Luminescence and Raman Based Real Time Imaging of Ferroelectric Domain Walls
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0966-T08-03
Luminescence and Raman Based Real Time Imaging of Ferroelectric Domain Walls Volkmar Dierolf, Pavel Capek, and Christian Sandmann Physics, Lehigh University, 16 Memorial Drive East, Bethlehem, PA, 18015
ABSTRACT We studied ferroelectric domain wall regions in lithium niobate using the photoluminescence of intentionally doped rare earth ions (such as Er3+) as well as Raman spectroscopy and present an overview of the current status of our ongoing investigations. We find that the Er emission is a sensitive tool to observe changes in local electric fields as well as reconfiguration of defect dipoles across the domain wall. The Raman spectra, on the other hand can be used to identify charges that accumulate asymmetrically across a domain wall. We further demonstrate that the imaging methods offer sufficient sensitivity to observe the changes associated with a domain in real time while it is moving.
INTRODUCTION Structuring of ferroelectric domains with submicron precision has attracted significant attention in particular for materials such as LiNbO3 and LiTaO3 due to their important role in integrated and nonlinear optics leading to devices such as frequency converter using periodically poled structures or electro-optical lenses and prisms. To all efforts to further push the limits of the currently available technology, basic understanding of domain growth and the local structure of ferroelectric domain walls and its dependence on intrinsic defects and dopants is a key element. To this date, several studies have been performed to define the spatial extent of the static domain wall region both theoretically [1] and with different experimental methods [2-6]. However, measurements of the dynamics of the domain wall region have been limited to highspeed imaging of the transmitted light [7] and changes occurring on a slow (min) time scale [8] None of these techniques give information about the interaction of domain walls and intrinsic defects. Such information is difficult to obtain due to the lack of appropriate probe signals that characterize the intrinsic defects. In order to overcome this obstacle, we use intentionally doped rare earth ions as probes for the changes occurring under domain inversion. Our previous studies have demonstrated that e.g. Er3+ ions are excellent probes for local electric fields and the interaction with intrinsic defects [6, 9-11]. In this paper, we will review this method and its application to the imaging of domain walls regions. We will also give example on how it can be used to real-time diagnostics of moving domain walls. We further applied Raman spectroscopy to the imaging of domain wall regions. We will show that the ratio of LO -phonon mode intensity can be used to determine asymmetric charge distribution across a domain wall as they occur during heating and cooling as well as during application of electric fields and under domain inversion.
EXPERIMENTAL TECHNIQUES The samples in our studies come from a variety of sources. Undoped and Er-doped (0.02mol%) congruent LiNbO3 a
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