Formation and protection of an Eu-Ir surface compound below hexagonal boron nitride

TL;DR

This study investigates Eu intercalation under hBN on Ir(111), revealing various surface structures, a EuIr₂ alloy formation, and the protective role of hBN against air exposure through multiple surface analysis techniques.

Contribution

It provides new insights into Eu intercalation structures, alloy formation, and the protective capabilities of hBN layers on Ir(111) surfaces.

Findings

Different superstructures depend on Eu coverage and temperature.

EuIr₂ alloy forms beneath hBN at high Eu coverage.

hBN layer partially protects EuIr₂ alloy from air exposure.

Abstract

Europium (Eu) intercalation below hexagonal boron nitride (hBN) on an Ir(111) substrate at various Eu coverages is investigated. The structural and electronic properties were examined using low energy electron diffraction (LEED), scanning tunnelling microscopy (STM), x-ray photoelectron spectroscopy (XPS) and angle-resolved photoemission spectroscopy (ARPES). Depending on the deposition temperature, different superstructures, (5 $\times$ $M$), (5 $\times$ 2), and ($ \sqrt{3}$ $\times$ $\sqrt{3})R30^{\circ}$ with respect to the Ir substrate were identified by LEED. The (5 $\times$ $M$) superstructure ($M$ $>$ 2), at 0.1 monolayer (ML), preserved the hBN/Ir Moir{\'e} pattern and exhibited a unidirectional ordering of Eu atoms. At higher coverage of 0.26 ML, a (5 $\times$ 2) superstructure emerged, where excess Eu atoms diffused into the bulk and were analyzed as Eu in a tri-valent state. At the highest preparation temperature with a one-third ML Eu, the formation of a ($\sqrt{3}$ $\times$ $\sqrt{3})R30^{\circ}$ superstructure indicates the presence of a EuIr$_{2}$ surface alloy beneath the hBN layer, with di-valent Eu atoms suggesting potential ferromagnetic properties. Air exposure was used to evaluate the protection of the hBN layer, and the results indicate that the EuIr$_{2}$ surface alloy was partially protected. However, the hBN layer remained intact by intercalation and air exposure, as confirmed by ARPES analysis.