Nano-scaled structures through charged particle interactions

The challenge of additive nanomanufacturing is to create and assemble literally quadrillions of nano-scaled structures. That cannot be done with typical 1-nozzle / 1-trace techniques. Instead there must be a utilization of macro-scale (e.g. easily controlled) forces to assemble large numbers of structures in parallel. For example, physical and chemical vapor deposition use momentum, condensation, and chemical reactions to deposit coatings, grow nanotubes, and form nanostructures from gas-phase precursors in a vacuum. An intriguing challenge is to utilize similar techniques, but move from traditional gas-phase materials in a vacuum to nanoparticles at atmospheric conditions. That transition would enable 1) larger area coating and cheaper processes, 2) an important meso-scale of structures that are on the order of 100's of nanometers to micrometers, which is the scale for wetting, adhesion, and other surface interactions, and 3) a straightforward path to polymer-particle nanocomposite structures by depositing multiple materials either in parallel or in sequence. We are investigating additive nanomanufacturing using nanoparticles formed by electrospray ionization (ESI). One key challenge is to determine the interplay between particle charge/momentum and the electric fields at the substrate to control assembly. Relevant forces include attraction to the grounded substrate, repulsion from likecharged particles in the spray, and repulsion from previously deposited particles or electrode patterning on the substrate. We examine three different cases: an electrically nonconductive substrate (Parylene), a nonconductive substrate with 1 mm gold bands about 1mm apart, and a nonconductive substrate with 1 mm gold bands 3 mm apart. These three cases give vital insight into the length-scales at which structures begin to develop in large-scale nanoparticle deposition systems. We show that the nature of the substrate did not appear to significantly affect the bulk spray, but deposition was strongly focused onto conductive, grounded bands. We also showed a gradient in the deposition with a length scale on the order of 1-100 μm.