Abstract
The Ti-doped Sn O2 (110) surface has been investigated by using first-principles method with a slab model. The geometrical optimizations and band-structure calculations have been performed for four possible doping models. Our results indicate that the substitution of Ti for sixfold-coordinated Sn atom at the top layer is most energetically favorable. Compared to the undoped surface, those Sn and O atoms located above Ti atom tend to move toward the bulk side. Besides the surface relaxations, the doping of Ti has significant influences on the electronic structures of Sn O2 (110) surface, including the value and position of minimum band gap, the components of valence and conduction bands, the distributions of the charge densities, and the work function of the surface. Furthermore, the effects introduced by the substitution of Ti atom observed in the experiments can be well explained when the sixfold-coordinated Sn atom at the first layer is replaced by Ti atom.
| Original language | English (US) |
|---|---|
| Article number | 054704 |
| Journal | Journal of Chemical Physics |
| Volume | 124 |
| Issue number | 5 |
| DOIs | |
| State | Published - 2006 |
| Externally published | Yes |
Bibliographical note
Funding Information:This work is supported by grants from the Natural Science Foundation of China (Grant Nos. 20273013 and 20303002) and the State Key Laboratory of Structural Chemistry. We are also grateful for the funds from the Fujian Provincial Government and Fuzhou University (2004-XY-04). Table I. Calculated structural parameters and the doping energies ( E doping ) of Ti-doped Sn O 2 ( 110 ) surface. Undoped Ti 5 f -doped Ti 6 f -doped Ti 5 i -doped Ti 6 i -doped surface model model model model Displacement (Å) along the [110] direction with respect to the ideal surface Me 5 f a − 0.078 b − 0.069 ( − 0.184 ) c − 0.083 − 0.144 − 0.121 Me 6 f 0.246 0.246 0.116(0.316) 0.234 0.188 Me 5 i − 0.032 − 0.026 − 0.035 − 0.034 ( − 0.087 ) − 0.059 Me 6 i 0.116 0.121 0.122 0.096 0.074(0.125) O2 0.102 0.114 − 0.030 0.085 0.049 O3 0.166 0.164 0.167 0.175 0.167 O5 − 0.016 − 0.015 − 0.016 0.078 − 0.038 O6 0.113 0.112 0.104 0.088 0.065 Bond length (Å) O2- Me 6 f 2.004 2.006 2.065(1.829) 2.006 2.009 O3- Me 6 f 2.148 2.195 2.147(2.117) 2.143 2.143 O3- Me 5 f 2.072 2.093 (1.982) 2.089 2.073 2.072 O5- Me 5 f 2.013 2.023 (1.851) 2.009 2.011 2.007 O5- Me 5 i 2.103 2.120 2.107 2.112(2.054) 2.099 O6- Me 6 f 2.187 2.189 2.129(2.210) 2.183 2.218 O6- Me 6 i 2.073 2.061 2.059 2.068 2.068(1.952) Work function 7.48 7.54 7.25 7.50 7.32 (eV) E doping ( eV ) ⋯ − 5.5776 − 5.9412 − 5.5825 − 5.4296 a The symbol of Me denotes metal atom, namely, Sn or Ti atom. b The negative and positive values indicate that the atom moves toward the bulk and vacuum sides, respectively. c The values shown in parentheses are corresponding to the results for Ti atom. FIG. 1. (a) Bulk structure of Sn O 2 . (b) Schematic top view of Sn O 2 ( 110 ) surface and the rectangle area indicates the ( 2 × 1 ) supercell employed in the work. (c) Schematic side view of the Sn O 2 ( 110 ) surface. Only three layers are presented in the figure and the symbol of Me denotes metal atoms, namely, Sn or Ti. The large and small spheres indicate the oxygen and metal atoms, respectively. FIG. 2. Band structures of the undoped and Ti-doped Sn O 2 ( 110 ) surface. In the figures, the energy bands primarily originated from the Sn 5 f 5 s , O2 2 p x , O2 2 p y , O2 2 p z , and Ti 3 d orbitals are labeled by filled circle, filled rectangle, cross, hollow rectangle, and hollow circle, respectively. All the energies shown are reported with respect to the Fermi level. FIG. 3. (a) Total DOS and (b) partial DOS of O2 atom for the undoped and Ti-doped Sn O 2 ( 110 ) surface. All the energies shown are reported with respect to the Fermi level. FIG. 4. Total (left) and difference (right) charge-density maps at the (1 1 ¯ 0) plane for (a) Ti 5 f -doped and (b) Ti 6 f -doped Sn O 2 ( 110 ) surfaces. For each doping model, the (1 1 ¯ 0) planes through Me 5 f and Me 6 f atoms are considered, respectively. In the difference charge-density maps, the solid and dashed lines indicate the increasing and decreasing charge densities, respectively. FIG. 5. Distributions of charge density associated with the surface states for Ti 6 f -doped Sn O 2 ( 110 ) surface. The dashed lines in (a) indicate a ( 2 × 1 ) supercell and as shown in (b), the x and y axes are along the [001] and [ 1 ¯ 10] directions, respectively.