Unraveling Be behavior near the Mo(110) surface: A DFT study of Adsorption, diffusion, and aggregation mechanisms

Abstract

Understanding beryllium (Be) impurity deposition on molybdenum (Mo) surfaces is crucial for advancing Mo's use as first mirrors in tokamak fusion devices. Using first-principles density functional theory (DFT), We systematically investigate the adsorption, diffusion, and aggregation behaviors of Be atoms near the Mo(110) surface. Be atoms preferentially adsorb at Hollow sites on Mo(110) surfaces, with adsorption energies decreasing as Be coverage increases. This trend is driven by enhanced Be–Be binding, which dominates at higher coverages. Be aggregation leads to stable quadrilateral Be clusters, reflecting strong structural orientation. Diffusion studies reveal a preferred Hollow→Bridge→Hollow pathway with a 0.57 eV barrier, while surface-to-subsurface penetration requires overcoming a significantly higher energy barrier of 3.69 eV. Be atoms in the subsurface region preferentially occupy octahedral interstitial sites between atomic layers (OIS2), which results in a higher Be concentration between the Mo atomic layers. The positive binding energy between Be atoms facilitates interlayer nucleation. Subsequently, Beₙ clusters can readily displace Mo atoms, resulting in the formation of vacancy–interstitial pairs. This process may lead to the formation of Be-rich precipitates in this region, potentially causing cracking or exfoliation of the Mo surface atomic layers.