Probing nanoscale ferroelectricity by ultraviolet Raman spectroscopy

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 BaTiO3 layers in BaTiO3/ SrTiO3 superlattices are not only ferroelectric (with T-c as high as 250 kelvin) but also polarize the quantum paraelectric SrTiO3 layers adjacent to them. T-c was tuned by similar to 500 kelvin by varying the thicknesses of the BaTiO3 and SrTiO3 layers, revealing the essential roles of electrical and mechanical boundary conditions for nanoscale ferroelectricity.