  We report on the passivation of surface defects of ZnO nanorods by surface
layer deposition. ZnO nanorods and ZnS-ZnO hybrid nanostructures are grown on
FTO coated glass substrate by chemical bath deposition method. XRD spectrum of
ZnO nanorods shows the preferential growth along the c-axis. SEM analysis
confirms the nearly aligned growth of the ZnO nanorods with a hexagonal shape.
XPS measurements were performed to confirm the deposition of the surface layer
and surface stoichiometry. Room temperature photoluminescence of ZnO nanorods
showed two emission bands, viz. the band edge emission and the blue-green
emission, with the latter being associated with the defect states arising from
the surface of ZnO nanorods. The band edge emission is significantly increased
as compared to blue-green emission after ZnS surface layer deposition on ZnO
nanorods. The quenching of blue-green emission is explained in terms of reduced
surface defects after ZnS deposition. Density functional theory (DFT)
calculations are used to understand the mechanisms of defect passivation in
ZnS-ZnO nanostructures and we show that the S atoms prefer the O site as
compared with the Zn and interstitial sites
