Search

Graphite-based metal transition-layer substrates hold great potential for preparing large-area diamond films and achieving crack-free release. In this study, a five-inch crack-free free-standing diamond film was prepared on a graphite substrate with a sacrificial Mo/Ti double-layer transition layer using direct-current arc plasma jet chemical vapor deposition (DC jet CVD). The interfacial bonding and diffusion behavior between the diamond and the transition layers were investigated. The effect of abundant metal particles and elemental diffusion between layers on film adhesion and stress release are discussed and analyzed. The surface of Ti layer prepared by the multi-arc ion-plating contains numerous metal particles that provide a template for the fine-crystalline Mo layer. Metal particles are encapsulated and embedded in the diamond and act as anchors that ensure the stability of the substrate–diamond bond during high-temperature deposition. After deposition, those metal particles act as weak points and play crucial stress-release roles. Mutual elemental diffusion occurs between the Ti, Mo, and diamond layers. Ti penetrates the Mo layer to form a continuous 140-nm-thick thin layer during the initial deposition period, facilitating diamond nucleation. Carbon from the plasma and diamond diffuses into the metal transition layer. Thermal stress generated between the diamond and the graphite substrate is released by destroying the metal transition layer with high thermal expansion coefficient and low elastic modulus during cooling from the deposition temperature. Cracks rapidly propagate along the interface between destroyable transition layers and graphite substrate, which results in the liftoff of a fully crack-free diamond film. [Display omitted] [ABSTRACT FROM AUTHOR]

Deposition of a consistent diamond coating on intricate surfaces has historically posed a difficulty. This article presents the advancement in research on depositing a uniform diamond coating on three-dimensional (3D) silicon spheres, utilizing a faraday cage within a microwave plasma chemical vapor deposition (MPCVD) reactor. A self-consistent three-dimensional multi-physics field model has been established for simulating the microwave electric field and plasma inside a reactor with or without a faraday cage. Results indicate the cage effectively reduces the discharge at the top of the silicon sphere and improves uniformity of the distribution of the microwave electric field and plasma electron density on the sphere's surface. MPCVD trials have demonstrated that a powerful discharge takes place at the apex of the silicon sphere resulting in an excessive thermal gradient if the cage is not added. The apex of the silicon sphere is covered with a blend of diamond and graphite phases. Due to the excessive internal stress of the coating, approximately 50 % of the samples experience coating detachment. After the addition of the cage, the strong discharge is transferred to the top of the cage, effectively suppressing the microwave electric field and plasma inside the cage. Improved quality, reduced internal stress, and enhanced uniformity of the polycrystalline diamond coating are achievable on the silicon spheres within the cage. Moreover, this technique offers a novel approach to coat diamond on complex 3D geometries. [Display omitted] • Three-dimensional multi-physics modeling verifies that faraday cage suppresses microwave electric field and plasma. • The Faraday cage improves the uniformity of the distribution of microwave electric fields and plasma in the internal space. • Uniform, high crystal quality, low stress diamond coating. [ABSTRACT FROM AUTHOR]