Electrochemical etching technique: Conical-long-sharp tungsten tips for nanoapplications

Abstract

This paper proposes an electrochemical etching technique to fabricate tungsten tips. Tips combining well-defined conical shape, a length as large as 2 mm, and sharpness with a radius of curvature of around 20 nm are fabricated using the proposed technique. These tips are needed in a variety of applications including multipoint contact measurements and nanomanipulation. The technique consists of three steps: the first is static etching, which creates a neck-in phenomenon on the wire; the second is dynamic etching, where the wire is oscillated up and down in the solution to form a long conical shape; finally, static etching is applied again to break the wire, and thus, sharp tips are produced. The best operating conditions of the process were experimentally obtained. These factors include the position of the cathode, the length of the immersed wire, and the applied voltage. The effects of these factors on the etching current and tip fidelity were also examined based on the measured etching current. In particular, the position of the cathode determines the strength of the electrical field near the air/solution interface; the immersed wire depth determines mainly the equivalent resistance of the process and thus controls the etching current; and the applied voltage defines the etching rate of the wire.

Simulation-guided nanofabrication of high-quality practical tungsten probes

“…3(c)) which is accepted by many papers. 29,[31][32][33]35,43 Since the electric eld is another factor that affects the maximum etching position on the tungsten wire, the actual necking position will vary in the meniscus with different electrodes.…”

“…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.…”

Hydrogel tip attached quartz tuning fork for shear force microscopy

“…The first step for the negative tip mold fabrication is to make a sharp tungsten tip by time-controlled electrochemical etching of a tungsten wire. This process is traditionally used to make a sharp metallic tip for scanning tunneling microscopy [7]. A ring electrode with the diameter of 3.5 cm is used to generate axisymmetric current flow around the immersed tungsten wire thus helps the etched tungsten tip to have an axisymmetric conical shape.…”