Automatic shutdown system of alternating current electrochemical etching for the preparation of a platinum/iridium tip for scanning tunneling microscopy and the investigation of the byproduct of platinum chloride particles

Abstract

The automatic shutdown system of alternating current (AC) etching for fabricating platinum/iridium (Pt/Ir) wire to produce a tip used for scanning tunneling microscopy (STM) has been developed. We have modified a conventional automatic shutdown system of direct current (DC) etching, usually used for producing a tungsten STM tip, by adding the rectifying circuit and relay switching circuit. The development of the automatic AC shutdown system enabled us to produce the sharp Pt/Ir STM tips with high reproducibility. Also, the byproducts of the platinum chloride particles during the electrochemical etching process were investigated. The shape and the average size of the platinum chloride particle made from the ribbon electrode was tabular and 20 μm and those from the wire electrode was granular and 5 μm, estimated from scanning electron microscope (SEM) images, whereas the average of the core platinum crystalline particles was 4 nm, estimated from X-ray diffraction (XRD) using the Debye-Sherrer equation. The size and shape of the particles were controlled with AC frequency and the shape of the etched metal electrode. The developed production method of platinum chloride particles using inexpensive chemicals implements the process of the fabrication with simple apparatus.