Preparation method of self-supporting ultrathin diamond film

The invention discloses a preparation method of a self-supporting ultrathin diamond film, and belongs to the technical field of diamond self-supporting film growth. The method comprises the followingprocess steps: a, taking a polished diamond film with the surface roughness of less than 30nm as a substrate, depositing an ultra-nano diamond thin layer of 100 to 3000nm on the surface of the substrate by a chemical vapor deposition method, and introducing a high-concentration carbon source to construct a carbon-carbon bond network layer, thereby being beneficial to nucleation and growth of an epitaxial diamond film and realizing growth of a high-quality epitaxial layer; b, growing a polycrystalline diamond film with the thickness of 10 to 300 [mu]m on the surface of the substrate in a homoepitaxy mode, and grinding and polishing the surface of the substrate according to requirements after deposition is finished; c, carrying out heat treatment on the polycrystalline diamond film to form adisordered graphite struc