Controllabe Synthesis Of Nanostuctures By Millisecond Pulsed Laser

The exploration of new concepts, new methods, new materials, new structures and novel properties is an eternal subject in nanomaterials science. In this thesis, by using millisecond pulsed laser as main source, fundamental issues such as controllable synthesis, dispersion, modification and self-assemble of nanomaterials were investigated from the aspects of methodology, mechanism, structure and property. Critical physical and chemical processes such as nucleation, growth and phase transformation of nanomaterials were studied as well.A large amount of metal nanodroplets can be generated from laser ablation of metal target in liquids. The mechanism of―surface reactions of metal nanodroplets with surrounding liquids‖was then proposed, and diverse nanostructures were controllably synthesized by careful selection of liquid medium and laser parameter which determines the consequences of surface reactions of the metal nanodroplets.Surface reactions of metal nanodroplets with organic media and salt solutions were contrastively studied. In organic media, rapid Kirkendall effect could occur on the surface of some metal nanodroplets, which then resulted in the formation of hollow nanoparticles; in salt solutions, decomposition, partial oxidation and replacement reactions concurred and oxide-metal nano-heterostructures could be formed.Nanoscale replacement reaction mechanisms between laser-induced Mg nanoparticles and noble metal ions were systematically studied. The erosion of solvents and the bonding energy between metal atoms determine the nucleation and growth of nanostructures. The replacement reactions with active metal nanostructures as seeds could be a green and efficient method for the design of various nanostructures.Gravely aggregated detonation nanodiamonds were successfully deaggregated by using selective laser ablation, and monodisperse diamond nanocrystals were obtained. During laser ablation, nanodiamonds could be directly modified by the solvent molecules, surface state of the nanodiamonds could be changed as well, which endowed nanodiamonds with extraordinary photoluminescence and ferromagnetism.Various oxide-metal nano-heterostructures were produced by laser chemistry in liquids; formation mechanism of the nanostructures was investigated. Photoionization of semiconducting nanomaterials and metal ions by infrared laser irradiation could lead to the reduction of metal ions; the as-formed metal atoms could then heterogeneously nucleate on the surface of TiO2 or homogeneously nucleate in solution, depending on the concentration of the metal ions.Growth, crystallization and phase transformation of nanocrystals were investigated by in-situ TEM observation. Under electron beam irradiation,―liqudi-like‖Bi nanodot initially formed after nucleation, which facilitated the mobility of Bi nanodot on the surface of TiO2 nanosphere; the repeated―solid-?liquid-like'-solid‖transformation of Bi nanocrystals took place, from which the nanocrystal became more perfect; Cd nanocrystal could grow and become stable via slow atom diffusion and Oswald ripening; metastable carbon nanoparticles became amorphorous first and then were transformed into carbon nano-onions under electron beam irradiation.