CNT coalescence within graphitic fibers through ultraviolet pulsed laser annealing

We studied ultra-rapid thermal annealing using a pulsed excimer laser to heat and promote coalescence of individual single-walled carbon nanotubes (CNTs) within fibers to improve transport properties. Individual CNTs consist of graphene cylinders with electrical (>10,000 MS/m) and thermal (>3,000 W/m•K) conductivities that are significantly higher than metals. CNT fibers consist of bundles of CNTs that are in poor physical contact, resulting in large decreases in conductivity between nanotubes. Recently, furnace annealing up to 1700°C demonstrated that the CNTs within these bundles coalesce to form larger diameter CNTs, however, this process is slow and has a high thermal budget. Instead, we demonstrate that pulsed-laser annealing (PLA) with 248 nm ultraviolet (UV) light can also achieve CNT coalescence within the fibers due to strong UV absorbance by opaque CNTs at a reduced thermal budget. Average CNT diameters within a fiber are determined using Raman spectroscopy, with changes to radial breathing modes specific to CNTs correlating to increases in diameter as a function of PLA conditions. We hypothesize that CNT coalescence within the fibers will decrease the local resistance between adjacent CNTs for electric and thermal transport, thus potentially improving both properties for the entire fiber.