| Since the graphene was successful prepared in experiment, because of the unique electronic structure and electrical properties, more and more people are interested in 2D layered materials. Since then, some 2D layered materials are prepared in experiment such as silicone germanene and C3N4 film. However, interestingly the recent theory and experiment are show that(0001) ultrathin films of wurtzite(WZ) materials or zinc-blende structure(ZB) surprisingly transform into a stable graphitelike structure, but the stability is limited to thicknesses of only a few atomic layers. Specifically the film thickness is only one atomic layer, some system of atoms are in the same plane layer, such as C, BN and ZnO, While some system of atoms in the two different plane, such as Si and Ge. Starting from structural characteristics, we found that the type of graphite form the planar structure of main sp2 hybridization bond energy and outside layer mainly coupled by van der Waals interaction. But for ZB structure or WZ structure mainly formed by sp3 hybridization bond energy. We can found that it is the key factor for the phase transition is the chemical bonds. For this purpose, we established by the method of tight-binding approximation model combined with the primary principle of a variety of semiconductor hybrid bond energy of sp2 and sp3. And it is used to be describe the structure phase transition of thin film and magnetic induced by local charge. Its key points are as follows:1. The plane structure of graphenelike or the buckle structure of silicene in a monolayer:We calculated the hybrid bond energy of sp2 and sp3, such as C, Si, ZnO, GaN and so on. We found that the hybrid bond energy of sp2 more than sp3 for C, ZnO, GaN, BN and so on, so they tend to form the flat structure. But for Si, Ge, GaAs and ZnSe, the hybrid bond energy of sp2 less than sp3, thus they tend to form the buckling structure. Our calculations suggest that hybrid bond energy is the key factors which determined the architecture.2. The critical thickness of structural transformation:The experimental results show that ZnO is WZ structure when the film thickness is infinite. And it is planar structure of graphitelike when the film thickness for the presence of a few atoms layer thickness. We based on the hybrid bond of sp2 and sp3, found that the difference of hybrid bond energy of sp2 and sp3 is the keys actors of the the critical thickness transformation. Based on sp2 and sp3 hybridized bond energy we succeed get the critical thickness and the first principle methods has carried on the proof. And we found that the more difference of hybrid bond energy of sp2 and sp3, the more critical thickness. Moreover, we also discussed the influence of strain on bond energy and critical thickness which shows the hybrid bond energy of sp2 and sp3 are decrease with the linear relationship. But the difference of hybrid bond energy of sp2 and sp3 are increase gradually. At the same time, the critical thicknesses are increase with the linear relationship.3. Magnetic moment induced by local charge: As we all knowns, the more bond energy, the more ability of bound electron. We firstly calculated the localized magnetic moments induced by cation vacancy in all of Ⅱ-Ⅵ, Ⅲ-Ⅴ and Ⅳ-Ⅳ zinc-blende semiconductors and found that not all of the zinc-blende semiconductors vacancy defect can induce localized magnetic moments. Through the further analysis differential charge density distributions found the more localized electrons, the more localized magnetic moments. Most interestingly, we found when the bond energy is greater than 1.60 ev, the magnetic moments will be induced by cationic vacancy. |
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