Morphological, elemental and hardness analysis of femtosecond laser irradiated Al targets

Abstract

Aluminum (Al) samples were irradiated with femtosecond (fs) laser pulses for different laser fluences under two different environments of vacuum & Oxygen (O2). Nano/Micro structures on the surface of irradiated Al were explored by using Scanning Electron Microscope (SEM). Self-organized patterns like ripples, cellular structures, cluster of particles and cavities are observed by SEM analysis. Single and multiple (100) shot, ablation threshold value and incubation coefficient were also calculated by means of SEM images, under both ambient conditions i.e. vacuum and O2 environments. While the comparison for single and multiple (100) shots shows a decrease in the value of ablation threshold with increase of number of laser pulses due to presence of incubation effect. X-ray Diffraction (XRD) and Energy Dispersive X-ray Spectroscopy (EDX) analysis were utilized for identification of phases and the chemical composition of ablated targets, respectively. A variation in Al content as well as in peak intensities of almost all phases is observed under vacuum treatment. In case of treatment in O2 ambient, oxides of Al are achieved with significantly enhanced concentration of O2. After ablation under vacuum condition reduction in atomic O content (already present on un-ablated target) is observed. The reduced ablation threshold of metals makes the laser material processing mechanisms like cutting, drilling, welding and surface modifications, more effective. The observed reduced ablation threshold of Al in O2 as compared to vacuum, as well as oxidation of Al along with the growth of surface structures make this metal more useful for various industrial as well as scientific applications. Nano-hardness measurement shows an increase in nanohardness of irradiated targets as compared to un-irradiated ones with the increase of fluence under both ambient conditions.