of substrates with virtually any material composition or
shape. For example, SiNW- and SWNT-BBFs were transferred
directly to thin plastic sheets, a half-cylinder, a watch glass, and
suspended across open frames as free-standing films (Fig. 7a–d),
thus demonstrating much greater flexibility of this approach
over other assembly approaches reported previously.
Our BBF approach also has the potential to be scaled to very
large area structures, in analogy to large plastic films manufactured
in industry.24–26 As an initial demonstration of this point,
we have successfully transferred SWNT-BBFs to 200 mm wafers
(Fig. 7e), where the embedded SWNTs are uniformly aligned
across the wafer surface, and transferred a SiNW-BBF to a rectangular
9 inch 12 inch flexible plastic sheet (Fig. 7f) with good
control of SiNW alignment and density across the entire flexible
sheet. Both of these examples are the largest demonstrations to
date for aligned NWs and NTs.
2.6 Application of BBFs: SiNW FET arrays
To demonstrate the potentially broad application of these
nanomaterial-BBFs in electronics, large arrays of independently
addressable NW FETs were fabricated using SiNW-BBFs transferred
to 3 inch diameter flexible plastic substrates. This straightforward
transfer of aligned SiNW-BBFs to large substrates
makes this process considerably more efficient than previously
reported fluid-directed16 and Langmuir–Blodgett6 assembly
methods.