The assembly of micron sized glass spheres on structured surfaces by dewetting

Previous work [E.J. Tull, P.N. Bartlett, K.R. Ryan, Controlled assembly of micrometer-sized spheres: theory and application, Langmuir 23 (14) (2007) 7859–7873] has shown that many conventional assembly techniques are ineffective for the organisation of glassy spheres ≥5 μm in diameter, into sparse patterns of interest for optoelectronic device applications. In the present work the assembly of 10 μm glass spheres on gold coated surfaces containing a distribution of pits was investigated in order to determine the conditions required to assemble glass spheres into the pits but leave the top surface free of adhering spheres when the surface dewets. The gold surfaces were patterned with self-assembled monolayers of thiols in order to control the wetting of the surface. When the surface is uniformly hydrophilic spheres are found to adhere everywhere. When the surface is uniformly hydrophobic no spheres remain or the surface or in the pits. Only when the pits were hydrophilic and the top surface hydrophobic was found possible to assemble spheres selectively into the pits.