Small diameter TiO2 nanotubes with enhanced photoresponsivity

We report ultraviolet (UV) light detection of thin wall TiO2 nanotubes (TNTs) with open diameter similar to 20 nm obtained by a two anodization procedure. This small diameter nanotubular geometry shows significant enhancement of the photoresponsivity and results in a large increase of photocurrent. The photocurrent is one order higher than that of classical nanotubes with diameter of 140 nm at -1.0 V bias. We attribute this improvement to the modulation of hole carrier density as a result of field effects from the diameter-dependent population of the surface-trapped electrons. This finding demonstrates inherent size effects of internal gain in semiconductor nanotubes. (C) 2012 Elsevier B.V. All rights reserved.