Surface Vacancy Generation by STM Tunneling Electrons in the Presence of Indigo Molecules on Cu(111)

TL;DR

This study explores how local voltage pulses from an STM affect indigo molecules on Cu(111), revealing surface vacancy creation and atomic restructuring through combined experimental and theoretical analysis.

Contribution

It demonstrates that STM voltage pulses can induce irreversible surface vacancies beneath indigo molecules, supported by density-functional theory calculations.

Findings

Voltage pulses cause irreversible modifications to molecules and surface structure.

Surface vacancies of copper atoms are created beneath indigo molecules.

Indigo oxygens stabilize copper adatoms, oxidizing them.

Abstract

Herein, we invesgate the consequence of local voltage pulses on the adsorption state of single indigo molecules on the Cu(111) surface as well as on the atomic structure underneath the molecule. With a scanning tunneling microscope, at 5 K, intact molecules are imaged as two lobes corresponding to the electron density of each indoxyl moiety of the molecule which are connected by a carbon double bond. Then, two short successive voltage pulses with the tip placed above the molecule generate irreversible modifications, as revealed by consecutive scanning tunneling microscopy (STM) imaging. Density-functional theory calculations coupled to STM image calculations indicate the creation of a double surface vacancy of copper surface atoms below the oxygen atom of the indigo molecule as the most plausible scenario. These extracted copper atoms are stabilized as adatoms by the indigo oxygens, oxidizing each copper adatom to 0.32 electron.