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. 2017 May 19;7:2160. doi: 10.1038/s41598-017-02113-4

Figure 3.

Figure 3

Main optical modes contributing to the large static dielectric constant for STO bulk (top) and for a slab of 7 layers under −1.305% strain (bottom). The bulk TO modes are represented as black and red sticks. Meanwhile, only the large LO-TO shift for the TO1 mode (shift ~700 cm) is illustrated with a red arrow. At the bottom of the figure, the main optical modes for a 7 layers slab under −1.305% strain are presented. The black sticks represent modes which derive their intensities from atoms further from the surfaces (bulk like modes). The blue sticks are transverse modes from atoms at the TiO2-terminated surface. The red stick at 210 cm−1 corresponds to a TO mode from Ti-O bending (bulk like mode). The very large LO-TO shift of the 210 cm−1 mode (indicated by a red arrow) contributes strongly to the high value of ε(0)//. Insets top and bottom: the elementary cell for bulk and for 7 layers slab (Sr: big green sphere, Ti: medium blue sphere, O: small red sphere).