Thickness dependence of microstructure and properties in Be2C coatings as a promising ablation material

Abstract

Beryllium carbide (Be2C) thin films have proven to be promising ablation materials, but the properties of Be2C coatings of the greater thickness required for inertial confinement fusion capsules are still unknown. In this work, Be2C coatings of various thicknesses (0.3–32.9 µm) are prepared by DC reactive magnetron sputtering. The influence of thickness on crystal properties, microstructure, and optical properties is investigated. The results indicate that the crystallinity of polycrystalline Be2C films improves with increasing thickness, while the grain size (∼5 nm) and texture properties (without a preferred orientation) have only a weak dependence on thickness. A uniform featureless microstructure and smooth surface (root mean square roughness ∼8 nm) are observed even in thick (32.9 µm) films, despite the presence of defects induced by contaminants. High densities (2.19–2.31 g/cm3) and high deposition rates (∼270 nm/h) are realized, with the latter corresponding to the upper limit for the fabrication of Be2C coatings by magnetron sputtering. The transmittance of the films in the near-infrared region remains at a high level (>80%) and has only a weak dependence on thickness, while the transmittance in the visible region decreases with increasing thickness. In addition, the optical bandgap is estimated to be about 1.9 eV and decreases with increasing thickness owing to the presence of defects.