Local spectroscopy and atomic imaging of tunneling current, forces and dissipation on graphite

TL;DR

This study compares atomic imaging and spectroscopy in STM and AFM on graphite, revealing differences in images and dissipation signals that depend on distance and bias, challenging assumptions of their similarity.

Contribution

It demonstrates that STM and AFM images of graphite differ significantly under certain conditions, and provides detailed spectroscopy of tunneling current, frequency shift, and damping signals.

Findings

AFM and STM images differ depending on distance and bias.

Dissipation signal is twice as sensitive to distance as frequency shift.

Spectroscopy reveals distinct behaviors of current, force, and dissipation on graphite.

Abstract

Theory predicts that the currents in scanning tunneling microscopy (STM) and the attractive forces measured in atomic force microscopy (AFM) are directly related. Atomic images obtained in an attractive AFM mode should therefore be redundant because they should be \emph{similar} to STM. Here, we show that while the distance dependence of current and force is similar for graphite, constant-height AFM- and STM images differ substantially depending on distance and bias voltage. We perform spectroscopy of the tunneling current, the frequency shift and the damping signal at high-symmetry lattice sites of the graphite (0001) surface. The dissipation signal is about twice as sensitive to distance as the frequency shift, explained by the Prandtl-Tomlinson model of atomic friction.