We demonstrate that ultraviolet Raman spectroscopy is an effective technique to measure the transition temperature, Tc, accurately in ferroelectric ultrathin films and superlattices. We show that one-unit-cell thick BaTiO3 layers in BaTiO3/SrTiO3 superlattices are not only ferroelectric (Tc as high as 250 K), but also polarize the quantum paraelectric SrTiO3 layers adjacent to them. Tc was tuned by ~ 500 K by varying the thicknesses of BaTiO3 and SrTiO3 layers, revealing the essential roles of electrical and mechanical boundary conditions for nanoscale ferroelectricity.
Tenne, Dmitri; Bruchhausen, A.; Lanzillotti-Kimura, N. D.; Fainstein, A.; Katiyar, R. S.; Cantarero, A.; and Soukiassian, A.. (2006). "Probing Nanoscale Ferroelectricity by Ultraviolet Raman Spectroscopy". Science, 313(5793), 1614-1616. http://dx.doi.org/10.1126/science.1130306