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

The intercalation of europium (Eu) below a monolayer of hexagonal boron nitride (hBN) on an Ir(111) was systematically investigated as a function of Eu coverage and substrate temperature. The structural and electronic properties were examined using low-energy electron diffraction (LEED), scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS), and angle-resolved photoemission spectroscopy (ARPES). Depending on Eu coverage and deposition temperature, different superstructures such as (5 × M), (5 × 2) and (√3 × √3)R30° were identified with respect to Ir(111). At low coverage of 0.10 monolayer (ML), the (5 × M) superstructure (M > 2) preserved the hBN/Ir(111) Moiré pattern and showed unidirectional Eu ordering beneath hBN. At 0.26 ML, a (5 × 2) superstructure emerged, where excess Eu diffused into the bulk and adopted a tri-valent state. At the highest preparation temperature (1/3 ML), a (√3 × √3)R30° superstructure formed, indicating the formation of EuIr2 surface alloy beneath the hBN layer, containing di-valent Eu atoms with potential ferromagnetic behavior. Air exposure was used to evaluate the protection of the hBN layer, and the results indicate that the EuIr2 surface alloy was partially protected. However, the hBN layer remained intact by intercalation and air exposure, as confirmed by ARPES analysis.