Aligned deposition of bottom-up grown nanowires by two-directional pressure-controlled contact printing.

Aligned large-scale deposition of nanowires grown in a bottom-up manner with high yield is a persisting challenge but required to assemble single-nanowire devices effectively. Contact printing is a powerful strategy in this regard but requires so far adequate adjustment of the tribological surface interactions between nanowires and target substrate, e.g. by microtechnological surface patterning, chemical modifications or lift-off strategies. To expand the technological possibilities, we explored two-directional pressure-controlled contact printing as an alternative approach to efficiently transfer nanowires with controlled density and alignment angle onto target substrates through vertical-force control. To better understand this technology and the mechanical behavior of nanowires during the contact printing process, the dynamic bending behavior of nanowires under varying printing conditions is modeled by using the finite element method. We show that the density and angular orientation of transferred nanowires can be controlled using this three-axis printing approach, which thus enables potentially a controlled nanowire device fabrication on a large scale.

Surface-controlled contact printing for nanowire device fabrication on a large scale.

Assembly strategies for functional nanowire devices that merge bottom-up and top-down technologies have been debated for over a decade. Although several breakthroughs have been reported, nanowire device fabrication techniques remain generally incompatible with large-scale and high-yield top-down microelectronics manufacturing. Strategies enabling the controlled transfer of nanowires from the growth substrate to pre-defined locations on a target surface would help to address this challenge. Based on the promising concept of mechanical nanowire transfer, we developed the technique of surface-controlled contact printing, which is based purely on dry friction between a nanowire and a target surface. Surface features, so-called catchers, alter the local frictional force or deposition probability and allow the positioning of single nanowires. Surface-controlled contact printing extends the current scope of nanowire alignment strategies with the intention to facilitate efficient nanowire device fabrication. This is demonstrated by the simultaneous assembly of 36 nanowire resistors within a chip area of greater than 2 cm(2) aided only by mask-assisted photolithography.