Self-assembly of 10-mu m-sized objects into ordered three-dimensional arrays

This paper describes the self-assembly of small objects-polyhedral metal pl ates with largest dimensions of 10 to 30 mum-into highly ordered, three-dim ensional arrays. The plates were fabricated using photolithography and elec trodeposition techniques, and the faces of the plates were functionalized t o be hydrophobic or hydrophilic using self-assembled monolayers (SAMs). Sel f-assembly occurs in water through capillary interactions between thin film s of a hydrophobic liquid (a liquid prepolymer adhesive) coated onto the hy drophobic faces of the plates; coalescence of the adhesive films reduces th e interfacial free energy of the system and drives self-assembly. By alteri ng the size and surface-patterning of the plates, the external morphologies of the aggregates were varied. Curing the adhesive furnished mechanically stable aggregates that were characterized by scanning electron microscopy ( SEM). For assemblies formed by plates partially composed of a sacrificial m aterial, a subsequent etching step furnished fully open, three-dimensional microstructures. This work validates the use of capillary interactions for three-dimensional mesoscale self-assembly in the 10-mum-size regime and ope ns new avenues for the fabrication of complex, three-dimensional microstruc tures.