Formation of aggregated nanoparticle spheres through femtosecond laser surface processing

• DOI: 10.1016/j.apsusc.2017.05.094
• Publication Date: 2017-05-12T18:30:28Z
• Authors: Alfred T. Tsubaki; Mark A. Koten; Michael J. Lucis; Craig Zuhlke; Natale Ianno; Jeffrey E. Shield; Dennis R. Alexander
• Keywords: Femtosecond laser; Core-shell; 570; Nanoparticle aggregates; Laser processing; Onion-like; Computer Engineering; 02 engineering and technology; Electrical and Computer Engineering; 0210 nano-technology; 530

A detailed structural and chemical analysis of a class of self-organized surface structures, termed aggregated nanoparticle spheres (AN-spheres), created using femtosecond laser surface processing (FLSP) on silicon, silicon carbide, and aluminum is reported in this paper. AN-spheres are spherical microstructures that are 20-100 μm in diameter and are composed entirely of nanoparticles produced during femtosecond laser ablation of material. AN-spheres have an onion-like layered morphology resulting from the build-up of nanoparticle layers over multiple passes of the laser beam. The material properties and chemical composition of the AN-spheres are presented in this paper based on scanning electron microscopy (SEM), focused ion beam (FIB) milling, transmission electron microscopy (TEM), and energy dispersive x-ray spectroscopy (EDX) analysis. There is a distinct difference in the density of nanoparticles between concentric rings of the onion-like morphology of the AN-sphere. Layers of high-density form when the laser sinters nanoparticles together and low-density layers form when nanoparticles redeposit while the laser ablates areas surrounding the AN-sphere. The dynamic nature of femtosecond laser ablation creates a variety of nanoparticles that make-up the AN-spheres including Si/C core-shell, nanoparticles that directly fragmented from the base material, nanoparticles with carbon shells that retarded oxidation, and amorphous, fully oxidized nanoparticles.