Qualitative Models for the Photoresponse and Capacitance of Annealed Titania Nanotubes
F. Di Quarto.
Physicochemical characterization of annealed TiO2 nanotubes (TNTs) was conducted by using
photocurrent spectroscopy and differential capacitance techniques. It has been shown that the geometry
and architecture of nanotubes determine how photogenerated electrons and holes are separated
and transferred. Photocurrent generation in TNTs is a consequence of two phenomena; drifting of
holes into the electrolyte and diffusion of electrons toward the substrate. These two processes have
been shown to be independent of the anodic polarization. The capacitance of TiO2 nanotubes is also affected by their
geometry. In anodic potentials, with respect to the flat band potential of the underlying barrier layer, the capacitance is
mainly controlled by the barrier layer because nanotubes are almost inactive. In the cathodic potential region, electrons injected
from the substrate into the conduction band of TiO2 induce nanotubes to behave more like porous metallic
electrodes. As a consequence, the electrochemical double layer along TNTs large surface area causes high values of capacitance.
Keywords: Annealing, anodization, capacitance, nanotubes, photocurrent spectroscopy, photoresponse, TiO2.
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