Shearforce-Based Constant-Distance Scanning Electrochemical Microscopy as Fabrication Tool for Needle-Type Carbon-Fiber Nanoelectrodes

Abstract

Carbon fiber nanoelectrodes with nanometer radii tip curvatures were fabricated using a shearforce-based constant-distance scanning electrochemical microscope and electrochemically induced polymer deposition. A simple DC etching procedure in alkaline solution provided conically sharpened single carbon fibers with well-formed nanocones at their bottom. Coating the stems but not the end of the tips of the tapered structures with anodic electrodeposition paint was the strategy for limiting the bare carbon to the foremost end and restricting a feasible voltammetry current response to exactly this section. The electrodeposition of the polymer was prevented at the foremost end of the tip using a shearforce-based tip-to-sample distance control that allowed approaching the etched tips carefully in just touching distance to a film of a silicone elastomer. Analysis of the steady-state cyclic voltammograms in presence of a reversible redox compound revealed effective radii for the obtained needle-type carbon-fiber nanoelectrodes down to as small as 46 nm. The method offers an alternative pathway toward the fabrication of highly miniaturized carbon electrodes.

Shearforce positioning of nanoprobe electrode arrays for scanning electrochemical microscopy experiments

“…However, in a previous work [42], we deposited the electrophoretic paint with a different method and it formed a thinner insulating layer closer to the tip apex. Therefore, we believe that these SEM images do not allow visualizing precisely the radius of each electroactive tip because the border of the insulating paint could not be observed by SEM [47,51]. Another interpretation may be that the nanoprobes are not independent and diffusion layer overlapping is encountered along the whole nanoprobe array.…”

“…The protocol was then successfully used for the insulation of nanoelectrode arrays prepared from etched optical fiber arrays [43]. More recently, Schulte et al have shown that shearforce detection in SECM could be used as a fabrication tool for needletype carbon-fiber nanoelectrodes [47]. Following this work we would like to evaluate the interest of the shearforce positioning as described in the previous section as a tool for controlled insulation of gold nanotip array with electrophoretic paint.…”

Focused-Ion-Beam-Milled Carbon Nanoelectrodes for Scanning Electrochemical Microscopy

“…Electrochemically etched carbon nanoelectrodes (7) were employed as non-catalytic conductive supports of single platinum nanoparticles to study their electrocatalytic activities (8). Etched carbon-fiber nanoelectrodes, however, yielded only low SECM feedback responses (9) because of the conical tip geometry (10, 11). Alternatively, disk-shaped carbon nanoelectrodes (12) were developed by pyrolytic deposition of carbon (13).…”

“…Advantageously, the thin quartz sheath allows for high-resolution transmission electron microscopy (TEM) imaging of the flat and sharp carbon nanotips. The geometry of FIB-milled carbon nanotips is well-controlled not only to quantitatively assess their remarkably high electrochemical reactivity, but also to yield high feedback responses in SECM approach curve measurements in contrast to previously reported carbon nanotips (9, 14–17). Good agreement between experimental and simulated approach curves at SiO 2 -coated silicon wafers reliably confirms the well-characterized tip geometry and size, and a lack of a conductive carbon film on the outer tip wall.…”

Combined electrochemical-topographical imaging: a critical review

“…Here, the SECM probe is excited via lateral vibrations, either mechanically or by attachment to a tuning fork, and certain modes of these lateral oscillations are damped by hydrodynamic forces in proximity to a surface. 71,72 Detection of the shear-force dampening was initially achieved via optical means 97 but alternative detection systems have since been developed, as shown in Fig. 6a).…”