Polymer Nanocomposites

Major breakthroughs in photonics have often occurred when superb materials science is coupled with elegant and efficient device design/fabrication. Silica-based optical fiber, the semiconductor laser, the erbium doped fiber amplifier and the silica-on-silicon arrayed waveguide grating router are several notable examples of this phenomena. State-of-the-art photonics now requires the development of ever-higher degrees of integration, placing stringent demands on photonic materials technology, which ultimately must be suitable for the new field of nanophotonics. In parallel with these developments, the field of optical polymer nanocomposites (PNC) has emerged thanks to considerable advances in optical polymer materials, nanoparticle synthesis, nanoparticle functionalization and dispersion techniques. Optical PNCs have the potential to fulfill a broad range of photonic functions ranging from compact, narrowband filters, to electro-optical modulation at hundreds of GHz. To accomplish this, a clear understanding of optical polymer and nanoparticle properties is required, as well as an ability to effectively model and predict the properties of the PNC, and finally align these properties with the photonics engineering problem at hand.

We have recently explored a variety of PNC systems, each of which provides a distinct and instructive approach to the realization of designer optical materials with properties suitable for device applications. Melt processing, a conventional polymer process, has been found to provide unusually good nanoparticle dispersion, even for naked nanoparticles, by virtue of the large shear forces that develop during melt-processing. Highly loaded (30wt%) titania/polystyrene PNCs and other melt-processed PNCs were successfully infiltrated into silicon photonic crystal devices (as shown) as evidenced by the observed shift in the photonic band gap; Maxwell-Garnett theory effectively modeled the performance of this composites.

Processed PNCs were successfully infiltrated into silicon photonic crystal devices

In another example, an array of indium phosphide nanowires was embedded in polymethylmethacrylate and the electro-optic properties of the resulting composite indicated that the indium phosphide nanowires had exceptional electro-optic properties, with coefficients greater than 100pm/V.

Indium phosphide nanowires embedded in polymethylmethacrylate

This is an example where formation of the composite was critical to enabling the measurement of the electro-optic properties of the nanowires. In very recent work, we have developed a technique for nanoparticle photoactivated cationic polymerization, whereby the nanoparticle is the activation site for the growth of its own functionalization shell. This technique has recently been exploited to make magneto-optic PNCs, where functionalized magnetite nanoparticles are incorporated into acrylate copolymers. The resulting PNCs have exceptional magneto-optic properties and transparency, as evidenced by figures of merits approaching those of firmly established garnet materials. These examples demonstrate the breadth of photonic functionalities that can be realized in PNCs.

References

A. Lopez, Santiago, P. Gangopadhyay, J. Thomas, R. A. Norwood, A. Persoons, and N. Peyghambarian, “Faraday rotation in magnetite-polymethylmethacrylate core-shell nanocomposites with high optical quality,” Appl. Phys. Lett. 95, 143302 (2009).
C. J. Novotny, C. T. DeRose, R. A. Norwood, and P. K..L. Yu, “Linear electrooptic coefficient of InP nanowires,” Nanoletters 8, 1020 (2008).
S. Tay, J. Thomas, B. Momeni, M. Askari, A. Adibi, P. J. Hotchkiss, S. R. Marder, R. A. Norwood, and N. Peyghambarian, “Planar photonic crystals infiltrated with nanoparticle/polymer composites,” Appl. Phys. Lett. 91, 221109 (2007).