Fabrication of a two-dimensional periodic non-close-packed array of polystyrene particles

We report a simple technique for the fabrication of a two-dimensional periodic non-close- packed array of nonspherical particles. The technique exploits the self-assembly of uniformly sized colloidal microspheres on the surface of a Si substrate followed by reactive ion etching (RIE) that converts the spheres into nonspherical particles. Single and double layers of packed colloidal polystyrene microspheres of uniform size (diameter 1.2 mum) were spin-coated onto cleaned Si substrates. The samples were then exposed to reactive ions in an RIE unit operating under a mixture of CF4 and O-2 gases. Due to preferential etching in the direction normal to the surface of the substrate, the rnicrospheres were reduced to a nonspherical form resembling a biconvex microlens. Moreover, the periodic nature of the previously packed layer was preserved during the etching process. As a result, we obtained two-dimensional periodic non-close-packed arrays of nonspherical particles. In this work, we report the systematic dependence of the dimensions of the polystyrene particles on the duration of the exposure to RIE. In addition, the resultant patterned Si substrates were further utilized as templates for directed assembly of unique arrangernents of microspheres with different diameters.