Single phase ZnO submicrotubes as a replica of electrospun polymer fiber template by atomic layer deposition

• ZnO tubes were replicated from the electrospun fibers by atomic layer deposition.
• ZnO tubes exhibited unique optical properties from their quantum-confinement.
• Band gap energies for ZnO films are much lower than for single crystalline ZnO.
• Ultraviolet light is completely absorbed by ZnO tubes.
• Such self-supported ZnO tubes can be reclaimed for use in future applications.

Free-standing and highly interconnected ZnO tubes consisting of nanostructured single phase grains are fabricated by atomic layer deposition (ALD) combined with the electrospinning technique. Hereby, electrospun poly(vinyl pyrrolidone) fiber mat is used as a soft template for coating with zinc oxide. The deposition is conducted onto the template at 70 °C by using diethylzinc and water as ALD precursors. The crystal structure, microstructure and optical properties of the ZnO deposited layers are studied in detail by transmission electron microscopy and X-ray diffraction before and after calcination. After calcination in air at 500 °C for 4 h the morphology of the wedge-like grains transforms into platelet-like structures with lattice parameters similar to those of the standard bulk polycrystalline ZnO. The resulting nanostructured ZnO tubes exhibit unique optical properties, which arose from the quantum-confinement of ZnO thin films prepared by ALD. The measured band gap energies for both the as-deposited and the calcined ZnO films are much lower than that of bulk ZnO or the single crystalline ZnO. Furthermore, the ultraviolet light is completely absorbed in both cases. The self-supported free-standing polycrystalline ZnO tubes can be easily handled and are bearing high potential for future applications related to catalysis, electronics, photonics, sensing, medicine and controlled drug release.