Tag: George Nazin

Silver Tip Preparation for Scanning Tunneling Microscopy

Presenter: William Crowley

Mentors: Ben Taber and George Nazin, Chemistry

Poster: 15

Major: Chemistry

Scanning tunneling microscopy (STM) can be utilized to image, manipulate, and spectroscopically characterize individual atoms and molecules. The scanning probe used in STM is often described as a tip. Tips are conically shaped pieces of metal that are, ideally, atomically defined at one end. Creating well defined tips is essential to obtaining quality STM images. Due to its spectroscopic enhancing plasmonic properties silver is an interesting material for STM. Specifically, enhancements to the factor of 106 to 107 have been reported. The Nazin group has developed a novel method of electroetching sliver to produce well defined STM tips. In our process we utilize a previously unused electrolyte; 1:8 glacial acetic acid to deionized water. Our two-step process first involves an automated primary electrochemical etch in which a 0.5 mm 9.9985% silver wire is etched to form a rough conical shaped. Second, the roughly shaped silver wire is manually etched to produce a well-defined apex. My research has focused on optimizing and parametrizing variables in this two-step process such as voltage bias and rate of etching. Finished tips are then characterized by scanning electron microscopy and energy dispersive x-ray spectroscopy. This process has yielded tips with an apex of approximately 200 nm.

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

Presenter: William Crowley

Co-Presenter: Ariel Rosenfield

Faculty Mentor: George Nazin, Ben Taber

Presentation Type: Poster 54

Primary Research Area: Science

Major: Chemistry

Funding Source: UROP Mini Grant, Univesrity of Oregon, $1,000

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 om 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 describe 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 which may lead to more efficient solar panels or smaller computer circuits.