Student Project Abstracts 2005 - Pluto - University of Washington

Barium Titanate Doped Sol-Gel for Electro-Optic DevicesDeniz CivayUniversity of WashingtonNasser Peyghambarian, Robert Norwood,and Chris DeRosePeyghambarian Lab, Optical Science CenterThe University of ArizonaThe goal of my research was to successfully dope BaTiO 3nanocrystals into a sol-gel matrix,creating an electro-optic (EO) composite. After poling I determined the EO propertiesof the composite material. The resulting material exhibits an EO coefficient of 4pm/Vhowever poling conditions are not yet optimized. The advantage of using sol-gel is that thecomposite material will be photopatternable.RESEARCH METHODSI began my research by reviewing relevant literature. Thenanocrystals that have had some success in this field are PbTiO 3and BaTiO 3. However PbTiO 3and BaTiO 3nanocrystals have notyet been doped into sol-gel. BaTiO 3has a high EO coefficient butits high dielectric constant limits high speed and wide bandwidthoperation. The low dielectric constant of sol-gel served to lowerthe overall dielectric constant of the composite improving thebandwidth of the material. I purchased some BaTiO 3nanocrystalsfrom Sigma-Aldrich and TPL, inc. in order to perform theexperiments. The kind of testing that I performed on the BaTiO 3nanocrystal composite films was to determine the EO coefficientand loss.INTRODUCTION TO THEORYI am investigating electro-optic nanocomposites because solgelis photopatternable. Doping sol-gel with an EO nanocrystalresults in a photopatternable EO material. Barium titanatenanocrystals are being used because of the high EO coefficient of150pm/V. Barium titanate nanocrystals are also easily accessibleand cheap.Some important material properties to consider are the scatteringloss, dielectric constant and electro-optic coefficient. Thescattering loss is a measure of how much energy is lost from abeam of light passing through a material due to inhomogeneities.See Figure 1 below for an illustration of this phenomenon.Another important material property is the dielectric constant.The dielectric constant limits operational bandwidth. Ideallythe dielectric constant for optical and electrical waves shouldbe matched. The third important material property to consideris the electro-optic coefficient. The electro-optic coefficient isa measure of how much the index of refraction changes with anapplied electric field.Before starting the experimental procedure I used the Maxwell-GarnetTheory to model the scatting loss and composite dielectricconstant. The key variables in the Maxwell-Garnet Theoryare the nanocrystal radius, the wavelength of the incominglight, the dielectric constant of the nanocrystal and sol-gel, therefractive index of the nanocrystal and sol-gel, and the volumefraction.CALCULATIONSThe following equations are based on the Maxwell-GarnetTheory.Equation 1:C sca= (8/3)*[(2*π*n c*r)/( λ)] 4 *{[( n c/ n m) 2 -1]/[( n c/ n m) 2 +2]} 2 *π*r 2Where:n m= index of refraction of the sol-gel = 1.5n p= index of refraction of the particle = 2.3r = average particle radius = 20nmλ = wavelength of light = 1550nmC sca= .389657701Figure 1. An illustration of scattering loss.Equation 2:α sca= (3*η*C sca)/(4*π*r 3 )CMDITR Review of Undergraduate Research Vol. 2 No. 1 Summer 2005 13