Optimization of AC Electrochemical Etching for Fabricating Tungsten Nanotips with Controlled Tip Profile

Abstract

AC electrochemical etching in diluted potassium hydroxide (KOH) solution was optimized to fabricate tungsten (W) nanotips with a controllable sharpness and aspect ratio using an additional lift-up step. The final tip profile was dependent on the extent of interaction between the KOH solution and the side of the W surface, and effective bubble shielding effects near the apex region during the lift-up. Lateral etching rate along the W material was affected by parameters such as electrolyte–cathode positioning, etching voltage, and electrode size that influenced the flow or replenishment rate of OH− ions to the W surface submerged in the solution and at the meniscus region. With the lift-up step, the dense layer of bubbles that formed during etching could provide a good shield in minimizing the etch-back effects on the tip apex. Combining the above investigated effects, sharp nanotips with the required aspect ratio could be achieved with the enhanced lateral etching and the protective shield of bubbles.

Rapid Fabrication of High-Aspect-Ratio Platinum Microprobes by Electrochemical Discharge Etching

“…Y. Khan et al [ 21 ] and S.L. Toh et al [ 22 ] fabricated sharp tungsten tips with a dynamic electrochemical etching process with an additional lift-up step and DC [ 21 ] or AC [ 22 ] power supply. Results from both groups show that a low voltage is necessary to obtain the “neck-in” structure at the liquid-air interface.…”

Simulation-guided nanofabrication of high-quality practical tungsten probes

“…DC voltage is chosen to be applied to the electrodes since it is more favourable to prepare probes with both high aspect ratio and nanoscale tips. 30 A DC power source (B2091A, Keysight, USA) supplies different power modes to the tungsten anode and the ring copper cathode. Both the monitor and the power source could be programmed by the computer so that we can accurately control the motion of anode and immediately cut off the power once the immersed part of tungsten wire detaches from the upper part.…”

“…With the drop-off method, the inuence of different etching parameters on the prole and roughness of the probes have been explored, including strategies for the applied voltage between electrodes, mass of immersed part, relative location of electrodes, motion modes of the anode and electrolyte concentration. [29][30][31][32] Meanwhile, various probes have been fabricated to meet different demands. For example, Li et al fabricated different probes with controllable aspect ratio based on the investigation on the relation between pulling up speed, time and aspect ratio.…”

Electrochemical etching of lightweight nanotips for high quality‐factor quartz tuning fork force sensor: atomic force microscopy applications

“…Several properties such as high mechanical strength, durability, high conductivity (for scanning tunnelling, field-ion microscopy and Kelvin probe microscopy) and reliability are important for the nanotips. Tungsten has high mechanical strength, low cost and its electrochemical etching is straightforward, therefore, it is widely used for tip fabrication [23][24][25][26][27][28][29][30].…”

“…However, shaft size of the DC etched nanotips is large and massive. On the other hand, several dynamic etching techniques are explored [21][22][23][24][25]. Ju et al [24] proposed a method to dynamically control the neck-in position of a tungsten wire to fabricate nanotips with desirable lengths.…”