  Poly(ethylene imine) functionalized carbon nanotube thin films, prepared
using the vacuum filtration method, were decorated with Au nanoparticles by in
situ reduction of HAuCl4 under mild conditions. These Au nanoparticles were
subsequently employed for the growth of GaAs nanowires (NWs) by the
vapor-liquid-solid process in a gas source molecular beam epitaxy system. The
process resulted in the dense growth of GaAs NWs across the entire surface of
the single-walled nanotube (SWNT) films. The NWs, which were orientated in a
variety of angles with respect to the SWNT films, ranged in diameter between 20
to 200 nm, with heights up to 2.5 um. Transmission electron microscopy analysis
of the NW-SWNT interface indicated that NW growth was initiated upon the
surface of the nanotube composite films. Photoluminescence characterization of
a single NW specimen showed high optical quality. Rectifying asymmetric
current-voltage behavior was observed from contacted NW ensembles and
attributed to the core-shell pn-junction within the NWs. Potential applications
of such novel hybrid architectures include flexible solar cells, displays, and
sensors.
