HyoSook Lee

Effect of surfactants on the size and shape of cobalt nanoparticles synthesized by thermal decomposition

Cobalt nanoparticles with various morphologies were synthesized by thermal decomposition of cobalt acetate in the presence of various surfactants at 260°C. A combination of surfactants consisting of sufficient amount of oleic acid together with polyvinylpyrrolidone and oleylamine resulted in well-dispersed cubic cobalt nanoparticles of ∼25nm in average size. When 1,2-dodecanediol was added as a reducing agent to the surfactant mixture, triangular-prism-shaped nanoparticles of ∼50nm in average size were synthesized. Furthermore, an injection of trioctylphosphine into the reactor as an additional surfactant decreased the particle size to ∼10nm. The XRD pattern of the prism-like particles corresponded to hexagonal close-packed crystalline phase of cobalt.

Preparation of Monodispersed Iron Nanoparticles by Thermal Decomposition

Abstract Monodispersed iron nanoparticles were prepared by thermal decomposition of iron carbonyl at low temperatures of 160–180 °C in kerosene. The iron nanoparticles were spherical and their average size was decreased from 11.2 nm to 8.6 nm with increasing decomposition temperatures in the range of 160 °C to 180 °C. The as-prepared iron nanoparticles were amorphous, but the surface of the particles was easily oxidized to be spinel structured.

Characteristics of laser-produced plasmas in a gas filled chamber and in a gas jet by using a long pulse laser

The dynamics of the laser-produced plasma in a gas filled chamber and in a gas jet were investigated using a relatively low intensity laser (I⩽5×1012 W/cm2) with long pulse duration (7 ns). Visualization methods such as the Mach–Zehnder interferometry and the shadow imaging were employed to characterize the shock velocity, electron densities, and temperatures in the laser-produced plasma. The electron density depletion on the laser propagation axis was observed in a gas jet but not in the gas filled chamber. Qualitative analysis for the density depletion is discussed by employing a fluid theory for the ambipolar diffusion of the plasma species. In the gas filled chamber, increase of the laser energy, and applied gas pressure results in faster and further propagation of the shock front with the distance-time relation of Rs∝t2/5, implicating an instantaneous energy release at a point. However, the plasma produced in a gas jet shows a rather linear relation of Rs∝t at early time (t⩽10 ns).

Simulation of Photon Acceleration Using Laser Wake Fields

Numerical simulations of photon acceleration using laser wake fields are presented with one‐ and two‐dimensional electromagnetic particle‐in‐cell codes. Up to 150% of frequency upshift was observed in the one‐dimensional simulation, but around 10% in the two‐dimensional simulation because of laser diffraction as well as transverse plasma motion. The saturation mechanisms of photon acceleration and the effects of slippage, dispersion, diffraction, and pump depletion are discussed for parameter optimization.