Growth of nanodiamond/carbon-nanotube composites with hot filament chemical vapor deposition

The growth of diamond/carbon-nanotube (CNT) composites by Hot Filament Assisted Chemical Vapor Deposition (HFCVD) was investigated. The growth was achieved by pre-dispersing commercially available multiwalled CNTs onto a Si(100) surface and subsequently growing diamond nanoparticles over this layer. The diamond/CNT composites were characterized with SEM, TEM, and Raman Spectroscopy. It was found that in a flow of 1% CH₄ in H₂ (a typical condition for microcrystalline diamond growth using HFCVD) most of the CNTs are destroyed by the harsh growth conditions. Reduction in the etching of the CNTs was achieved by reducing the H₂ partial pressure in the precursor flow. There exists an optimal between 2-5% of CH₄ in H₂ wherein the CNTs are not destroyed and the resulting diamond film retains a high percentage of its sp³ structure. The TEM analyses showed that nanometer sized diamond particles nucleate on the surface of the CNTs and grow radially outward. The retention of the CNT structure and the direct growth of the diamond on the CNTs, the two factors necessary for good load transfer between a matrix and reinforcement, suggest the possibility of using this material as a structural composite. Based on the characterization of the composite, a growth mechanism for diamond onto the CNTs was proposed.