Conductivity Enhancement of Multi-walled Carbon Nanotube Films by Ultraviolet Femtosecond Laser Surface Modification

The ultraviolet (UV) femtosecond laser, combining high photon energy with ultrafast energy deposition characteristics, offers a unique pathway for tuning the electrical performance of carbon nanotube films under conditions compatible with flexible substrates. However, systematic investigations into its effects on the modification threshold, microstructural evolution, and surface chemical state of multi-walled carbon nanotubes (MWCNTs) films remain limited. In this work, a UV femtosecond laser was employed for surface modification of MWCNTs conductive films on PET substrates, and the influence of laser parameters on the microstructure and electrical conductivity of the films was systematically examined. By precisely calibrating the modification threshold and ablation threshold, a safe energy window for controllable modification was established, and the optimal processing parameters were identified. Under the optimized conditions, the sheet resistance of the modified films was reduced by 45%, while irreversible structural damage was effectively avoided. Laser treatment induced the formation of periodic wrinkles on the film surface, promoting tight inter-tube adhesion and interfacial fusion. The newly generated carbon layer exhibited a dual-phase feature consisting of ordered graphitic carbon and amorphous carbon, synergistically reducing the inter-tube contact resistance. Concurrently, laser processing achieved simultaneous surface deoxygenation and graphitization of the films. This study establishes the intrinsic relationships among laser parameters, microstructure, and electrical conductivity, providing a theoretical basis and process window for the precisely controlled laser tailoring of high-performance carbon nanotube-based conductive films on polymer substrates.