Dielectrophoretic assembly of grain-boundary-free 2D colloidal single crystals

Dielectrophoresis (DEP) force-assisted assembly of a colloidal single photonic-crystal monolayer in a microfluidic chamber was demonstrated. Negative DEP force with a high-frequency AC electric field induced the compression of colloidal microspheres to form a colloidal crystal domain at the center of a hexapolar-shaped electrode. While typical assembly by monotonic DEP force forms multicrystalline domains containing crystal defects, repetitions of the DEP/relaxation cycle significantly facilitated crystal growth of 10 μm monodispersed polystyrene microspheres, allowing a grain-boundary-free single-crystal monolayer domain of ca. 200 μm in size. Microsphere size as well as size distribution affected the formation of the single-crystal domain. A simple method was used to immobilize the single-crystal domain on the glass substrate without losing its crystallinity.

The present study deals with a dielectrophoresis (DEP) force-assisted assembly of 2D colloidal photonic crystal (PC) fabrication in a microfluidic device. In this process, negative DEP force with high-frequency electric field was used to form a colloidal crystal domain at the center of an hexapolar shape electrode without any boundary. A simple method was utilized to immobilize the single-crystal domain on the glass substrate without losing its crystallinity. This study may open up new possibilities to fabricate the simple, rapid, and high efficient colloidal PCs for various applications. Colloidal crystal growth process of 10 μm microsphere (left) and its crystallinity profile (right) by DEP compression/relaxation cycles.Figure optionsDownload high-quality image (74 K)Download as PowerPoint slideResearch highlights
► The grain-boundary-free 2D colloidal single crystalline monolayer domains with colloidal microspheres were fabricated using dielectrophoretic forces associated with hexapolar electrodes in a microfluidics.
► By appropriate manipulation of DEP/relaxation cycle, crystal growth of colloidal microspheres was facilitated to follow formation of a grain-boundary-free, single crystalline, monolayer domain of ca. 200 μm in size.
► This result may open up new possibilities on colloidal photonic crystals and their manipulation in the near future.