Densified Vertically-Aligned Carbon Nanotube Arrays by Chemical Vapor Infiltration

The densification of vertically-aligned carbon nanotube arrays into solid-like coatings is highly desirable for certain applications, including those requiring increased robustness or hardness, protection from oxygen at high temperatures and other damaging ambients, or increased effective thermal conductance. Chemical vapor infiltration (CVI) is a technique that essentially extends the commonly-used chemical vapor deposition process to the filling of networks of pores within a fibrous preform by altering the deposition kinetics toward a mass-transfer limited process. In this study, the CVI technique was utilized for filling the space around carbon nanotubes in vertically-aligned arrays on SiO
₂
substrates with a novel but simple approach. Nanotube growth was conducted using a vapor phase catalyst delivery method in a chemical vapor deposition chamber at 770 degC with a mixture of xylene and ferrocene vapors. Once the nanotube growth had ended, the conditions were altered to initiate the infiltration of carbon-containing species into the nanotube array, resulting in carbon deposition on the nanotubes. The extent of infiltration and location of the remaining porosity was determined using SEM analysis and microbalance measurements, for infiltration times up to 10 hours. The type of C-C bonding within the densified films was elucidated using Raman scattering. Vickers microhardness measurements were made to determine the hardness of carbon-densified nanotube arrays. These studies were largely motivated by the anticipated use of carbon nanotubes for on-chip thermal management on wide bandgap high-power semiconductor devices, optical devices, MEMS structures, and nanoscaled electronics