a distance, d , of ∼50 nm from the atomically flat HOPG surface, as established previously. , Specifically, an ∼1 μm-diameter Pt tip was surrounded by a thin glass sheath with an outer diameter of ∼2 μm and flattened by focused-ion-beam milling (Figure S2A). , The tip was protected from electrostatic damage, − as confirmed after SECM experiments (Figure S2B). The tip–HOPG distance was controlled precisely and quickly by measuring an approach curve in the intelligent mode , to prevent the tip–substrate contact (Figure S3) and minimize the fouling of the HOPG surface by residual contaminants in redox molecules, respectively.…”

“…33,34 The tip was protected from electrostatic damage, 35−37 as confirmed after SECM experiments (Figure S2B). The tip−HOPG distance was controlled precisely and quickly by measuring an approach curve in the intelligent mode 37,38 to prevent the tip−substrate contact (Figure S3) and minimize the fouling of the HOPG surface by residual contaminants in redox molecules, 28 respectively. The tip− substrate nanogap was maintained by minimizing the thermal drift of the tip by using a homebuilt isothermal chamber.…”

Study of the electrostatic repulsion of the carboxylic surface in the diffusion layer by scanning electrochemical microscopy

“…The current fluctuation in the upper right corner of the SECM image was attributed to the varied surface roughness of the polycrystalline gold substrate. [ 22–24 ] In Figure 3a, under acidic conditions, the tip current was between 1.79 and 1.38 nA, which was obviously larger than the limiting steady‐state diffusion current (1.2 nA). Because the amount of carboxylate that dissociated from the carboxyl groups under acidic conditions was negligible, electron tunneling occurred directly on the MPA SAM surface.…”

Recent Advances in the Glass Pipet: from Fundament to Applications

“…They found that the tunnelling current shows an exponential dependence on tip−substrate distance at slow tip approach rates. Recently, Jantz et al 120 developed the intelligent mode of SECM to simultaneously obtain separate reactivity and topography images of nonflat substrates with both reactive and inert regions. This method does not need specialized hardware, including a bifunctional probe.…”