Surface phonons of the Si(111): In-(4x1) and (8x2) phases

The reversible phase transition of the Si(111):In-(4x1) surface has been studied using Raman spectroscopy and the symmetry, frequencies, and linewidths of the surface phonon modes have been determined. Dramatically different behavior has been identified for vibrational motion in the direction of the In chains and orthogonal to them. The differences in the Raman spectra of the room and low temperature surface are discussed in terms of the Peierls transition model and a recent dynamical soft shear distortion model. The measurements are found to be consistent with the former model, while some difficulties arise for the latter model. A combined Peierls transition and soft shear distortion model is consistent with the data, but is lacking detail. The Raman spectra presented here represent a challenge in developing theoretical models of this complex system

Characterization of domain distributions by second harmonic generation in ferroelectrics

Domain orientations and their volume ratios in ferroelectrics are recognized as a compelling topic recently for domain switching dynamics and domain stability in devices application. Here, an optimized second harmonic generation method has been explored for ferroelectric domain characterization. Combing a unique theoretical model with azimuth-polarization-dependent second harmonic generation response, the complex domain components and their distributions can be rigidly determined in ferroelectric thin films. Using the proposed model, the domain structures of rhombohedral BiFeO3 films with 71° and 109° domain wall, and, tetragonal BiFeO3, Pb(Zr0.2Ti0.8)O3, and BaTiO3 ferroelectric thin films are analyzed and the corresponding polarization variants are determined. This work could provide a powerful and all-optical method to track and evaluate the evolution of ferroelectric domains in the ferroelectric-based devices

Solid-Liquid Crystal Interfaces Probed by Optical Second-Harmonic Generation

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