Using Wire Cutters to Make STM Tips

Reasonably good tips for Scanning Tunneling Microscopy (STM) can be produced by cutting tungsten or platinum iridium (PtIr) wire at a 45° angle with a pair of sharp wire cutters. The recommended wire diameter to use is 0.25 mm (0.010 inches). Wire with a diameter greater than 0.012 inches will not fit inside the STM Cartridge.

Materials Required:

• 0.25 mm tungsten or platinum iridium (PtIr) wire
• Wire cutters appropriate for the type/gage of wire
• Needle-nose pliers

To make a tip by cutting wire:

1. Cut off a piece of wire between 1 and 1.5" long using a strong pair of wire cutters.
2. Grip one end of the wire tightly with the needle-nose pliers.
3. Orient the wire cutters at a 45° angle relative to the wire as shown:

4. Cut the wire by using the wire cutters to pull and twist the end of the wire while snipping.

The resulting tip may not appear as sharp as it is. Tungsten STM tips oxidize fairly quickly and should be discarded after 1 to 2 days. PtIr STM tips do not readily oxidize and may be kept and used for a much longer time before degradation affects image quality.

The overall shape of tips made using wire cutters is not well-defined. STM images taken using these relatively blunt tips can show multiple tip imaging effects. Sharper, higher aspect ratio tungsten tips can be made using a tip etcher.

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