Multiscale-architected Device Laboratory

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.

The development of ion-assisted aerosol lithography (IAAL) has enabled fabrication of complex threedimensional nanoparticle (NP) structures on conducting substrates. In this work, the applicability of the IAAL technique was investigated on non-conducting substrates. The NP structure growth process on a non-conducting substrate was found to self-terminate and the structures subsequently repel incoming charged NPs and scatter them away. Electric field calculations supported the experimental findings and confirmed that the electric field distortions owing to charge build-up within the structures prevented additional NP deposition thereon. To regulate the charge build-up without compromising the number of NPs available for assembly, a corona discharger and an ion trap were implemented. By varying the number of ions available in the assembly process, an optimum level of ion injection was found that allowed for a prolonged (>120 min) assembly of NP structures on non-conducting substrates without the unwanted scattering of NPs.