Large-Scale Assembly of Single Nanowires through Capillary-Assisted Dielectrophoresis

摘要

Semiconducting nanowires (NWs) are 3D nanoscale building blocks with promising applications in, for example, field-effect transistors (FETs), biosensors, and optoelectronic components. The fabrication of semiconducting NWs, synthesized by a bottom-up approach, has made impressive progress toward providing high-quality nanostructures made in tunable materials and heterostructures. However, postgrowth NW manipulation and positioning through a generic, large-scale alignment method remains a challenge in envisioning NW-based devices as credible commercial products. Different techniques, such as Langmuir-Blodgett deposition, dry transfer printing, and capillary force assembly, have been proposed. However, these methods cannot easily accomplish single-NW alignment and precise positioning without a certain degree of fabrication complexity, or the use of high-resolution patterning technique (electron-beam lithography) that is time-consuming and cost-ineffective, making the process difficult to adapt batch fabrication. Because of its potential to overcome these limitations, dielectrophoretic (DEP) assembly is receiving increasing attention. Smith et al. showed that a nonuniform electric field applied between interdigitated electrodes can induce significant polarization of dielectric nanostructures. The resulting DEP force allows the NWs moving in the solution to overcome other forces (e.g., hydrodynamic drag, gravity, electrothermal, intraparticle, and surface-particle adhesive forces) and to localize on the electrodes at specific predefined locations. More recent studies have advanced the DEP technique by improving both physical understanding and yield. However, some key issues remains to be managed in a simple way, in terms of: (ⅰ) improving the NW concentration in the DEP-attracting region, and (ⅱ) controlling the hydrodynamic forces exerted on the NWs while the solvent is dried.