An experimental insight into the structural and electronic characteristics of strontium-doped titanium dioxide nanotube arrays

The possibility of in situ doping during electrochemical anodization of titania nanotube arrays is demonstrated and the mechanism and variations in structural and electronic characteristics of the nanotube arrays as after doping is systematically explored. In the presence of strontium as the dopant, bulk analysis shows strontium mainly incorporated into the lattice of TiO₂. Surface analysis, however, reveals phase segregation of SrO in the TiO₂ matrix at high Sr doping levels. The near edge X-ray absorption fi ne structure (NEXAFS) spectroscopy analysis reveals that Sr₂₊ doping only alters the Ti and O ions interaction in the TiO₂ lattice on the surface with no effect on their individual charge states. An in-depth understanding of the dopant incorporation mechanism and distribution into TiO₂ nanotube arrays is achieved using high resolution transmission electron microscopy (HRTEM) and the high angle annular dark-fi eld scanning transmission electron microscopy (HAADF-STEM) coupled with the electron energy loss spectroscopy (EELS) measurements on the surface and bulk of the nanotubes. Upon their use to photoelectrochemically split water, the Sr-doped TiO₂ nanotube fi lm shows incident photon conversion effi ciencies (IPCE) as high as 65%. The enhanced light activity in conjunction with the ordered one-dimensional morphology makes the fabricated fi lms promising candidates for water photoelectrolysis.