Local Optical Probes of Microwave Dielectric Dispersion in Ferroelectric Thin Films
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277 Mat. Res. Soc. Symp. Proc. Vol. 603 © 2000 Materials Research Society
In this paper, we report results from time-resolved confocal scanning optical microscopy (TRCSOM) experiments that measure the local soft-mode contribution to the dielectric response of ferroelectric thin films at microwave frequencies. Both the ferroelectric and paraelectric response are measured with diffraction-limited (-500 nm) spatial resolution and picosecond temporal resolution. The spatially inhomogeneous dielectric dispersion observed for the soft mode provides a direct experimental link between nanopolar structure and fast (sub-nanosecond)
dynamical response. EXPERIMENTAL DETAILS Bao.sSro.sTiO 3 thin films are grown on MgO substrates by off-axis co-sputtering from SrTiO 3 and BaTiO 3 targets5. The films are c-axis oriented and polycrystalline, with a high degree of in-plane order. The electrical properties of the films are also characterized at microwave frequencies 1-20 GHz. Silver/gold interdigitated electrodes are deposited on the sample, and s-parameter measurements are performed and analyzed using a series capacitor and resistor equivalent circuit model. The microwave measurements yield quality factors Q=el/c 2 50-70 for the samples investigated here5. Figure 1shows schematically the experimental arrangement for the TRCSOM measurements. Ultrashort (-120 fs) light pulses from a mode-locked Ti:Sapphire laser (repetition frequency o/2x -76 MHz) clock a phase-locked oscillator that produces a high
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