Sebastian K. Nett

Arrays of microlenses with variable focal lengths fabricated by restructuring polymer surfaces with an ink-jet device

We report of a method for fabricating two-dimensional, regular arrays of polymer microlenses with focal lengths variable between 0.2 and 4.5 mm. We first make concave microlenses by ink-jetting solvent on a polymer substrate with a commercial drop-on-demand device. Solvent evaporation restructures the surface by a series of combined effects, which are discussed. In the second step we obtain convex elastomeric microlenses by casting the template made in the first step. We demonstrate the good optical quality of the microlenses by characterising their surfaces with atomic force microscopy and white light interferometry, and by directly measuring their focal lengths with ad-hoc confocal laser scanning microscopy.

Template-free structuring of colloidal hetero-monolayers by inkjet printing and particle floating

Here we demonstrate the feasibility of a novel approach to simultaneously pattern surfaces with heterogeneous colloidal monolayers on various length scales from tens of µm down to nanometres by a combination of simple inkjet printing and nanosphere lithography. The process involves inkjet printing of different particle types in a pre-pattern with sparsely distributed particles on an initial substrate. After immersion in water the particles float off the substrate and self-assemble into a dense and hexagonally ordered colloidal monolayer, with a concomitant 1D contraction of the pre-pattern along the immersion direction. While nanosphere lithography yields the nanostructures, the superimposed µm scale pattern is defined by the inkjet printing process, leading to hexagonally ordered colloidal monolayers of various particles sizes or materials in parallel. Since the µm pattern with arbitrary shape is simply designed on a computer and printed, the process does not require any customized template or mask to be fabricated. Due to its simplicity the computer-assisted method shows great potential for automatization, which should substantially improve structure quality and turn it into a technologically promising approach.