Sejong Kim

Patterned forest-assembly of single-wall carbon nanotubes on gold using a non-thiol functionalization technique

An approach for non-thiol functionalization of single-wall carbon nanotubes (SWNTs) on gold was demonstrated via an Fe3+-assisted self-assembly technique. Upon immersion of gold into a pH 2.2 aqueous FeCl3 solution, FeCl3 oxidized the gold surface, due to the aqua regia effect, resulting in the formation of films of FeO(OH)–FeOCl crystallites. Subsequent immersion into a SWNT dimethylformamide (DMF) dispersion led to needle-like forest assemblies of SWNTs based on metal-assisted chelation and electrostatic interactions. Two approaches for surface patterning of these SWNT forests were investigated based on shadow-mask evaporation and conventional photolithographic lift-off to localize FeO(OH)–FeOCl/Au composite pads on Si substrates. The strong adhesion of Fe3+ ions onto silica surfaces can be partially overcome by repeated washes in aqueous HCl solution (pH < 4), and completely overcome by photoresist-assisted protection which prevents unwanted Fe3+ ions from complexing with the unexposed silica surfaces. Such patterned Fe3+-functionalized Au structures provided the basis for the site-specific forest-assembly of SWNTs as characterized by atomic force microscopy (AFM) and resonance Raman spectroscopy.

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 10μm monodispersed polystyrene microspheres, allowing a grain-boundary-free single-crystal monolayer domain of ca. 200μm 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.

Dielectrophoretic Force-Induced Assembly Technique for the Fabrication of 2D Colloidal Photonic Crystals

Dielectrophoretic force-induced assembly technique was used to achieve close-packed 2D colloidal photonic crystals on parallel plate gold electrodes. These gold electrodes were patterned using conventional UV photolithography technique. The width and length of the parallel plates were 280 μm and 3 mm, respectively. The experimental tests conducted with 5.3 μm carboxyl functionalized polystyrene (PS) particles at various AC voltages, frequencies and particle concentrations showed that colloidal photonic crystals were fabricated on the ground electrode, instead of the working electrode, which may be attributed to the electro-osmotic flow and dipole-dipole attractions between the colloidal particles. It is concluded that this study provides promising results for the 2D colloidal photonic fabrication for the photonic industry.Copyright

Fabrication and Immobilization of 2D Colloidal Photonic Crystals

A dielectrophoretic, DEP, force induced assembly technique was used to achieve close-packed 2D colloidal photonic crystals on a substrate. The experimental tests were conducted on 5.3 μm carboxyl fictionalized polystyrene (PS) particles at a 6 AC Voltage and 1 MHz frequency. After the crystal was completely formed at the center of electrodes, a polyacrylamide solution was added to the system to immobilize the photonic crystals.Copyright

Micro-Machining of DNA Linked 2D Colloidal Photonic Crystals Using a Nd:YAG Laser

DNA linked 2D colloidal photonic crystals were micromachined using a pulsed laser to creat controlled line defect and hexagonal shapes. 2D photonic crystals were initially self-assembled via 1.8 µm polystyrene microspheres on functionalized glass substrates.