Laser pyrolysis for controlled morphing and chemical modification on 3D microlattices

Abstract

3D microlattices fabricated through multi-photon lithography have been widely utilized for photonics, bio-scaffolds and architected metamaterials. Post-processing techniques have accentuated the reduction of the overall size to the nanoscale and the modification of the material properties of these structures. However, there are no processing techniques that can locally modify the morphology and the properties of microscale polymeric structures. In this study, our objective is to demonstrate localized nanoscale morphing and material modification of polymer 3D lattice structures through continuous wave laser induced selective pyrolysis, leading to local carbonization. Our approach of focused laser heating on single beam members precipitates thickness reduction from 500 nm to 250 nm. Local size reduction can further embrace collective mechanical deformation and form new complex geometries. Through spatially-variant laser heating on the periodic structures, curved and gradient three-dimensional shapes can be fabricated. Finite element analysis explained the resulted changes and predicted the enhanced mechanical performance. Ultimately, in situ scanning electron microscopy of the microindentation process proves that the modified structure demonstrates a substantially improved mechanical performance through the combination of high strength and ductility of the ceramic and polymer counterparts. Our findings and main results demonstrate the significance of the laser as a vital tool to ameliorate the geometrical complexity and material heterogeneity for enhanced mechanical performance.