Relaxation and Properties of ZnS 110 Surface

ZnS(llO) surface consists of parallel zigzag chains with equal numbers of zinc and sulphur ions (see Fig. 9.12(a)). It is a charge neutral surface. Relaxation of the ZnS (110) surface has been performed using GGA with CASTER Some pioneering works show that there is a negligible displacement of ions below the second and third atomic layer. Therefore, in relaxation calculation, only the atoms on the first layer of the surface are allowed to move. The surface structure and ionic displacement vectors for the (110) surface are shown in Fig. 9.12(b). Ionic displacements due to surface relaxation are presented in Table 9.5. 

These results suggest that the most significant relaxation of the ZnS (110) surface is a downward displacement of the surface Zn atoms by approximately 0.02 nm. The surface S atoms relax out the surface by about 0.01 nm. The band structure and partial density of state (PDOS) of relaxed ZnS (110) surface are illustrated in Fig. 9.13. The atomic and bond overlap population analysis of ZnS (110) surface is listed in Table 9.6. It shows that the band gap of ZnS (110) surface is 1.5 eV, and it is smaller than that of bulk ZnS. The reason for band gap 

1 -atom on the first layer 2-atom on the second layer. 

The models of the ZnS (110) surface doped with Cu and Fe ions are presented in Fig. 9.14. These models are relaxed using GGA with CASTER The rule of 

The PDOS of the relaxed surface doped with Cu and Fe is presented in Fig. 9.15 and Fig. 9.16 respectively. It can be seen that the valence band of the surface doped with Cu is predominantly composed of Cu (3d) orbital which extends from 0 to -5 eV. This is in excellent agreement with Andrea s XPS studies (1999). There is no obvious gap between the occupied and unoccupied levels. The S (3p) and Zn (4p) orbits are located at the bottom of the conduction band. 

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