Wire Electrolysis Cell Holder For Etching Atomically Fine Probes

Concept

This holder clips on to a standard 40mm specimen sample pot and keeps a fine wire in suspension. The wire itself (typically 0.3mm to 0.8mm diameter, usually 0.3mm 316L stainless steel) is held in place by a croc clip on the tab above the central wire hole. Titanium wire is best, the author uses Nichrome 80, and 316 stainless steel will give a micron-sized sharp point though with a somewhat irregularly-etched haft. Braided electric fence line is another source of fine, stainless wire if vaping is illegal in your jurisdiction.

Preparation

Cut a bit of wire long enough to reach from the top of the tab to the desired height in the container. Poke the wire through the central hole, leaving the desired length sticking out, and clamp the rest of the wire to the tab with a croc clip. It is best to bend or wrap the wire slightly in such a way that it will not fall out when the croc clip is removed.

The container typically contains 5% sodium chloride solution, ideally very slightly acidified. If you have 1% nitric acid this will create a roughened probe body, ideal for holding more resin. It also needs another electrode, and for this I use a stainless steel teaspoon held to the container wall with another croc clip.

For a fine point clip the holder over the container and adjust the wire so that it is in the electrolyte for about 8mm but does not touch the spoon. Immersing less than this will cause shorter points or stepped points. More than this will result in etched sides and a rounded point. These attributes may be combined by etching in several steps.

Use

Connect 3xAAA batteries or a lab power supply, positive terminal to the wire, negative wire to the spoon. For thick probes of >0.6mm diameter, run until the probe tip is etched to the preferred sharpness, or carry on until the end falls off for a super fine point. For thin wire ~0.2mm, run the cell until the end drops off the wire and immediately stop the current. This technique with the right wire can form an atomically fine point.

If you are using acidified salt the solution remains clear enough to see what is happening, and you can halt the etch at the desired sharpness.

Remove the wire from the holder by disconnecting the croc clip and straightening the wire, then pulling it out point forward, thus avoiding knocking it on the plastic holder.

Very gently wash the tip with hot water (preferably distilled), and spray with isopropyl alcohol or acetone to remove excess water before air-drying. The probe can now be mounted in a holder such as found here https://www.printables.com/model/867526.

Notes

Prints flat with no support. Photos show a Nichrome 80 tip next to 22ga hypodermic needle point,  the irregularities on a stainless steel 316 point, a selection of etched tips, and an achieved micron scale etching done with the Nichrome probe. Designed for The RepRapMicron Project.