Interaction of carbon nanotubes and diamonds under hot-filament chemical vapor deposition conditions

A composite of CNTs and diamond can be expected to have unique mechanical, electrical and thermal properties due to the synergetic combination of the excellent properties of these two allotropes of carbon. The composite may find applications in various fields that require a combination of good mechanical, thermal, electrical and optical properties such as, wear-resistant coatings, thermal management of integrated chips (ICs), and field emission devices.; This research is devoted to the experimental studies of phase stability of diamond and CNTs under chemical vapor deposition conditions to investigate the possibility of combining these materials to produce a hybrid composite. Growth of the hybrid material is investigated by starting with a pre-existing film of CNTs and subsequently growing diamond on it. The diamond growth phase space is systematically scanned to determine optimal conditions where diamond nucleates on the CNT without destroying it. Various techniques including SEM, TEM, and Micro Raman spectroscopy are used to characterize the hybrid material. A selective window where the diamond directly nucleates on the CNT without destroying the underlying CNT network is identified. Based on the material characterization, a growth mechanism based on etching of CNT at the defective sites to produce sp3 dangling bonds onto which diamond nucleates is proposed. Though a hybrid material is synthesized, the nucleation density of diamond on the CNTs is low and highly non-homogenous.; Improvements to the CNT dispersion in the hybrid material are investigated in order to produce a homogenous material with predictable CNT loading fractions and to probe the low nucleation density of diamond on the CNT. The effect of several dispersion techniques and solvents on CNT surface homogeneity is studied using SEM, and a novel, vacuum drying based approach using CNT/dichlorobenzene dispersions is suggested.; SEM and Raman analysis of the early stage nucleation are used to develop a hypothesis of diamond nucleation enhancement by CNT under HFCVD conditions. It is found that the nucleation takes places by etching of the CNT to create a new carbonaceous surface, onto which diamond nucleates. This mechanism is different from the present understanding of the diamond nucleation enhancement by CNTs.