Design and Performance of a Practical Variable-Temperature Scanning Tunneling Potentiometry System

TL;DR

This paper presents a highly sensitive variable-temperature scanning tunneling potentiometry system capable of mapping local electrochemical potentials with nanometer resolution, combining novel biasing and feedback techniques for optimal noise performance.

Contribution

The authors developed a practical STM potentiometry system with unprecedented voltage sensitivity and temperature versatility, enabling detailed surface potential studies at nanometer scales.

Findings

Achieved 130 nV voltage sensitivity in potentiometry measurements.

Enabled spatial resolution of local potentials down to 2 nm.

Operates effectively from liquid helium temperatures to room temperature.

Abstract

We have constructed a scanning tunneling potentiometry system capable of simultaneously mapping the transport-related electrochemical potential of a biased sample along with its surface topography. Combining a novel sample biasing technique with a continuous current-nulling feedback scheme pushes the noise performance of the measurement to its fundamental limit - the Johnson noise of the STM tunnel junction. The resulting 130 nV voltage sensitivity allows us to spatially resolve local potentials at scales down to 2 nm, while maintaining angstrom scale STM imaging, all at scan sizes of up to 15 um. A mm-range two-dimensional coarse positioning stage and the ability to operate from liquid helium to room temperature with a fast turn-around time greatly expand the versatility of the instrument. By performing studies of several model systems, we discuss the implications of various types of surface morphology for potentiometric measurements.