MRSEC Events

Wednesday, November 15, 2006, 1:00 PM-2:00 PM
IBM ALmaden Research Center, Room H2-214

Ryan J. Kershner, Ph.D.
CPIMA Postdoctoral Scholar
Stanford University

ABSTRACT

Colloidal systems have gained much attention in recent years for their numerous applications in microfluidics, photonics, drug-delivery, and other rapidly advancing fields. The key to the success of small particles in these areas remains their satisfactory assembly into functional devices. This talk presents two parallel approaches for the assembly of a model system of silica particles, with an eye towards both the fundamental physics and the fabrication of a device exhibiting interesting optical properties. In the first example, an electric field assisted assembly process is studied in detail. A system of platinum microelectrodes was fabricated on a sapphire substrate and used to manipulate 1.58 µm silica particles in-plane. A digital video system allowed direct observation of the motion of particles far from the electrodes and their deposition onto the working electrode during application of a DC potential. The role of Faradaic processes and the diffusion of potential determining ions in electrophoretic deposition are investigated. The second part of the talk presents recent success in the fabrication of large-domain colloidal crystals for photonics applications. In this case, sub-micron particles were self-assembled onto patterned substrates, facilitating templated epitaxial growth of millimeter scale single domain crystals with controlled crystallographic orientation. Laser scanning confocal microscopy was used to characterize the resulting templated structures. Spectroscopy data illustrating the interesting photonic properties of the crystals will also be presented. More recent work demonstrates the controlled placement of individual defect states within an ordered photonic crystal host using laser tweezers. Arrays of optical traps were utilized to grab individual ZnS core/silica shell nanoparticles (< 150 nm) and guide them through the pore structure of a synthetic opal to pre-determined locations. Simple structures consisting of 3-6 particles were successfully fabricated as a proof of concept, showing promise for the fabrication of next generation three dimensional photonic waveguides. Particle arrangements were fixed in place through polymerization of a photosensitive hydrogel, with the wavelength tuned far from that of the laser trap. Results obtained using Au nanoparticles also demonstrates the flexibility of this technique for controlling composition.