Study of metallic fibrous nanoparticle aggregate produced using femtosecond laser radiation under ambient conditions.

In this study, we report formation of weblike fibrous nanoparticle aggregate due to irradiation of bulk iron, aluminium and titanium samples using femtosecond laser radiation at MHz pulse repetition frequency in air at atmospheric pressure. Electron microscopy analysis revealed that the nanostructure is formed due to aggregation of polycrystalline nanoparticles of the respective constituent materials. The nanoparticle diameter varies between 5 and 40 nm and they are covered with an oxide layer of a few nanometres thick. X-ray diffraction and micro-Raman analysis revealed metallic and oxide phases in the nanostructure. The formation of a nanoparticle aggregate is explained by nucleation and condensation of vapour in the plasma plume and by phase explosion. Moreover the laser interaction time plays a significant role in the generation of nanostructure from bulk metals. This study provides evidence that femtosecond laser irradiation can be an ambient condition physical method for metallic fibrous nanoparticle aggregate generation.