New Core/Shell Ta 2 O 5 -PMMA Nanocomposites for Applications as Polymer Waveguides
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1056-HH10-09
New Core/Shell Ta2O5-PMMA Nanocomposites for Applications as Polymer Waveguides Dorothée Vinga Szabó, Rolf Ochs, Sabine Schlabach, Eberhard Ritzhaupt-Kleissl, and Thomas Hanemann Institute of Materials Research III, Forschungszentrum Karlsruhe, P.O. Box 3640, Karlsruhe, 76021, Germany ABSTRACT To realize ceramic/polymer nanocomposites for polymer waveguides, PMMA-coated Ta2O5 nanoparticles are synthesized as core/shell particles. Therefore a gas-phase process is used: the Karlsruhe Microwave Plasma Process. The organic coating is supposed to reduce the agglomeration of the ceramic cores and should facilitate the incorporation into the polymer resin. TEM investigations of the nanoparticles exhibit crystalline and amorphous Ta2O5 with sizes around 3 to 6 nm, confirmed by electron diffraction. Although the polymer coating is not visible in TEM imaging, electron energy loss spectroscopy (EELS) exhibits a significant C-edge, proofing the organic coating. The Ta2O5/PMMA nanoparticles are incorporated with different weight fractions up to a maximum of 1 wt% by a dissolver stirrer into PMMA resin. The optical properties (refractive index, transmission) are determined as a function of the nanoparticle content. Compared to the pure polymer, the refractive index of the modified composite, measured at 633 nm, is increased by 0.001 and 0.004 at 0.1 wt% and 0.7 wt%, respectively. A similar tendency is observed at 1550 nm. The transmission in the near infrared (NIR) is similar to that of PMMA up to a content of 0.3 wt%. At higher nanoparticle contents the transmission decreases. The reduction in transmission is due to the presence of agglomerates larger then 1/10 of the applied wavelength, confirmed by TEM. The concept of incorporating inorganic/organic hybrid nanoparticles with intrinsic high refractive index in polymer matrices is very promising. A suitable effect regarding the refractive index for application of ceramic nanoparticle/polymer nanocomposites as polymer waveguides could be observed even with low particle concentration. INTRODUCTION Micro optical devices with tuned refractivity are of great technological interest e.g. in the area of polymer waveguide devices. They can be realized using nanocomposites made by embedding inorganic nanoparticles in a polymer, e.g. PMMA [1]. One necessary request for the nanoparticles in question is that they feature an appropriate large refractive index. This is, as a rule of thumb, the case for e.g. Al2O3, TiO2, ZrO2, HfO2, or Ta2O5. The second request concerns particle or agglomerate sizes: they must be below 1/10 of the used wavelength to avoid the influence of Rayleigh scattering (λ/10 criterion). Therefore, there is a need for synthesis processes that are able to produce isolated nanoparticles or soft agglomerates which can be dissociated easily during incorporation into a polymer. So far transparent nanocomposite thin films of rutile, TiO2 and polyvinyl alcohols have successfully been produced by two-step wet-chemical methods [2]. Those thin films contain particles w
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