Switching in the Presence of Defects Volkmar Dierolf, Lehigh University, DMR 1008075

1. Switching in the Presence of DefectsVolkmar Dierolf, Lehigh University, DMR 1008075 Outcome: Researchers at Lehigh University in collaboration with their US collaborators at Pennsylvania State University and their international partners in Germany (University of Bonn and Paderborn) have clarified the role of defects in the switching behavior of the commercially important lithium niobate material. Impact: In the quest for ever smaller dimensions of optical devices that use lithium niobatewith their ferroelectric axis pointing in different directions it is critical to control and exploit the influence of defects to maintain long-term stability. Explanation: In commercial available congruent lithium niobate material, the switching of the ferroelectric domain direction requires fields that depend on the history of the crystal. In particular, switching of a virgin crystals requires a significantly higher field compared to the field required to switch the direction back. This effect can be used to stabilize patterns of domains. The team of Prof. Dierolf has quantified the effect by determining the magnitude and direction of electric fields that are produced by intrinsic defects that do not reorient and are hence the origin of the effect. For this, they developed a technique based on Raman spectroscopy that lets them determine intrinsic electric fields down up Image of a ferroelectric domain wall visualize using the effect of defects as seen in Raman spectroscopy

2. Defect Induced Intrinsic Electric Fields Volkmar Dierolf, Lehigh University, DMR 1008075 Defects that are caused by the deficiency of Li in congruent lithium niobate and tantalate induces polar defects that strongly influence the ferroelectric switching behavior. The observed asymmetry of the ferroelectric hysteresis curves is attributed to internal fields created by these defects. Prof. Dierolf and his team has determined the size and directions of these fields utilizing in-situ Raman spectroscopy under applied electric fields and during domain inversion processes. Using the first for calibration, his team was able to determine the magnitude of the change in internal electric due to misaligned (“frustrated”) defects that occur after the inversion. The results supports theoretical prediction of the structure of the intrinsic defects developed early by the group. Spectral changes of line positions of al Raman mode during application of an external electric field and during domain inversion for congruent and stoichiometric LiNbO3

3. Underrepresented Groups in ResearchVolkmar Dierolf, Lehigh University, DMR 1008075 ”. The group of Prof. Dierolf at Lehigh University makes a sustained effort in offering research opportunities to students from under–represented groups such as female and African-Americans. In summer 2011, Zuri McClelland from UC Berkley spend 10 weeks in Prof. Dierolfs lab performing research on optical spectroscopy of materials. She studied the polarization depends of the emission and excitation of rare earth ions and related them to the lattice environments that these dopants are exposed to. She will present her results already in Sept. 2011 at the Joint Annual Conferences of the Associations for Black and Hispanic Physics. Zuri McClelland in the lab of Prof. Dierolf at Lehigh University Outcome: Coming to Lehigh Zuri was uncertain if she should pursuit graduate school in Physics but got convinced afterwards.