title: Laser fragmentation of water-suspended gold flakes via spherical submicroparticles to fine nanoparticles.
abstract: By nanosecond, 532-nm laser irradiation typically at approximately 1 J/(cm2 pulse), water-suspended thin gold flakes, 0.1-0.2-microm thick but more than 10-microm across, were efficiently fragmented in a unique two-step mode, as evidenced by the in situ extinction spectra taken as a function of the laser irradiation time. The initial main photoproducts were spherical gold particles in the submicrometer regime. Their ensuing laser fragmentation in oxygen-free water environment generated stable, negatively charged, fine nanoparticles less than 10 nm in diameter, characterized by a considerably weak and blue-shifted plasmon band. The Mie theory can reproduce these distinct spectral features of the fine nanoparticles as well as the scattering-dominated extinction spectra of the submicroparticles. The submicroparticle to nanoparticle conversion seemed most likely to be a single-pulse event, not leaving any larger intermediate nanoparticles in the suspension. Oxygen, as an effective electron acceptor, strongly affected the stability of the negatively charged nanoparticles, promoting their quasi-reversible or irreversible agglomeration. From the estimated balance between the absorbed laser energy and the energies for the relevant particles to produce a high-temperature molten state, possible fragmentation mechanisms are discussed.
authors.affiliation: Department of Molecular Engineering, Graduate School of Engineering, Kyoto University, Katsura, Kyoto 615-8510, Japan. Kawasaki@ap6.kuic.kyoto-u.ac.jp
authors.forename: Mitsuo
authors.initials: M
authors.lastname: Kawasaki
authors.forename: Kazuhisa
authors.initials: K
authors.lastname: Masuda
mesh_terms: D000465:Algorithms; D006046:Gold / Q000528:radiation effects*; D007834:Lasers; D017348:Microscopy, Electron, Scanning Transmission; D053758:Nanoparticles / Q000528:radiation effects*; D010100:Oxygen / Q000737:chemistry; D010316:Particle Size; D013535:Suspensions; D014867:Water
chemical_list: D013535:Suspensions; D014867:Water; D006046:Gold; D010100:Oxygen