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

Journal article, 2026

The intercalation of europium (Eu) offers an opportunity to tailor magnetic and electronic properties at interfaces, yet its behavior beneath protective 2D overlayers remains poorly understood. Here, Eu intercalation below a monolayer of hexagonal boron nitride (hBN) on Ir(111) was systematically investigated by varying the Eu deposited amount and substrate temperature. Eu was chosen for its tunable valence state and potential for ferromagnetic ordering. 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). Three superstructures were identified with respect to Ir(111) substrate by LEED: (5 × M) superstructure at 0.12 ML surface coverage, preserving the hBN/Ir(111) Moiré pattern with unidirectional Eu ordering; (5 × 2) superstructure at 0.9 ML where excess Eu adopts a tri-valent state and forms an alloy with Ir; and (3×3)R30° superstructure at the highest preparation temperature and 0.3 ML consistent with 2D surface phase EuIr2 alloy formation with di-valent Eu. The intercalation pathway is attributed to grain boundaries and structural defects in the hBN overlayer, emphasizing hBN quality in controlling intercalation. The protective role of the hBN layer was evaluated by air exposure, resulting in a 20% protection.