Direct Growth of Polycrystalline Diamond on Untreated CaGdAlO4 Crystal via MPCVD

Insulating oxide substrates require complicated pre-seeding or bias-enhanced nucleation to realize diamond deposition, which introduces defects and extra costs, while binary metal oxides are limited by fixed compositions and severe lattice/thermal mismatches with diamond. In this study, we identify CaGdAlO4 (CALGO) as a novel substrate candidate with layered tetragonal structure, rare-earth catalytic activity, low lattice mismatch (2.7%) with diamond and outstanding thermal stability.

Nevertheless, the feasibility of direct diamond deposition on CALGO and its surface-dependent nucleation mechanism remain poorly understood. Herein, continuous polycrystalline diamond films were directly deposited on untreated (001), (100) and (110) CALGO crystals via microwave plasma chemical vapour deposition (MPCVD), and characterized the nucleation density and quality. The surface energy and CH3 radical adsorption affinity of different CALGO surfaces were quantitatively analyzed by first-principles calculations. The polar (001) surface has the highest surface energy but weak CH3 adsorption, yielding poor diamond crystallinity.