SPMwikiGold tip etching 2017-06-16

A sharp metallic tip used for STM is usually obtained by electrochemical etching. I marked down the process of etching a gold tip in my lab for the future freshman.

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What you need:

• DC power supply
• Multimeter
• Etching stage
• Solution:Concentrated HCl:Ethanol=1:1 (in volume)
• Gold wires (D:0.25-0.35mm)

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schematic

References：
Kharintsev, S. S., Hoffmann, G. G., Fishman, A. I., & Salakhov, M. K. (2013). Plasmonic optical antenna design for performing tip-enhanced Raman spectroscopy and microscopy. Journal of Physics D: Applied Physics, 46(14), 145501.

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Connection

About 2.3V DC power was connected to the gold wire and a Pt-electrode.( Positive to gold,negative to Pt-electrode). A multimeter was in series with the circuit to monitor the etching current.(~mA)

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Etching

The Pt-electrode( usually was made to a cycle) is parallel to the solution level and the gold wire is insert into the solution about 1~2mm. When switching on the power, etching starts and we could see the etching current from the multimeter. When the current becomes zero, etching stops. Turn off the power and take out the tip.

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Result

This is a new tip made by the method above. After we get an idea tip, it must be ultrasonic cleaned with water and alcohol to remove the residual acid. The tip should be kept in alcohol solution for storage.

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Note:

To keep the Pt-electrode as clean as before, usually we need to exchange the polarity of the DC power to do another inverse etching.