Influence of electrode size and geometry on electrochemical experiments with combined SECM–SFM probes

Abstract

Gold electrodes integrated into silicon scanning force microscopy (SFM) probes allow the acquisition of spatially correlated data for sample morphology (via SFM) and local electrochemical reactivity via scanning electrochemical microscopy (SECM). The lateral resolution of both techniques is controlled by different properties of the integrated probes. The topographic tracking provided by the SFM mechanism allows the realization of very small working distances for the SECM measurements. Microfabrication technology was used in order to reduce the size of the active electrode area of the tip into the sub-100 nm regime. The functionality of the probes was tested using electrochemical methods. Experiments revealed that the response could be quantitatively compared to numerical simulation. The low working distance, in combination with the small size of the active electrode area, allows for high lateral resolution in the SECM images. This is illustrated with different model substrates that cover a range of different rate constants and illustrate the dependence of the SECM contrast on the local kinetics of the sample in the sub-micrometre size range.

Fabrication of soft gold microelectrode arrays as probes for scanning electrochemical microscopy

“…The distance between the working electrode and the substrate is defined by the thickness of the lamination foil, the exact geometry under which the cross-section was exposed and the inclination angle of the SECM holder under which the soft probe is approached. This is conceptually similar to the combined SECM-AFM probes of Kranz et al [13], and similar probes proposed afterwards [14,15] in which the distance of the active electrode area to the sample is kept approximately constant by a thorn that mechanically contacts the surface permanently or intermittently. The flexible polymeric probes were able to accommodate sample tilts without any additional electronic instrumentation or preliminary sample leveling [30].…”

“…There is a broad range of literature reports that have expanded the applicability of the technique to other interfaces such as liquid/liquid or liquid/gas [7], and have introduced new working modes such as the tip generation-sample collection [8,9] or the redox competition mode [10] for the investigation of specific catalytic reactions. Instrumental developments are actively pursued in different laboratories to increase the lateral resolution by integrating electrodes of nanometer extension into probes for scanning force microscopy [11][12][13][14][15], using the electrodes also as shear force sensors [16][17][18] or combining it with scanning ion-conductance microscopy [19]. These combined techniques help to maintain a constant working distance above curved substrates and samples that have a roughness and/or topography that are not negligible compared to the electrode size.…”

Local Evaluation of Processed Membrane Electrode Assemblies by Scanning Electrochemical Microscopy

“…An inclined ME does not reach the contrast expected from a parallel orientation of sample and ME due to a inefficient shielding of the diffusion from the solution bulk. 31,33 Furthermore, the diffusion of redoxactive species is unsymmetrically blocked close to the sample surface 35 while no significant deviations are expected in the bulk solution. During the imaging process in constant distance mode, the lateral distance between active ME area (for activity sensing) and the mechanical point of contact between the glass sheath and the sample surface (i.e.…”

Methods of photoelectrode characterization with high spatial and temporal resolution

“…If variations in the height of sample features are large compared to the tip/substrate gap distance, it becomes very difficult to distinguish differences in UME current caused by topology rather than electrochemical activity. When the desired UME tip/substrate separation distance is comparable to the roughness of the sample surface, several advanced versions of SECM may be employed, including scanning-force microscopy, 64 hybrid SECM/atomic-force microscopy (AFM), 65,66 intermittent-contact SECM, [61][62][63] and electron transfer/ion transfer SECM. 67 Although this section has focused on the implementation of SECM for the analysis of the spatial variation of product formation on photoelectrode surfaces, SECM can also be used to investigate local changes in pH 68 and corrosion processes, [69][70][71][72][73][74] analyze surface coverage of adsorbed intermediates (surface interrogation SECM), [75][76][77][78][79] and measure short-lived intermediates.…”