A mask for this pattern was produced by drop-casting a colloidal suspension of 2 µm polystyrene spheres on clean Si, producing a perfect hexagonally packed monolayer which is defect-free over millimeter dimensions. Fluoride ions were used to etch the triangular pattern in the voids between the microspheres. Removal of the masking spheres leaves the well-defined pattern of holes. Following subsequent microfabrication processes, these holes are filled with metals, producing a flat substrate with a large pattern of nano ?lightning rods? for optical field enhancement and spectroscopic applications. 10µm scan. Imaged with the MFP-3D AFM.
Image courtesy of S. MacLaren and M. Graca,
University of Illinois at Urbana-Champaign.