| Finding out the processes of the microcosmic reactions and particle states in the early growth of BaTiO3 (BTO) thin films is very important for the preparation and control of good structure in the growth of BTO thin films. The precedence reacton processed of Ba, Ti, and O atoms, the formation of BaO and TiO2 molecules, and the microcosmic reaction mechanism underlying the formation of BTO, the BaO and TiO2 molecules adsorption on Si(001) surface have been investigated using a generalized gradient approximation of density functional theory (DFT) at the PE91/DNP level. And the DMol3 and CASTEP package of Materials Studio 4.0 are used for the calculations.It was found that BaO, TiO2, and BTO molecules are the primary particle states in the early growth of BTO thin films. As it acts as a combining center, the TiO2 molecule is preferentially formed. Subsequently, BaO molecules combin with this center and then BTO molecule, which is stable and somewhat similar to the BTO unit cell, is constructed. Due to the mechanisms, BTO thin films have been formed.The theoretical study of BaO and TiO2 molecules adsorption on Si(001) surface has been investigated using ab initio molecular dynamics method. We also have found the trajectory and energy of every moment in the process. At the time, the adsorption energys of corresponding stage has been calculated.By comparison the adsorption energy, we concluded that TiO2 molecule have been adsorbed growth priority than SrO molecule on the Si(001) surface.while TiO2 molecule have been adsorbed growth priority than SrO molecule on the SrO-SrTiO3(100) surface. In this instance, SrO and TiO2 layer are growth alternating layered cycle. The results are well in accordance with experimental.At the same time, the bonding process of SrO molecule on the TiO2-SrTiO3(100) surface have been investigated by using Mulliken, highest occupied and lowest unoccupied molecular orbital theory and density of states. Consistent with the results of kinetic studies, it indicated that Sr atoms in SrO molecule combine with O atoms in the surface priority. And then O atoms in SrO molecule combine with Ti in the surface, Sr-O bond was broken in SrO molecule.The bonding process of TiO2 molecule on the SrO-SrTiO3(100) surface has been investigated by the same method. Ti atoms in TiO2 molecule combine with O atoms in the surface combine first, and then O atoms in TiO2 molecule combine with Sr atoms in the surface.We can see that the final configurations of SrO molecule on the TiO2-SrTiO3(100) and TiO2 molecule on the SrO-SrTiO3(100) surface are similar with structure of SrTiO3 unit cell. It confirms that the model of SrTiO3 early growth is migration of unit cell and layer growth. In addition, the chemical bond of TiO2 and BaO molecules in the adsorption process of Si-based was analyzed respectively by using the Mulliken charge distribution and frontier orbital theory. It was found that in the adsorption process of BaO molecules, O atoms was connected with the Si atoms located on the surface of the substrate. Then Ba-O bond was broken; at the same time, the Si atom first was combined with one O atom, and then combined with the Ti atom, to form a stable Ti-centered tetrahedral structure, which are consistent with the dynamics.Finally, for BTO molecules in the adsorption process based on Si-based molecular, by using the BTO formation mechanism, and comparative analysis of BaO and TiO2 molecular adsorption process, it can be concluded that the Si atoms was first connected with the two O atomics which comes from the BTO, and then combined with the Ti atoms, while the remaining elements of a O atom will be influenced by the lone electron pairs near the Ba atom ro form a stable structure which is similar to the diamond.
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