Organized one-dimensional nanostructures such as nanowires
and carbon nanotubes can possess unique physical properties
that make them potential key building blocks for the
manufacturing of next-generation high performance electronic,
optoelectronic and electromechanical systems.1–3 Yet, to realize
such applications and to further fundamental studies of these
materials will require development of effective methods for the
assembly of nanowires (NWs) and nanotubes (NTs) with
controlled location, orientation and spacing, hierarchically and
over large areas.
To this end, much effort has been placed on developing
methods of assembly of NWs and/or NTs.4–23 For example, the
Langmuir–Blodgett (LB) technique has been utilized to align
NWs with controlled spacing and recently similar results have
been achieved for single-walled nanotubes (SWNTs).5–8 In the
LB method, surfactant-wrapped NWs/SWNTs are slowly compressed
on an aqueous subphase to yield uniaxially-aligned
NWs/NTs. This technique produces parallel NWs/NTs with
controlled spacing down to close-contact, and can be used to
assemble more complex structures such as cross-bars by multiple
layer transfer steps. Functional devices based on such LB films
consisting of NWs or SWNTs have been fabricated,7,8 although
it is unclear whether the centimetre-square arrays of NWs can be
scaled further to larger areas with high efficiency and transferred
to non-rigid surfaces, such as flexible plastics.
Chemical modification of substrate surfaces has also been
widely used to assemble NWs and SWNTs.9–13 In this approach,
chemically-patterned substrates are dipped into a nanomaterialcontaining
solution during which NWs or SWNTs adsorb onto
the complementary patterned regions of the substrate. This
method shows promise for assembly of nanostructure arrays at
predetermined locations (determined by the chemical pattern),
orientation, and pattern shape or hierarchy, although larger
size patterns (e.g. on the order of several mm) of SWNTs exhibit