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

Abstract

Nanoscale scanning electrochemical microscopy (SECM) has emerged as a powerful electrochemical method that enables the study of interfacial reactions with unprecedentedly high spatial and kinetic resolution. In this work, we develop carbon nanoprobes with high electrochemical reactivity and well-controlled size and geometry based on chemical vapor deposition of carbon in quartz nanopipets. Carbon-filled nanopipets are milled by focused ion beam (FIB) technology to yield a flat disk tip with a thin quartz sheath as confirmed by transmission electron microscopy. The extremely high electroactivity of FIB-milled carbon nanotips is quantified by enormously high standard electron-transfer rate constants of ≥10 cm/s for Ru(NH3)63+. The tip size and geometry are characterized in electrolyte solutions by SECM approach curve measurements not only to determine inner and outer tip radii of down to ~27 and ~38 nm, respectively, but also to ensure the absence of a conductive carbon layer on the outer wall. In addition, FIB-milled carbon nanotips reveal the limited conductivity of ~100 nm-thick gold films under nanoscale mass-transport conditions. Importantly, carbon nanotips must be protected from electrostatic damage to enable reliable and quantitative nanoelectrochemical measurements.

Advances and Perspectives in Chemical Imaging in Cellular Environments Using Electrochemical Methods

“…This has also been reported for nanopipette-supported pyrolytic carbon tips [50]. Local relative humidity may explain why such effects are not always reported, since increased humidity will help to reduce ESD events, which may result in unintended ESD protection.…”

“…A carbon ring/platinum disk electrode or carbon ring/nanopore electrode can be fabricated in which the electrode surfaces are also exposed using FIB milling [65]. FIB milling of carbon nanoelectrodes, prepared by chemical vapor deposition (CVD), has enabled high-resolution SECM imaging [50]. Pt nanotips may also be shaped using FIB, to achieve a lower insulating sheath radius for use with SECM [66].…”

Fabricação, caracterização e aplicação de pontas de prova eletroquímicas multifuncionais para técnicas de microscopia de varredura de ponta de prova eletroquímica

“…Nanometre-size metal electrodes are known for being susceptible to ESD damage, 143 and lately ESD damage on carbon nanoelectrodes has been reported. 141 As ESD can be reduced (if not avoided) by a high humidity environment, 143 we can speculate that the lack of ESD damage is justified by high local humidity in the UK (typically 76%-89%) .…”

“…Electrochemical Scanning Probe Microscopy (EC-SPM) techniques such as Scanning Electrochemical Microscopy (SECM) are powerful tools for investigating surfaces and interfaces, exploring electrochemical activity and probing kinetics at the sub-micron level. [1][2][3] Recent advances dramatically improved EC-SPM spatial resolution to the order of a few nanometers, 25,84,141,142 opening the possibility of applying such techniques to single entities analysis, like single cells and single nanoparticles, [7][8][9][10][11] highresolution topographic mapping, 14,15 local ion flux, and local conductivity measurement, among others. 9,[16][17][18][19] The use of multifunctional probes, coupling more than one EC-SPM technique on a single probe, also extended further the experimental capabilities of those techniques making them attractive for a broad range of research subjects.…”

“…This method therefore eliminates the need for using FIB milling to cut the tips flush 57,72. FIB milling is not only a time-consuming and not widely available technique, but also can induce structural damage on carbon material as demonstrated by Baker et al57 Even under minimal exposure to the ion beam, FIB can introduce contamination to the electrode material by Gallium ions impregnation jeopardizing the electron transfer kinetics 141. The electronic controller, whereas, makes it possible to set different deposition times and temperatures for carbon deposition at the tip ends and the control the recession of the SECM tip.…”