  The attachment of semiconducting nanoparticles to carbon nanotubes is one of
the most challenging subjects in nanotechnology. Successful high coverage
attachment and control over the charge transfer mechanism and photo-current
generation opens a wide field of new applications such as highly effective
solar cells and fibre-enhanced polymers. In this work we study the charge
transfer in individual double-wall carbon nanotubes highly covered with uniform
ZnO nanoparticles. The synthetic colloidal procedure was chosen to avoid
long-chained ligands at the nanoparticle-nanotube interface. The resulting
composite material was used as conductive channel in a field effect transistor
device and the electrical photo-response was analysed under various conditions.
By means of the transfer characteristics we could elucidate the mechanism of
charge transfer from non-covalently attached semiconducting nanoparticles to
carbon nanotubes. The role of positive charges remaining on the nanoparticles
is discussed in terms of a gating effect.
