# Adsorption Sites of Individual Metal Atoms on Ultrathin MgO(100) Films

## TL;DR

This study uses Ca doping and scanning tunneling microscopy to identify adsorption sites of individual metal atoms on ultrathin MgO(100) films, revealing how site preferences depend on film thickness and atom type.

## Contribution

It combines atomic resolution imaging with doping techniques to determine adsorption sites of various metal atoms on MgO films of different thicknesses, providing new insights into surface chemistry.

## Key findings

- Ho atoms prefer O sites on bilayer MgO.
- Au atoms adsorb on bridge sites regardless of thickness.
- Co and Fe atoms favor O sites on MgO films.

## Abstract

We use Ca doping during growth of one and two monolayer thick MgO films on Ag(100) to identify the adsorption sites of individual adatoms with scanning tunneling microscopy. For this we combine atomic resolution images of the bare MgO layer with images of the adsorbates and the substitutional Ca atoms taken at larger tip-sample distance. For Ho atoms, the adsorption sites depend on MgO thickness. On the monolayer, they are distributed on the O and bridge sites according to the abundance of those sites, 1/3 and 2/3 respectively. On the MgO bilayer, Ho atoms populate almost exclusively the O site. A third species adsorbed on Mg is predicted by density functional theory and can be created by atomic manipulation. Au atoms adsorb on the bridge sites for both MgO thicknesses, while Co and Fe atoms prefer the O sites, again for both thickness.