Synthesis Of Various Pbs Nanostructures By Pulsed Laser Ablation In Liquids

Compared to other methods for nanomaterial synthesis, laser ablation technique is widely used since it is facile and environmentally-friendly. The mechanism of laser ablation in liquid is different from that of ablation in gas due to the confinement effect of the liquid media. As a narrow direct band gap semiconductor, PbS nanomaterials with strong quantum confinement effect can be easily achieved. In this thesis, different PbS nanostructures were synthesized by laser ablation in liquid and the formation mechanisms of the products were investigated.Self-assembled PbS quantum dots (PbS QDs) were synthesized when Pb target was ablated by pulse laser in dodecyl mercaptan with high-frequency laser or with repeated laser ablations. We found that laser frequency was not the main reason for the formation of PbS QDs and we infered that the QDs formed due to the selective absorption of infrared laser energy by nanoparticles with different size, namely, large nanocrystals absorbed laser energy and got smaller, but small nanocrystals could not absorb laser energy and stayed unchanged. Dodecyl mercaptan not only provided sulfur, but also acted as a stabilizing agent. The as prepared nanocrystals gave photoluminescence in the near-infrared light region.PbS hollow structures were obtained in the case of laser ablation Pb target in mercaptoacetic acid with different pulse widths and frequencies, induced by Kirkendall effect. Products obtained at different time indicated the evolving process of Kirkendall effect.Other PbS nanostructures were also synthesized, inclucing PbS nanocrystals, Pb / PbS heterostructure, Pb@PbS core-shell structure, and PbS nanocrystals, for mixed solution of dodecyl mercaptan and n-hexane with different volume ratio, which is in accord with the Pb-S equilibrium phase diagram. In addition, we synthesized PbS cubes in mercaptoacetic acid, PbS nanocrystals in thiophene, single crystal nanowires with repeated laser ablation in mercaptoacetic acid, assembled nanowires in mixed solvent of dodecyl mercaptan and n-hexane with volume ratio of 5:1. The formation mechanisms of different PbS structures need further study.