Sohn Woonbae, Kim Taemin Ludvic, Lee Tae Hyung, Yoon Sangmoon, Kim Chungsoo, Yoo Jung-Woo, Roh Kwang Chul, Kim Miyoung, Jang Ho Won
Department of Materials Science and Engineering, Research Institute of Advanced Materials, Seoul National University, Seoul 08826, Republic of Korea and Energy Storage Materials Centre, Korea Institute of Ceramic Engineering and Technology, Jinju 52851, Republic of Korea.
Department of Materials Science and Engineering, Research Institute of Advanced Materials, Seoul National University, Seoul 08826, Republic of Korea.
Nanoscale. 2021 Jan 21;13(2):708-715. doi: 10.1039/d0nr07545k.
A quasi-two-dimensional electron gas (2DEG) evolved at the LaAlO3 (LAO)/SrTiO3 (STO) interface has attracted significant attention, because the insertion of perovskite titanates can tune the 2DEG conductivity. However, this depends on the Ti-O-Ti bonding angle and structural symmetry. In this study, we controlled the octahedral tilt of the LAO/CaTiO3 (CTO) interface by heterostructuring it with CTO grown on STO substrates of various thicknesses. The 2DEG was maintained when the thickness of CTO was below the critical thickness of 5 unit cells (uc); however, it was suppressed when the CTO thickness was above the critical thickness. High-angle annular dark-field (HAADF) scanning transmission electron microscopy (STEM) combined with integrated differential phase contrast (iDPC) STEM imaging was used to visualize the TiO6 octahedral tilt propagation and symmetry of the 5 uc and 24 uc CTO films. The symmetry of the 5 uc CTO film resembled that of the STO substrate, whereas the octahedral tilt propagated in the 24 uc CTO film due to the structural relaxation. These results show that the interface engineering of the octahedral tilt can enable or suppress the formation of the 2DEG in perovskite oxides.
在LaAlO3（LAO）/SrTiO3（STO）界面处演化出的准二维电子气（2DEG）引起了广泛关注，因为钙钛矿钛酸盐的插入可以调节2DEG的电导率。然而，这取决于Ti-O-Ti键角和结构对称性。在本研究中，我们通过在不同厚度的STO衬底上生长CTO对LAO/CaTiO3（CTO）界面的八面体倾斜进行了控制。当CTO的厚度低于5个晶胞（uc）的临界厚度时，2DEG得以维持；然而，当CTO厚度高于临界厚度时，2DEG受到抑制。使用高角度环形暗场（HAADF）扫描透射电子显微镜（STEM）结合积分差分相衬（iDPC）STEM成像来观察5 uc和24 uc CTO薄膜中TiO6八面体倾斜的传播和对称性。5 uc CTO薄膜的对称性与STO衬底相似，而由于结构弛豫，八面体倾斜在24 uc CTO薄膜中传播。这些结果表明，八面体倾斜的界面工程可以实现或抑制钙钛矿氧化物中2DEG的形成。
