Fabrication of crack-free colloidal crystals using a modified vertical deposition method

We report on a novel template-free method for the fabrication of crack-free colloidal crystals by using a modified vertical deposition method. In this method, a colloidal suspension of silica spheres containing a silica precursor (an acidic tetraethyl orthosilicate (TEOS) solution) was used in the vertical deposition fabrication process. Hydrolysis of the silica precursor produced silica species, which filled up the voids between the self-assembled silica spheres to avoid the formation of cracks upon drying of the colloidal crystal film. The silica in the interstices of the silica beads can be easily removed using hydrofluoric acid vapor, leaving behind a crack-free colloidal crystal film. The amount of the silica precursor solution needed to fabricate crack-free film increased with the increasing number of layers of silica spheres. When an excessive amount of the silica precursor solution was added in the vertical deposition process of producing silica sphere bilayer, the resultant colloidal crystal film curled and peeled off from the substrate and a large-area nanobowl array was left on the substrate.