Ultra-strong carbon fibers via atomic layer deposition-induced dual-scale defect regulation

Carbon fibers (CFs) with high tensile strength are highly desirable as reinforcement materials in advanced composites. However, their theoretical tensile strength (∼180 GPa), estimated from sp 2 C-C bond strength in defect-free structures, remains unattainable because of intrinsic surface and internal defects. Here, we demonstrate an atomic layer deposition (ALD)-based strategy enabling dual-scale defect mitigation in commercial polyacrylonitrile-based CFs through simultaneous surface passivation and internal structural reinforcement. Conformal Al 2 O 3 layers reduced surface irregularities and stress concentration sites, while infiltrated Al-containing species promoted interfacial bonding and cross-linking within the carbon microstructure. Consequently, the tensile strength of commercial CFs was significantly enhanced after ALD treatment, with T1000G fibers exhibiting a ∼41% increase in tensile strength and reaching 8.45 ± 1.35 GPa. Structural analyses using X-ray diffraction, Raman spectroscopy, small-angle X-ray scattering, field‑emission transmission electron microscope, and Energy-dispersive X-ray spectroscopy mapping revealed reduced microvoid dimensions without significant alteration of the graphitic microstructure. These findings establish ALD-induced dual-scale defect mitigation as an effective and potentially industrially applicable approach for producing next-generation ultra-strong CFs.