Plasma etching of superconducting Niobium tips for scanning tunneling microscopy

TL;DR

This paper presents a reproducible dry etching method using SF6 plasma to fabricate sharp superconducting Niobium tips for STM, enabling high-quality imaging and spectroscopy at cryogenic temperatures.

Contribution

The authors develop a self-sharpening dry etching technique for producing atomically sharp Nb tips suitable for STM and spectroscopy.

Findings

Tips have radii less than 100 nm.

Tips produce high-quality STM images and spectroscopy.

Technique works from 30 mK to 9 K.

Abstract

We report a reproducible technique for the fabrication of sharp superconducting Nb tips for scanning tunneling microscopy (STM) and scanning tunneling spectroscopy. Sections of Nb wire with 250 $\mu$m diameter are dry etched in an SF$_6$ plasma in a Reactive Ion Etcher. The gas pressure, etching time and applied power are chosen to produce a self-sharpening effect to obtain the desired tip shape. The resulting tips are atomically sharp, with radii of less than 100 nm, and generate good STM images and spectroscopy on single crystal samples of Au(111), Au(100), and Nb(100), as well as a doped topological insulator Bi$_2$Se$_3$ at temperatures ranging from 30 mK to 9 K.