Fig. 3
From: Artificial two-dimensional polar metal by charge transfer to a ferroelectric insulator
Structural, elemental, and electronic characterization of a LaAlO3/Ba0.2Sr0.8TiO3/SrTiO3heterostructure. a, b The heterostructure has 15 unit cells (uc) of LaAlO3 (LAO) and 10 unit cells of Ba0.2Sr0.8TiO3 (BST) on SrTiO3 (STO) substrate. Atomically resolved inverted annular-bright-field scanning transmission electron microscopy (ABF-STEM) images of the LAO/BST interface (a) and BST/STO interface (b), respectively. The orange dashed squares focus on regions which are representative unit cells of LAO, the LAO/BST interface, the BST/STO interface and STO, respectively, and are enlarged for clearer view. The brighter atomic columns in the corner are A-site (Sr, Ba, La) columns and the darker columns at/near the center are B-site (Ti, Al) columns. c Out-of-plane B-OII and A-OI displacements across the LAO/BST/STO heterostructure. d High-angle annular dark-field (HAADF) STEM image and electron energy loss spectroscopy (EELS) spectrum images of La M4,5 (yellow), Ba M4,5 (blue), Ti L2,3 (green), and O K (red) edges. BO2 layers are numbered from bottom to top. e Layer-resolved Ti L2,3 spectra. Reference spectra for Ti4+ (red) and Ti3+ (blue) are shown at the bottom, taken from SrTiO3 and Ti2O3/Al2O3, respectively. f Layer-resolved O K spectra, which are normalized by their respective main peaks near 535 eV. g Layer-resolved Ti3+ fraction (orange), which is defined as Ti3+/(Ti3+ + Ti4+), and ΔE from the O K edge (olive). The purple shaded area indicates the approximate location of the 2DEG. e–g are all aligned with the HAADF image and EELS spectra in d. The error bars show the standard deviations of the averaged measurements for each vertical atomic layer
