Monday, May 23, 2005Volume 5, Issue 3
David A. Scrymgeour
Advisor: Venkatraman Gopalan
Intercollegiate Materials
Local Structure and Shaping of Ferroelectric Domain Walls for Photonic Applications
Surprising asymmetry in the local electromechanical response across a single antiparallel ferroelectric domain wall is reported in lithium niobate. This material has established itself as a vital material in the field of nonlinear and electro-optics. Precisely patterning these ferroelectric domain structures on small length scales is a key to creating many optical devices, especially for laser frequency conversion. However, despite much study, fundamental understanding of the local structure of domain walls, which underpins device creation, is still elusive. Piezoelectric force microscopy (PFM) is used to investigate both the in-plane and out-of- plane electromechanical signals around 180° domain walls in congruent and near-stoichiometric lithium niobate. The observed asymmetry is shown to have a strong correlation to crystal stoichiometry, suggesting defect-domain wall interactions. The finite element method is used to simulate the electromechanical processes at the wall and reconstruct the imaging mechanisms. Agreement between the experiments and simulations is found in both form and magnitude. Together, these results suggest that while the structure of an ideal ferroelectric domain wall is understood to be atomically sharp (1 to 2 unit cells wide), small amounts of defects can change the local structure of a domain wall dramatically through defect-domain wall interactions.
