Laser-Driven Aerosol Synthesis of Nickel Nanoparticles

Nanoparticles of nickel have been prepared by laser-driven decomposition of nickel carbonyl. In this method, an infrared laser rapidly heats a dilute mixture of nickel carbonyl and a photosensitizer in a carrier gas to decompose the precursor and initiate particle nucleation. To produce nickel nanoparticles, nickel carbonyl was generated in situ from activated nickel powder and CO at room temperature, so that we never maintained any inventory of this highly toxic compound. During the synthesis process, laser heating allows for rapid cooling of the freshly nucleated particles by mixing with unheated gas. By varying the precursor flow rate, laser energy, and unheated gas flow rate to change the residence time, precursor concentration, and reaction temperature, the average particle size can be controlled over a range of primary particle diameters from 5 to 50 nm. The particle size and crystalline structure have been characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM), nitrogen physisorption surface area measurement (the BET method), and X-ray photoelectron spectroscopy (XPS). Results of magnetization measurements for small superparamagnetic nickel nanoparticles (about 8-nm diameter) are also presented.