Ordered Carbohydrate-Derived Porous Carbons

Ordered Carbohydrate-Derived Porous Carbon

Nano- and Submicrometer-Sized Spherical Particle Fabrication Using a Submicroscopic Droplet Formed Using Selective Laser Heating

Detailed characterization of products by pulsed laser melting in liquid was performed for TiO₂ particles obtained at different laser fluences. The size, crystal structure, and inner structure of obtained spherical particles depended on the irradiating laser fluence. Single crystalline submicrometer spherical TiO₂ particles of 200 nm were obtained using nanosecond pulsed laser irradiation at 100 mJ cm^–2 pulse^–1 onto raw particles dispersed in ethanol using cross-sectional high-resolution transmission electron microscopy observation. At higher laser fluence (e.g., 225 mJ cm^–2 pulse^–1), large submicrometer spheres with strain and twin structures 500 nm in diameter and nanometer spheres of 70 nm were simultaneously observed. The formation of such bimodal size distribution of obtained particles was explained based on the phase transition fluence curves deduced by Mie theory and the optical absorption increase induced by the formation of nonstoichiometric TiO₂ particles. Thus, with the appropriate laser fluence, this laser process can produce single crystalline submicrometer spherical particles and nanometer spheres via cooling of droplets formed by a selective laser heating by optical absorption