Electrochemical Etching of Silver Scanning Tunneling Microscope Tips in Dilute Acetic Acid

Abstract

Scanning Tunneling Microscopy (STM) is used to image, manipulate, and spectroscopically characterize individual atoms and molecules to further develop an understanding of materials that have application in the semiconductor field. The fabrication of sharp and smooth metallic tips plays an essential role in STM as the radius of curvature of tips used in STM directly influences resolution. The smaller the radius of curvature, the finer the resolution. We report a reproducible fabrication procedure of silver STM tips. Silver wire is electrochemically etched using an environmentally benign electrolyte solution of volume ratio 1:8 glacial acetic acid:deionized water to form a blunt cone. The roughly shaped tip is then manually electropolished to yield a sharp and smooth cone shape. The tip is then heated at 300°C to remove contaminates such as silver oxide. Silver is used for its plasmonic enhancing properties. The elemental purity and small radius of curvature (~100nm) of silver tips permits atomically resolved STM imaging, as well as photon emission and ultrafast electron emission measurements. These measurements, which would not be possible with previous materials used as STM tips, such as tungsten, will allow for a better understanding of potential semiconductor materials.