Low-temperature
ozone-assisted atomic layer deposition (ALD) of
SiO2 with four silane derivatives (3-aminopropyl)triethoxysilane
(APTES), bis(diethylamino)silane (BDEAS), diphenylaminosilane (DPAS),
and triethylsilane on carbon nanotubes (CNTs) leads to the one step
formation of SiO2 nanotubes. In the process, CNTs act as
templates and are removed during the ongoing deposition. From transmission
electron microscopy images, the formation of a void between the CNTs
surface and the SiO2 coating was observed, indicating an
unexpected removal of carbon from the CNTs. This gap grows as the
number of ALD cycles is increased, eventually leading to SiO2 nanotubes almost free of carbon. ATR-IR and EELS spectra proved
the SiO2 formation. Depending on the CNTs templates used
in this process, different morphologies of one-dimensional SiO2 nanostructures are obtained, including simple nanotubes,
hollow wall nanotubes, tube-in-tube structures, and SiO2 nanowires. The application of this process on vertically aligned
CNTs (VACNTs) templates allows the formation of a perfect SiO2 replica of the VACNTs. From experiments with different oxygen
and silicon precursors, it is proposed that peroxides and oxygen-based
radicals, which can be formed from the reaction of surface Si–H
species with ozone, are the main reactive species leading to the unexpected
etching of carbon from the CNTs during silica ALD.