The formation of nano-dot and nano-ring structures in colloidal monolayer lithography

Monolayers of colloidal particles formed in a self-organizing process upon drying of a colloidal suspension are used as lithographic masks. After deposition of a thin metal layer, the mask is detached from the surface. The resulting surface is examined with optical, scanning electron, and atomic force microscopes. In addition to the well-known triangular structures, which reflect the gaps in the hexagonal arrangement of the particles, we observed the following additional features: hillocks (nano-dots) found just below and nano-rings found around the original location of the particles. These features may develop during detachment (hillocks) and formation (rings) of the mask, respectively. Hillocks develop as a consequence of the adhesion of the particles on the surface, whereas rings are formed from organic residuals in the suspension. We show that these features can be used to fabricate fluorescent dye rings of submicron size.