Energy dissipation mechanism of femtosecond laser ablation of DLC/Ti/TiN multilayer heterogeneous films

Abstract

Ultra-hard multilayer heterostructured diamond-like carbon (DLC)/Ti/TiN thin films, featured by their unique multi-interfacial architecture and excellent wear resistance integrated with thermal impedance properties, have been developed as composite anti-friction and wear-resistant microfilms for complex working conditions. Femtosecond laser-controlled ablation has emerged as a key technology for precise micro-nano machining of such thin-film materials, with energy dissipation serving as the fundamental mechanism governing controlled ablation. However, the underlying physical mechanisms remain poorly understood. Herein, the femtosecond laser ablation of DLC/Ti/TiN films was investigated via integrated ablation experiments, multi-scale finite element modeling, and advanced characterization techniques (FIB, SEM, EDS), aiming to reveal the energy dissipation dynamics that govern material removal and structural evolution. Firstly, a proposed model simulates the energy transfer characteristics (deposition, absorption, diffusion) during femtosecond laser ablation and calculates the specific electron explosion force. For the first time, the energy distribution ratios among the three dominant interaction mechanisms (thermal conduction, plasma formation, and electron explosion force) are quantified. This quantification unveils their nonlinear dependence on laser energy. Detailed characterizations of inverted conical blind holes and diffusion zones confirm that plasma recoil dominates material ejection, while electron explosion forces drive interfacial delamination. The splashing morphology and crack propagation are correlated with recoil pressure gradients and Coulomb repulsive stress waves, and the redeposited particles at hole openings verify momentum dissipation during axial ejection. Furthermore, non-thermal mechanisms are identified to maintain structural integrity: Raman spectroscopy reveals graphitization of DLC without interfacial delamination, and EDS analysis confirms extremely low oxidation levels, as plasma-dominated material removal limits oxidation. As a result, femtosecond ablation induces only local phase transitions and minimal structural damage in multilayer films. Finally, this research provides a solid theoretical foundation for controlled femtosecond laser micro-nano manufacturing of DLC/Ti/TiN thin films, highlighting the critical role of energy dissipation dynamics in guiding process optimization and material design.