Morphological, structural and optical characterization of SnO₂ nanotube arrays fabricated using anodic alumina (AAO) template-assisted atomic layer deposition

Self-aligned and equal-space SnO₂ nanotubes (NTs) with external diameters ranging from ca. 124 to ca. 325 nm and wall thickness of around 30 nm were synthesized by AAO template-assisted atomic layer deposition. The bulk and surface structure of the SnO₂ nanostructures were studied in detail by XRD and XPS techniques, respectively. The SnO₂ NTs were polycrystalline with an average crystallite size of ca. 3 nm. The structure analysis has revealed that the SnO₂ NTs are composed of the rutile-type SnO₂. The SnO₂ nanotube arrays with the smaller external diameters emitted green light centered at around 520 nm. The emission was ascribed to the radiative recombination between electrons trapped in shallow donor levels and holes at the intrinsic surface states, associated with the oxygen deficient sites near surface region. The PL intensity diminished with the nanotube diameter and spacing. With increasing external diameter of the SnO₂ nanotubes and decreasing the distance between the neighboring nanotubes, the emission become progressively weaker. The results demonstrate that the structure, morphology and arrangement of SnO₂ nanotubes play an important role in their luminescent properties.