Geometric optimizations and calculations of GdGa<sub>7</sub>N<sub>8</sub> cluster were performed by a DMoL program using spin-polarized density functional theory (DFT). The binding energy, HOMO-LUMO gap, Mulliken charge and bonding characteristics were computed and analyzed. It is found that the Gadolinium substituting the Gallium would make the bonds between itself and neighboring atoms longer than that of the undoped cluster. The magnetic moment of GdGa<sub>7</sub>N<sub>8</sub> was found to be 7 <i>μ</i>B. And most of the magnetic moment was focused on the Gd atom owing to its half-filled <i>4f</i>-shell.
Relations between composition and structural and stable properties of cubic zinc selenide-silicon core-shell nanowires (NWs) are studied by first principles calculation. The diameter is between 1.1 and 2.7 nm, and the direction of the NWs considered is . The lattice constants of the nanowires deviate from the Vegard’s law positively with compressed ZnSe core. Stability of the NWs is discussed by taking binding energy into account. Pure Si NWs show an increasing trend of binding energy as the diameter increases while ZnSe NWs do not. Further analysis shows that zinc blende ZnSe NWs might be unstable under small diameters and a phase transition to wurtzite structure would occur. Our findings might give some guidance for the application of ZnSe/Si core-shell NWs in photoelectronics.
The single vacancy, the interstitial atom and the substitution atom are the point defects existing in the semiconductors mainly. The geometry and the effect of point defects on the electronic property of the silicon nanowire (SiNW) were theoretically studied in this work. The energy calculation showed that the substitution-vacancy pair was an energetically favored defect formed in SiNWs. Moreover, from the electronic band structures it was found that, the coupling between a substitution atom and a vacancy takes place at a long distance. The formation of a substitution-vacancy pair results in an energy shift of the bands and the vanishment of the donor level of the doped SiNW. So, the existence of a single vacancy takes great effect on the manufacture of the doped SiNWs.
Zinc blende ZnSe longitudinal twinning nanowires (Type I) and a sandwich structure with the wurtzite ZnSe inserting into the zinc blende ZnSe longitudinal twinning nanowires (Type II) are fabricated via a simple thermal evaporation method. The growth of them might be caused by the crystal plane slip during the phase transformation process from wurtzite ZnSe to zinc blende ZnSe nanowire. The wurtzite ZnSe might have two origins: 1) The phase transformed wurtzite from zinc blende. At first, during the temperature rising stage in the experiment, before the temperature approached to the transformation temperature (T<sub>tr</sub>), ZnSe in zinc blende phase might begin to nucleate and grow. Once the temperature is higher than T<sub>tr</sub>, the zinc blende products would transform to wurtzite phase. 2) The new-born nuclei grown wurtzite phase at high temperature for it is reported that the wurtzite phase is more stable at higher temperature. During the cooling period, the source material is exhausted and no more nucleation would occur. Some of the wurtzite products would transform to zinc blende phase when the temperature is lower than T<sub>tr</sub>. During the process, it is reasonable that the ZB phase begins to form from the outer sides of an individual nanowire. Once the process completes, the longitudinal twinning ZB nanowire would be obtained; otherwise, the sandwich-structured nanowire forms.