Electron paramagnetic resonance of alkali metal atoms and dimers on ultrathin MgO

TL;DR

This study combines electron paramagnetic resonance with scanning tunneling microscopy to investigate the magnetic and charge properties of alkali metal atoms and dimers on ultrathin MgO, revealing their charge states and magnetic moments.

Contribution

It demonstrates a novel application of EPR-STM to probe the bonding and charge states of alkali metal dopants on ultrathin oxide layers, advancing surface and nanodevice analysis.

Findings

Li₂, LiNa, and Na₂ dimers exhibit magnetic moments of 1μ_B, indicating spin radicals.

Single alkali atoms have no magnetic moment and a +1e charge state.

Charge transfer to the metal substrate causes ionization of the adsorbates.

Abstract

Electron paramagnetic resonance (EPR) can provide unique insight into the chemical structure and magnetic properties of dopants in oxide and semiconducting materials that are of interest for applications in electronics, catalysis, and quantum sensing. Here, we demonstrate that EPR in combination with scanning tunneling microscopy (STM) allows for probing the bonding and charge state of alkali metal atoms on an ultrathin magnesium oxide layer on a Ag substrate. We observe a magnetic moment of $1\mu_\mathrm{B}$ for Li$_2$, LiNa, and Na$_2$ dimers corresponding to spin radicals with a charge state of $+1e$. Single alkali atoms have the same charge state and no magnetic moment. The ionization of the adsorbates is attributed to charge transfer through the oxide to the metal substrate. Our work highlights the potential of EPR-STM to provide insight into dopant atoms that are relevant for the control of the electrical properties of surfaces and nanodevices.