Electrochemical preparation of tungsten tips for a scanning tunneling microscope

Abstract

We present experimental results obtained during the electrochemical preparation of tungsten tips for a scanning tunneling microscope. Experiments were done with direct current and two kinds of electrolytes widely reported in the literature: KOH and NaOH. We report the effects of the applied voltage, time of etching, tip length, electrolyte concentration, wire diameter, and immersed portion as relevant parameters in the process. From the images obtained by a metallurgical microscope and a scanning electron microscope as well as from Auger and electron diffraction x-ray analysis the best conditions for W tip preparation were obtained. We found that KOH is better than NaOH as an electrolyte to prepare tips for scanning tunneling microscopy and that tip quality increases as the wire diameter and the immersed portion increases.

Ultra-sharp metal and nanotube-based probes for applications in scanning microscopy and neural recording

“…[3][4][5][6][7] However, tungsten surface oxidation proves to be an issue when electrical conductivity between the sample and the probe is required. Post-etching treatment in hydrofluoric acid was proposed, 8 but in our experience, this method provided little improvement in tip-to-surface conductivity.…”

Novel electrochemical method of fast and reproducible fabrication of metallic nanoelectrodes

“…Considering NaOH as a well-suited electrolyte for the electropolishing of tungsten wires, the effect of its concentration was studied in the range of 0.5-4 M. [29][30][31] The concentration of 1 M was considered to be optimal because it ensures a good balance between tip curvature radius and surface roughness. Lower concentrations contributed to a higher tip curvature radius and lower aspect ratio, while stronger electrolytes tend to yield higher surface roughness (Fig.…”

“…(1) and (2) for the case of tungsten. [11][12][13][14][15][16][17][18][19][20][21] Cathode reaction :…”

Dynamic electrochemical-etching technique for tungsten tips suitable for multi-tip scanning tunneling microscopes

“…Especially, electrochemical etching of a tungsten wire is widely used for STM tips [54][55][56][57][58][59][60][61][62][63][64][65][66]. Thanks to contributions from many researchers, sharp tungsten tips having around 20-nm diameter at the apex can now be acquired routinely [64][65][66].…”

“…One of the common and reliable methods is so called a "drop-off" method, in which etching occurs at the air-electrolyte interface, causing the portion of wire immersed in the solution to "drop off" when its weight exceeds the tensile strength of the etched wire metal neck [28][29][30][31][32][33][34][35][36][37][38][39][40][41][54][55][56][57].…”