Hidemi Yoshikawa

Preparation of spherical particles by vibrating orifice technique

Preparation of micrometer-sized spherical particles containing Rhodamine 6G (R6G) has been investigated for the spherical cavity micro-laser. Using phenyl triethoxy silane (PTES) as a starting material, R6G-doped monodisperse spherical particles were prepared by the vibrating orifice technique. Processing consists of two major processes: (1) Hydrolysis and polymerization of PTES and (2) Droplet formation from PTES oligomers by vibrating orifice technique. A cylindrical liquid jet passing through the orifice of 10 and 20 micrometers in diameter breaks up into equal- sized droplets by mechanical vibration. Alcohol solvent of these droplets was evaporated during flying with carrier gas and subsequently solidified in ammonium water trap. For making smooth surface and god shaped particles, control of molecular weight of PTES oligomer was essential. R6G-doped hybrid spherical particles of 4 to 10 micrometers size of cavity structure were successfully obtained. The spherical particles were pumped by a second harmonic pulse of Q- switched Nd:YAG laser and laser emission peaks were observed at wavelengths which correspond to the resonance modes.

Cellular Patterns in Organic-Inorganic Hybrid Film

The formation of cellular patterns, known as “Bénard cell”, was investigated in organic-inorganic hybrid films under various conditions. The cells were observed in undoped-hybrid films, and its origin was attributed to the convection of TiO2 nanoparticles formed in the aging process of the sol. These cells showed the particular properties such as the difference between the center and its surrounding: the center showed a lower refractive index than that of the surrounding, a valley at the center with mountain-like surroundings, and a hydrophobic center and hydrophilic surrounding. How the cell patterns were formed depended on the conditions such as the atmospheric humidity and the gravity. It should be also noted that the cells on a silica glass substrate remained after 1000°C heating.