Massively Scalable Self-Assembly of Nano and Microparticle Monolayers via Aerosol Assisted Deposition.

An extremely rapid process for self-assembling well-ordered, nano, and microparticle monolayers via a novel aerosolized method is presented. The novel technique can reach monolayer self-assembly rates as high as 268 cm2 min-1 from a single aerosolizing source and methods to reach faster monolayer self-assembly rates are outlined. A new physical mechanism describing the self-assembly process is presented and new insights enabling high-efficiency nanoparticle monolayer self-assembly are developed. In addition, well-ordered monolayer arrays from particles of various sizes, surface functionality, and materials are fabricated. This new technique enables a 93× increase in monolayer self-assembly rates compared to the current state of the art and has the potential to provide an extremely low-cost option for submicron nanomanufacturing.

Zeta Potential Dependent Self-Assembly for Very Large Area Nanosphere Lithography.

Nanosphere lithography offers a rapid, low-cost approach for patterning of large-area two-dimensional periodic nanostructures. However, a complete understanding of the nanosphere self-assembly process is necessary to enable further development and scaling of this technology. The self-assembly of nanospheres into two-dimensional periodic arrays has previously been attributed solely to the Marangoni force; however, we demonstrate that the ζ potential of the nanosphere solution is critically important for successful self-assembly to occur. We discuss and demonstrate how this insight can be used to greatly increase self-assembled 2D periodic array areas while decreasing patterning time and cost. As a representative application, we fabricate antireflection nanostructures on a transparent flexible polymer substrate suitable for use as a large-area (270 cm2), broadband, omnidirectional antireflection film.

Structural coloration with hourglass-shaped vertical silicon nanopillar arrays.

We demonstrate that arrays of hourglass-shaped nanopillars patterned into crystalline silicon substrates exhibit vibrant, highly controllable reflective structural coloration. Unlike structures with uniform sidewall profiles, the hourglass profile defines two separate regions on the pillar: a head and a body. The head acts as a suspended Mie resonator and is responsible for resonant reflectance, while the body acts to suppress broadband reflections from the surface. The combination of these effects gives rise to vibrant colors. The size of the nanopillars can be tuned to provide a variety of additive colors, including the RGB primaries. Experimental results are shown for nanopillar arrays fabricated using nanoimprint lithography and plasma etching. A finite difference time domain (FDTD) model is validated against these results and is used to elucidate the electromagnetic response of the nanopillars. Furthermore, a COMSOL model is used to investigate the angle dependence of the reflectance. In view of display applications, a genetic algorithm is used to optimize the nanopillar geometries for RGB color reflective pixels, showing that nearly all of the sRGB color space and most of the Adobe RGB color space can be covered with this technique.