# Observations of Isolated Mobile Au–Br and Au–S Surface Complexes on Au(100) Electrodes

## TL;DR

This study uses high-speed scanning tunneling microscopy to observe gold-bromide and gold-sulfur surface complexes on gold electrodes, revealing their stability and movement.

## Contribution

The paper provides the first direct experimental evidence of Au–Br and Au–S surface complexes on Au(100) electrodes.

## Key findings

- Au–Br and Au–S surface complexes form as stable molecular species on Au(100) electrodes.
- These complexes diffuse across the surface and remain stable at negative potentials.
- The complexes are identified as Au2Br6 and Au2S2 based on intramolecular resolution imaging.

## Abstract

Wet‐chemical processing of metals, for example, galvanic deposition, etching, and nanoparticle synthesis, usually requires complexing agents. In particular, for noble metal processing, anionic complexing species, such as halides or sulfide are indispensable. While it is known that these species strongly adsorb on metal surfaces and affect metal nucleation and growth, the detailed role of these anions in the underlying atomistic processes is less clear. Often, it is assumed that surface complexes are involved, but experimental evidence for the latter is still lacking. Here, we present direct in situ video‐rate scanning tunneling microscopy observations of gold–bromide and gold–sulfur surface complexes on Au(100) electrodes. Based on the intramolecular resolution images obtained in these studies, these species can be assigned to a dimeric planar Au2Br6 and a linear Au2S2 complex. Once formed, the surfaces complexes are stable even at rather negative potentials and diffuse as molecular species on the Au surface.

Fast scanning tunneling microscopy measurements reveal the formation of Au–Br and Au–S surface complexes on Au(100) electrodes in aqueous electrolytes. These complexes are stable and diffuse as molecular entities over the Au surface, demonstrating that surface transport via complexes has to be considered in wet‐chemical growth and dissolution processes.