  Sensing response of individual single-crystal titania nanowires configured as
chemiresistors for detecting reducing (CO, H2) and oxidizing (O2) gases is
shown to be sensitive to visible light illumination. It is assumed that doping
of the TiO2 nanowires with C and/or N during carbon assisted vapor-solid growth
creates extrinsic states in the band gap close to the valence band maximum,
which enables photoactivity at the photon energies of visible light. The
inherently large surface-to-volume ratio of nanowires, along with facile
transport of the photo-generated carriers to/from the nanowires surface promote
the adsorption/desorption of donor/acceptor molecules, and therefore open the
possibility for visible light assisted gas sensing. The photo-catalytic
performance of TiO2 nanowire chemiresistors demonstrates the prospect of
combining light harvesting and sensing action in a single nanostructure.
