# High dynamic range scanning tunneling microscopy

## TL;DR

This paper introduces a method to enhance the dynamic range of scanning tunneling microscopes by canceling harmonic distortions in current measurements.

## Contribution

A novel technique using active harmonic cancellation to improve STM performance without hardware modifications.

## Key findings

- Active subtraction of current harmonics increases the STM's dynamic range.
- The method uses phase-synchronized voltage sources and a lock-in amplifier for effective cancellation.
- The approach allows high-gain spectroscopy without hardware changes.

## 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 differential conductance 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.

• Active power filter

• Dynamic range compression

• High gain preamplifier

Image, graphical abstract