Fabrication of hollow TiO2 nanotubes through atomic layer deposition and MWCNT templates

Titanium oxide (TiO2) nanotubes were synthetized by atomic layer deposition (ALD) coating multiwalled carbon nanotubes (MWCNTs) template. Thick wall (20 nm) TiO2 tubes were fabricated by coating directly the bare MWCNTs surface with TiO2 ALD. For thinner wall tubes (10 nm), very thin Al2O3 buffer layer was inserted to enhance the structural stability of the TiO2 tubes. Coatings were carried out at 100 degrees C in a hot-walls pulsed-bed ALD reactor. Trimethyl-aluminum (TMA) and Tetrakis(dimethylamino)titanium (TDMAT), where used as metal precursors and water as oxygen source. Wall thickness of TiO2 tubes was controlled by adjusting the number of ALD-cycles, as seen Transmission Electron Microscopy (TEM) images. Chemical characteristics of both Uncoated and coated MWCNTs were analyzed through a XPS and a FIR. Templates were removed by thermal oxidation, monitored by thermogravimetric analysis (TGA) up to 800 degrees C, finding thicker TiO2 layers shift up the degradation temperature of the templates. EDXS line scan in TEM confirined the coatings retained the concentric structure of the parent templates while attaining excellent wall thickness control. XRD, Raman spectroscopy and SAED confirm that TiO2 anatase is the only crystalline phase present after template removal. (C) 2016 Elsevier B.V. All rights reserved.