Conformal SiNx Coating on Carbon Nanotubes via Transient UV-Ozone Functionalization and Two-Step Atomic Layer...

A conformal SiNx coating on carbon nanotubes (CNTs) was achieved by combining transient UV-ozone surface functionalization with a two-step atomic layer deposition (ALD) process. UV-ozone treatment gradually increased the defect density of CNTs, with the I_D/I_G ratio increasing from 0.05 for pristine CNTs to 0.25 after 7 min of exposure, while the overall fibrous CNT network remained intact. However, prolonged UV-ozone exposure beyond 10 min led to a sharp increase in the I_D/I_G ratio to 0.46, accompanied by structural degradation of the CNT membrane. Hydroxyl (-OH), epoxy (C-O-C), and carbonyl (C=O) groups were introduced by UV-ozone treatment and were partially removed during subsequent high-temperature processing. Accordingly, direct high-temperature ALD resulted in incomplete SiNx coverage of the CNTs, suggesting insufficient nucleation. A two-step ALD process, consisting of several cycles of low-temperature nucleation at 100 °C followed by high-temperature growth at 700 °C, enabled more conformal deposition of SiNx on CNTs. In addition, both annealing and ALD reduced the defect level toward that of pristine CNTs, supporting the transient nature of UV-ozone-induced functionalization.