High Dynamic Range Scanning Tunneling Microscopy

TL;DR

This paper presents a method to enhance the dynamic range of scanning tunneling microscopy by actively canceling nonlinear current harmonics, enabling improved spectroscopy and imaging without hardware modifications.

Contribution

The authors introduce a phase-synchronized harmonic cancellation technique that significantly increases STM dynamic range using only electronic adjustments.

Findings

Enhanced dynamic range in STM measurements

Effective harmonic cancellation without hardware changes

Improved spectroscopy and imaging capabilities

Abstract

We increase the dynamical range of a scanning tunneling microscope (STM) by actively subtracting dominant current-harmonics generated by nonlinearities in the current-voltage characteristics that could saturate the current preamplifier at low junction impedances or high gains. The strict phase relationship between a cosinusoidal excitation voltage and the current-harmonics allows excellent cancellation using the displacement-current of a driven compensating capacitor placed at the input of the preamplifier. Removal of DC currents has no effect on, and removal of the first harmonic only leads to a rigid shift in conductivity that can be numerically reversed by adding the known removal current. Our method requires no permanent change of the hardware but only two phase synchronized voltage sources and a multi-frequency lock-in amplifier to enable high dynamic range spectroscopy and imaging.