  Controlled and uniform assembly of "bottom-up" nanowire (NW) materials with
high scalability has been one of the significant bottleneck challenges facing
the potential integration of nanowires for both nano and macro electronic
circuit applications. Many efforts have focused on tackling this challenge, and
while significant progress has been made, still most presented approaches lack
either the desired controllability in the positioning of nanowires or the
needed uniformity over large scales. Here, we demonstrate wafer-scale assembly
of highly ordered, dense, and regular arrays of NWs with high uniformity and
reproducibility through a simple contact printing process. We demonstrate
contact printing as a versatile strategy for direct transfer and controlled
positioning of various NW materials into complex structural configurations on
substrates. The assembled NW pitch is shown to be readily modulated through the
surface chemical treatment of the receiver substrate, with the highest density
approaching ~8 NW/um, ~95% directional alignment and wafer-scale uniformity.
Furthermore, we demonstrate that our printing approach enables large-scale
integration of NW arrays for various device structures on both Si and plastic
substrates, with a controlled semiconductor channel width, and therefore ON
current, ranging from a single NW (~10 nm) and up to ~250 um, consisting of a
parallel array of over 1,250 NWs.
