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SiO2 nanoporous films have recently gained significant popularity as low-k dielectric constant insulating films. In this study, we demonstrated the fabrication of a low-k SiO2 nanoporous film consisting of SiO2 nanoparticles by pulsed laser deposition. However, to optimize the growth conditions of nanoporous films, it is important to understand the spatial and size distribution of nanoparticles produced by laser ablation. Here, we visualized laser-ablated SiO2 nanoparticles using a two-dimensional laser scattering imaging technique and investigated the influence of gas species and pressure on the spatial distribution of the nanoparticles in the gas phase. After the decay of the plasma emission within several microseconds, a spherical-shaped scattering image depicting the spatial distribution of SiO2 nanoparticles was obtained from a delay time of approximately 10 ms. In Ar gas, the sphericalshaped distribution of SiO2 nanoparticles changed to an ellipsoidal shape with increasing pressure, whereas in O2 gas, it changed a mushroom-like shape. These results show that the gas species and pressure are dominant parameters affecting the spatial distribution of nanoparticle formation. [ABSTRACT FROM AUTHOR]

We have succeeded in growing the ZnO spherical microcrystals by a simple laser ablation in air, and we have obtained ultraviolet (UV) whispering-gallery-mode (WGM) lasing from the sphere under pulsed laser excitation. In this growth technique, a solid ZnO target is rapidly heated by laserinduced plasma, and melted target is splashed from the irradiated spot as droplets. Then, the droplets are crystallized into spherical shapes by the surface tension during the dropping process. This rapid melting and solidifying process may be effective for doping impurities into ZnO. In this study, we fabricated P-, Sb-, and Mg-doped ZnO microspheres, and investigated their structures and optical properties. A blue-shift of UV WGM lasing from Mg-doped ZnO microsphere was obtained, indicating that the band-gap engineering of ZnO microsphere grown by the simple ablation technique was achieved. [ABSTRACT FROM AUTHOR]

We have succeeded in synthesizing ZnO nano/microspheres by a simple laser ablation method in the air and demonstrated whispering-gallery-mode (WGM) lasing from the ZnO sphere excited by a pulsed-ultraviolet laser beam. The spheres with diameters of up to 10μm were simply prepared by laser ablation of a ZnO sintered target by a Q-switched Nd:YAG laser in the air. In this study, we succeeded synthesizing large microspheres with diameters of larger than 20μm by the Nd:YAG laser without Q-switching. The mode spacing of the large sphere was in good agreement with the WGM theory. [ABSTRACT FROM AUTHOR]