Probing Nanoscale Ferroelectricity by Ultraviolet Raman Spectroscopy

Abstract

We demonstrated that ultraviolet Raman spectroscopy is an effective technique to measure the transition temperature ( T c ) in ferroelectric ultrathin films and superlattices. We showed that one-unit-cell-thick BaTiO 3 layers in BaTiO 3 /SrTiO 3 superlattices are not only ferroelectric (with T c as high as 250 kelvin) but also polarize the quantum paraelectric SrTiO 3 layers adjacent to them. T c was tuned by ∼500 kelvin by varying the thicknesses of the BaTiO 3 and SrTiO 3 layers, revealing the essential roles of electrical and mechanical boundary conditions for nanoscale ferroelectricity.

Multi-ferroic and magnetoelectric materials and interfaces

“…Moreover, it was believed that the critical thickness for ferroelectricity in thin films is much larger than the thickness necessary for tunnelling to take place. The discovery of ferroelectricty in ultrathin films [153][154][155][156] opened the exciting prospect for FTJs, in which an FE thin film is used as a barrier (figure 9b) [151].…”

An investigation on magnetism, spin–phonon coupling, and ferroelectricity in multiferroic GdMn2O5

“…3(d) and (e). The intensity is normalized by the Bose factor n + 1 = (1 − exp(− ω/kT )) −1 , where is the Plank constant, and k is Boltzmann constant, and by the intensity of the corresponding modes at ∼10 K [19]. In addition, anomalies around T N and T N 1 in the T -dependence of intensities of the two modes at ∼667 and ∼616 cm −1 can be identified, confirming the significant spin-phonon coupling.…”

Piezoelectricity in the Dielectric Component of Nanoscale Dielectric-Ferroelectric Superlattices

“…Superlattices consisting of alternating dielectric and ferroelectric oxides possess an average spontaneous polarization, even with unit-cell-scale thicknesses of the ferroelectric layer, because the electrostatic energy of the structure as a whole is reduced by polarizing the normally unpolarized dielectric [1][2][3][4]. The average polarization can exceed the bulk polarization of the ferroelectric component [1], providing a new route for the enhancement of functional properties including piezoelectricity.…”

“…Here t i and f i are the lattice parameter and the structure factor for component i (i=BaTiO 3 . For 1, the change in intensity with increasing  includes only terms proportional to…”