Density Functional Theory Simulations of Structures and Properties for Ag-Doped ZnO Nanotubes

Incorporating silver in ZnO has attracted a lot of interest in recent years to fabricate p-type ZnO, as the naturally occurring ZnO is n-type material due to its native defects such as zinc interstitials and oxygen vacancies. In this work, the structural, electronic, and optical properties of pure and Ag-doped (8, 0) ZnO SWNTs were investigated by using density functional theory (DFT). The optimized structures present buckling side wall surfaces. The configurations with Ag atoms replacing Zn atoms are p-type semiconduction materials while the configuration with Ag atom added out of the surface of ZnO SWNTs is n-type semiconduction material. The optical properties based on dielectric function and absorption coefficient were discussed. It was found that the Ag-doped (8, 0) ZnO SWNTs have absorption in the visible-light region, and the absorption intensity is enhanced with the increase of Ag concentration. Our results indicate that the Ag-doped ZnO nanotubes could have a better performance as a photocatalyst. The calculations of Ag-doped ZnO slabs terminated with (10-10) surfaces are also presented to simulate the crystalline nanotubes synthesized in experiments, and the results are compared with that of ZnO SWNTs.