The Applications Of First-Principle Study In Heterogeneous Nucleation And Growth, Phase Transformation Of Nanoparticles

As a frontier field of nowaday scientifical study, nanotechnology will greatly advance the researches of microelectronics, materials, energy and medicine, while the synthesis and character research about nano materials are the key work. With the development of the study methods, the technology of the computational first principle method based on the density functional theory has been used as an assistant method about nano materials. Compared with the traditional methods, the computational simulation can help to realize the complicated phenomenons about nano materials from microstructure to macrostructure, and this technology will bring a revolution to the nano research. By combining the experiments and computational simulations, this paper will design and perform several computational simulation work to study some special and important phenomenon in practical experiments. We hope to explain and guide our experiments and do some beneficial work in these fields.Fisrt, we studied the heterogeneous nucleation and growth about the synthesis of Fe3O4-CdSe nanoparticles. From the experiments we found that different ligands OA/OAm/NaOL effected the number of CdSe crystal nucleus which grown on the surface of Fe3O4 seeds. When the sphere or cubic Fe3O4 seeds were used, the CdSe growth showed a special priority on the certain location of the cubic seeds:firstly the cubic corners, secondly the cubic edges and thirdly the surfaces; in contrast, no similar phenomenon occurred when sphere seeds were used. We calculated the adsorption capability of OA/OAm/NaOL on Fe3O4 facets and found the adsorption competition between ligands and Cd or Se precursors, which meant the strong adsorption of ligands would embarrass the precursor adsorption. Next through the calculation of crystal lattice mismatch and the adsorption capability of Se precursors on the seeds, we explained the CdSe priority growth on Fe3O4 seeds, and elaborated the whole heterogeneous nucleation and growth from the viewpoint of energy.Second, we focused our attention on the synthesis and phase transition controlling of upconversion NaYF4 nanoparticles. For an easy way to get the hexagonal NaYF4, we tried to use NaOL as the ligand to partly replace OA. We performed the calculations about interactions bwtween OA/NaOL and the cubic NaYF4{100} facet, including the adsorption energy and electronic properties of the absorbed NaYF4{100} facet. We found that the oleate ions would be favored with the Y3+on the surface and this would be possible to change the random Na+or Y3+ occupation on the cubic NaYF4 cation positions. We supposed this process would decrease the energy needed in the cantions rearrangement and lower the energy barrier of phase transition. Through the following experiments, we obtained pure hexagonal NaYF4 nanoparticles of small size and good size distribution under a proper usage of NaOL within 5 min. This part of work gave a reasonable explanation about the mechanism of NaYF4 phase transition.