3. Results and discussion
The low-resolution transmission electron micrographs of the graphene-carbon nanotube hybrid material are illustrated in Figure 1 for the production of fiber-reinforced polymer composites. From a mechanical point of view, carbon nanotubes exhibit excellent rigidity, comparable to steel, while being extremely light. In addition, they exhibit excellent electrical and thermal conductivity properties which make it possible to envisage using them as additives to confer these properties on various, particularly macromolecular, materials such as polyamides, polycarbonate, polyesters, polystyrene, and polyethyleneimine, as well as other thermoplastic and thermoset polymers. Carbon-based materials are widely used due to their mechanical and chemical stability, excellent intrinsic electrical conductivity, and large surface area. Graphene-carbon nanotube multi-stack three-dimensional architectures can overcome the limitations and restricted performance typically encountered with carbon-based materials by using the combined strategies of three-dimensional architecture and low-dimensional carbon nanomaterial characteristics. Such graphene-carbon nanotube stacks have one or more of the following characteristics: graphene and carbon nanotubes are active materials that have unique electrical properties, particularly high surface area and high electrical conductivity, the carbon nanotube array of the graphene- carbon nanotube stack acts as a spacer to prevent graphene self-aggregation, maintaining a large active surface area, and stable electrical and mechanical contact is generated between carbon nanotube and graphene due to the direct growth of carbon nanotube between the graphene layers. A graphene-carbon nanotube stack may be fabricated by sequentially developing a stack of alternating graphene and catalytic metal layers, breaking down the metal layers into catalytic nanoparticles, and causing the simultaneous growth of the carbon nanotube between the graphene layers at the sites of the catalytic nanoparticles and the expansion of the graphene-carbon nanotube stack. The growth tube furnace chemical vapor deposition method is adapted to grow graphene. Graphene synthesis begins when the carbon feedstock is introduced into the furnace tube, where it thermally decomposes into carbon and hydrogen radicals in the presence of the catalyst. In the case of copper, growth is limited to the surface of the metal. The dissociated carbon species diffuse across the surface of the metal, where they nucleate as seeds which grow and coalesce to form a continuous graphene film.