Laser-induced nanoparticle formation

Abstract

General aspects, such as control of size-distribution, agglomeration/coagulation and material properties are discussed for laser-based generation of nanoparticles. Two model systems are presented, i) laser-assisted chemical vapor deposition (LCVD) of tungsten nanoparticles by H 2 reduction of the excited tungsten fluoride precursor gas (WF6) and ii) laser ablation (LA) of tungsten and carbon targets at atmospheric pressure for W and C nanoparticle formation. Size-distributions of the nanoparticles are determined by electron microscopy (TEM) for the LCVD depositions and in-situ by a differential mobility analyzer and a particle counter for the LA experiments. The tungsten deposition rate is measured by X-ray fluorescence spectroscopy; materials characterization is performed by electron and X-ray diffraction techniques, Raman spectroscopy and X-ray photoelectron spectroscopy. The agglomeration/coagulation for LCVD is followed i) by the size-distribution measurements and ii) by optical emission spectroscopy of the emitted thermal (black-body) radiation of the laser-heated nanoparticles. Additionally, optical spectroscopy of the thermal radiation allows determining the temperature of the laser-heated nanoparticles. During laser ablation the size distributions and the amount of desorbed/ablated material are monitored for different ArF excimer laser parameters (fluence, rep. rate). The main and most important aspects of the presented techniques are compared and discussed.