Nanometer positioning, parallel alignment, and placement of single anisotropic nanoparticles using hydrodynamic forces in cylindrical droplets

Droplets of liquid drying on a surface with pinned contact area develop an internal hydrodynamic flow that carries entrained particles to the air-liquid-substrate interface. We use this phenomenon in cylindrical, micrometer-sized droplets of large aspect ratio (more than 1000:1) to align, position, and place individual anisotropic nanostructures such as single-walled carbon nanotubes (SWNT). More than 84% of SWNT are aligned in parallel within 50 relative to the target axis of alignment. A potential flow model accurately describes and quantifies the statistical variation in the positioning of the nanostructures. We demonstrate for the first time the top-down parallel alignment and placement of individual (unbundled) nanotubes from solution electrically contacted across gold electrodes.