Controlled electrostatic focusing of charged aerosol nanoparticles via an electrified mask

We demonstrate controlled printing of charged nanoparticles using a metal coated stencil mask by applying an electric potential to engineer the electric field streamlines through the mask opening. The potential difference between the metal coated mask and the substrate generates an electrostatic lens effect which focuses the charged nanoparticles toward the center of the opening and hence reduces the size of the printed nanoparticle clusters. In contrast to previously reported ion induced focusing approach, the present method does not rely on ion accumulation, but simply requires changing the potential difference between the mask and the substrate to control the focusing of charged aerosols. By adjusting the potential difference between the mask and the substrate, electric field distortion near the mask opening can be precisely controlled. Using this approach, the printed patterns can be scaled down by up to a factor of 7.3 in each dimension from the mask opening, which enables printing of sub-micrometer sized particle clusters using a mask with micrometer scale opening sizes. Particle trajectories were calculated by solving the Langevin equation, and the resulting particle deposition profile was compared with the experimental results. Using this approach, a multi-material nanoparticle cluster array was fabricated by a sequential deposition of silver and copper nanoparticles after lateral translation of the mask, resulting in offset arrays of silver and copper nanoparticle clusters on the same substrate.