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

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Abstract
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) substrate by LEED. At 0.12 monolayer (ML) Eu coverage, the (5 × M) superstructure (M > 2) preserved the hBN/Ir(111) Moiré pattern showing unidirectional Eu ordering beneath hBN. At 1.6ML, a (5 × 2) superstructure emerged, where excess Eu atoms diffused into the bulk, adopted a tri-valent state. The alloy formation with Ir results in a small Ir core level shift observed by XPS. At the highest preparation temperature (1/3ML), a (√3 × √3)R30◦ superstructure formed, indicating the formation of EuIr2 surface alloy beneath the hBN, containing di-valent Eu atoms with potential ferromagnetic behavior. Air exposure was used to evaluate the protection of the hBN layer, indicating a partial protection. The hBN layer, remained intact as confirmed by ARPES analysis.

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