Real-Time Imaging of K atoms on Graphite: Interactions and Diffusion

TL;DR

This study uses low-temperature STM to image potassium atoms on graphite, revealing their interactions, diffusion behavior, and dipole moments through experimental imaging and simulations.

Contribution

It provides the first direct imaging of K atom interactions and diffusion on graphite, quantifies the dipole moment, and measures the energy barrier for atom hopping.

Findings

Potassium atoms exhibit repulsive interactions on graphite.

The dipole moment of a single K atom is 10.5 Debye.

The energy barrier for diffusion is 32 meV.

Abstract

Scanning tunneling microscopy (STM) at liquid helium temperature is used to image potassium adsorbed on graphite at low coverage (~0.02 monolayer). Single atoms appear as protrusions on STM topographs. A statistical analysis of the position of the atoms demonstrates repulsion between adsorbates, which is quantified by comparison with molecular dynamics simulations. This gives access to the dipole moment of a single adsorbate, found to be 10.5 Debye. Time lapse imaging shows that long range order is broken by thermally activated diffusion, with a 32 meV barrier to hopping between graphite lattice sites.