Emerging Functionalities by Reversibly Controllable Defects Across Oxide Interfaces

The ability to control a variety of functionalities with external stimuli is one of the main issues in oxide heterostructures for energy and electronic applications. In particular, due to the extreme sensitivity of intriguing properties in functional oxides by chemical stimuli, the control of the deterministic defects in a reversible way is required to fully exploit emergent functionality, such as metal-insulator transition, in oxide heterostructures.<br/>Here, our research efforts are presented to demonstrate novel phenomena to reversibly control properties and to unprecedentedly achieve materials synthesis at oxide interfaces by using two functional defects (i.e., hydrogen interstitial and oxygen vacancies). First, our strategy for massive hydrogen doping in VO₂ allows to elucidate remarkable phase modulation, demonstrating two-step insulator-metal-insulator phase transition during band filling [1]; this hydrogenation was enhanced by electric-field across the solid-solid interfaces [2] and vertically aligned domain boundaries [3]. Secondly, directional oxygen ionic transfer assisted by oxygen vacancies from VO₂ to TiO₂ unprecedentedly stabilized high-quality epitaxial TiO₂ films with rutile phase at the lowest temperature (&lt; 150 °C) ever reported, at which rutile phase is difficult to be crystallized [4]. Our findings show robust control of defect-induced properties at oxide interfaces, and suggests a novel synthetic strategy to overcome a kinetic barrier to phase stabilization by ionic transfer at exceptionally low temperature.<br/>This work was performed in collaboration with Dr. Yunkyu Park, Dr. Hyojin Yoon, Dr. Minguk Jo, Dr. Jaeseoung Park, Hyeji Sim, Dr. Gi-Yeop Kim, Dr. Daseob Yoon, Dr. Hyeon Han, Dr. Younghak Kim, Dr. Kyuwook Ihm, Dr. Kyung Song, Prof. Jong-Kyu Kim, Prof. Minseok Choi, Prof. Ji-Young Jo, Prof. Donghwa Lee and Prof. Si-Young Choi.<br/>[1] H. Yoon <i>et al.</i>, <i>Nature Mater.</i> <b>15</b>, 1113 (2016)<br/>[2] M. Jo <i>et al.</i>, <i>Adv. Funct. Mater. </i><b>28</b>, 1802003 (2018)<br/>[3] J. Park <i>et al., ACS Nano </i><b>14</b>, 2533 (2020)<br/>[4] Y. Park <i>et al., Nature Commun. </i><b>11</b>, 1401 (2020)