Fabrication and defect design in two-dimensional colloidal photonic crystals

Date of Completion

January 2003


Engineering, Materials Science




A two-dimensional photonic crystal structure was self-assembled via capillary forces from a colloidal polystyrene microparticle aqueous suspension with feature sizes ranging from 1.0 to 1.8 microns. Electrostatic and hybridized DNA bonding are utilized as mechanisms for adhering the particles to a glass substrate. To facilitate the formation of dense, close-packed, large area arrays a number of organizational affecting parameters will be examined such as: (i) contact angles between medium and substrate; (ii) mono-dispersity of the colloidal particle medium; and (iii) particle-substrate electrostatic interactions. Carefully controlled defects were scribed into the crystal structure by selectively removing a single particle or a small cluster of particles. The mechanism for removing said particles was thermal dissociation of the substrate-particle bonding and the near neighbor particle-particle bonds with a highly focused monochromatic Argon-Ion beam of 514nm light. The nature of the inter-particle and substrate bonding was probed by utilizing both electrostatic forces and DNA as binding agents in conjunction with varying the chemistry of the medium and surface chemistry of the particles and substrate such as: (i) number of base pairs of the DNA strand; (ii) global and intercalating dyes in the medium; (iii) NaCl concentration in the medium; (iv) the addition of a non-hybridizable spacer strand to the hybridizable DNA strand; (v) DNA annealing; and (vi) refractive index matching of medium to colloidal particles. Finally, the feasibility of utilizing an array of optical tweezers, generated by the interference of three carefully controlled Argon-Ion 514 nanometer beams, to self-assemble a colloidal particle array in aqueous solution was examined. ^