Synchronous Electrical Conductance‐ and Electron Tunnelling‐Scanning Electrochemical Microscopy Measurements

Abstract

The requirement to separate topographical effects from surface electrochemistry information is a major limitation of scanning electrochemical microscopy (SECM). With many applications of SECM involving the study of (semi)conducting electrode surfaces, the hybridisation of SECM with scanning tunnelling microscopy (STM) or a surface conductance probe would provide the ultimate topographical imaging capability to SECM, but previous attempts are limited. Here, the conversion of a general scanning electrochemical probe microscopy (SEPM) platform to facilitate contact electrical conductance (C)‐ and electron tunnelling (T)‐SECM measurements is considered. Measurements in air under ambient conditions with a Pt/Ir wire tip are used to assess the performance of the piezoelectric positioning system. A hopping‐mode imaging protocol is implemented, whereby the tip approaches the surface at each pixel until a desired current magnitude is exceeded, and the corresponding z position (surface height) is recorded at a set of predefined xy coordinates in the plane of the surface. At slow tip approach rates, the current shows an exponential dependence on tip‐substrate distance, as expected for electron tunnelling. For measurements in electrochemical environments, in order to overcome well‐known problems with leakage currents at coated‐wire tips used for electrochemical STM, Pt‐sensitised carbon nanoelectrodes are used as tips. The hydrogen evolution reaction on 2D Au nanocrystals serves as an exemplar system for the successful simultaneous mapping of topography and electrochemical activity.

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

“…The tip current enhanced by redox-mediated electron tunneling was used only for the termination of the tip approach and was excluded during the post-imaging fit of approach curves (e.g., Figure C). By contrast, the tip current enhanced by solvent-mediated electron tunneling was used in a recent study to separately image the substrate topography from the substrate reactivity, which was imaged in the feedback mode at a longer distance . The combination of SECM with STM requires a conductive substrate in contrast to the intelligent mode based only on the SECM feedback mechanisms.…”

Probing Activities of Individual Catalytic Nanoflakes by Tunneling Mode of Scanning Electrochemical Microscopy

“…Unlike conventional tunneling experiments ( e.g. , STM junctions and electrochemical STM − ), in the tunneling mode of SECM, no voltage is applied between the tip and the substrate, and the tip current at short separation distances is due to the electrochemical reaction occurring at the nano-sample surface (Scheme A). As an SECM tip approaches a conductive particle attached to an insulating support, the tunneling resistance decreases exponentially with decreasing separation distance ( d ), and the tip potential begins to drive the charge-transfer process at the NP/solution interface. , The particle potential changes over ∼2 nm tip displacement from the open circuit value to the tip potential ( E T ) value, and the metal NP begins to act as a part of the nanoelectrode.…”

Simultaneous Observation of Faradaic and Tunneling Current at a Flat Surface Using Tunneling-Current-Based Constant-Distance Scanning Electrochemical Microscopy with a Platinum Nanoelectrode

“…Recent advances have enabled the distance between sample surfaces and probes 1 to be controlled with nanometer-level accuracy using shear force, 2,3 intermittent contact, 4 ion conductance, 5 atomic force, 6 and tunneling current. [7][8][9][10] Furthermore, with advances in probe miniaturization technology, the resolution of SECM has been improved to the nanometer scale. 1,9,[11][12][13][14][15][16] Consequently, a method is needed for the facile and reproducible preparation of nanoelectrodes.…”

“…[7][8][9][10] Furthermore, with advances in probe miniaturization technology, the resolution of SECM has been improved to the nanometer scale. 1,9,[11][12][13][14][15][16] Consequently, a method is needed for the facile and reproducible preparation of nanoelectrodes.…”

“…22 Researchers have also fabricated small-RG-ratio nanoelectrodes by electroplating 25 and electroless-plating 8,26 of metals inside nanopipette walls. Platinum deposition over nanometer sized electrodes has been reported for STM/SECM tips 9 SECM/SICM tips 27,28 to enhance electrochemical responses.…”