Review—Micro/Nanoelectrodes and Their Use in Electrocrystallization: Historical Perspective and Current Trends

Abstract

Crystallization is at the heart of many industrial processes in pharmaceuticals, dyes and pigments, microelectronics, and emerging wearable sensors. This paper reviews nucleation and early-stage crystal growth activated by an electrical pulse at microelectrodes and nanoelectrodes. We review thermodynamic and kinetic theories of electrochemistry developed around microelectrodes. We describe various methods to make microelectrodes and nanoelectrodes. Fundamental understanding is still needed for predicting and controlling nucleation and early-stage crystal growth. Using nanoelectrodes, nucleation and growth kinetics can be studied on one nucleation site at a time. In contrast, on macroelectrodes, nanoparticles are nucleated at random sites and at different times. This gives rise to overlapping growth zones resulting in inhomogeneous particle deposition and growth. The random size and density distributions prevent electrodeposition from being widely adopted as a manufacturing tool for making nanodevices. We describe advances in electrodeposition of metal nanoparticles and organic charge-transfer complexes on micro/nanoelectrodes. We anticipate increased interests in applying electrochemistry for making nanodevices particularly nanosensors and nanosensor arrays. These electrochemically fabricated nanosensor arrays will in turn fulfill the promise of nanoelectrodes as the most advanced analytical tools for medical diagnostics, environmental monitoring, and renewable energy.

Toward Precision Deposition of Conductive Charge‐Transfer Complex Crystals Using Nanoelectrochemistry

“…Nanoelectrochemistry using micro‐ and nanoelectrodes enables fundamental understanding of discrete nucleation events without complication from overlapping growth zones formed at different times. [ 11 ] Nanoelectrochemistry has been used to study nucleation of nanobubbles [ 12 ] and metal nanoparticles (down to one atom at a time). [ 13 ] The small electrode size also makes it easier for molecular simulations of the nucleation mechanisms.…”

Microelectrode‐enabled Electrocrystallization of Cobalt TCNQ Complex for Gas Sensing

“…Chronoamperometry on a microelectrode was used to investigate the crystal growth process of Co‐TCNQ with the composition of Co(TCNQ) 2 (H 2 O) 2 . The microelectrode enables monitoring the growth kinetics by limiting the number of nucleation sites, thus allowing the observation of the growth kinetics of individual crystals [18,23] . We conducted ex‐situ SEM imaging of the Co‐TCNQ crystals by removing the Pt microdisk electrode from the electrochemical cell at different times during Co‐TCNQ electrodeposition and gently rinsing it with MeCN before imaging.…”

“…As the growth time extends, multiple rodlike individual primary crystals grew radially outward towards the bulk solution from the electrode surface, closely resembling the hemispherical diffusive field near a microdisk electrode as illustrated by Figure 4c. [23] The growth time required to develop the hemispherical structure is potential dependent. For example, we only observe a clear pattern of radial growth after 1,200 s for h = 190 mV (Figure 4a); while crystals became radially oriented from the electrode surface only after 25 s for h = 270 mV (Figure 4b).…”

Micro- and nano-devices for electrochemical sensing

“…Thereafter, the electrode tip is exposed by mechanically polishing or chemically etching of the insulator. Technical aspects and recent advancements in carbon nanoelectrode fabrication, including the flame-etching of carbon microfibers, chemical vapor deposition (CVD) of a carbonaceous layer inside of pulled quartz capillaries with methane gas as a precursor, and pyrolysis of a propane/butane gas mixture have extensively been reviewed elsewhere [ 15 , 16 , 21 ]. On the other hand, the chip-like miniaturized structure has evidently benefited from the rapid evolution of microelectronics and the integrated circuit industry and relies on thin-/thick-film techniques employed in bottom-up manufacturing technologies including physical vapor deposition, photolithography, electron-beam lithography, and focused ion beam (FIB) milling.…”