Vertical ZnO nanowire arrays may be beneficial to the
performance of certain devices, such as polymer-inorganic
solar cells,66 UV lasers,3 and vertical-field-effect transistors.67
Ordered arrays can be grown from a single-crystalline
substrate that has a small lattice mismatch and appropriate
symmetry (usually Al2O3 or GaN).3,68 Alternatively, a ZnO
thin film22,69 or a discontinuous layer of nanoscopic ZnO
seeds17 deposited on a nonepitaxial substrate (such as silicon
or glass) can act as a nucleation layer for wire growth. For
device applications, vertical growth from textured ZnO seeds
is appealing because the processing is low-cost, versatile,
and substrate-independent. Also, the nanowires can have
direct contact with the substrate without sitting atop a
disordered polycrystalline film