Park Jaeseoung, Yoon Hyojin, Sim Hyeji, Choi Si-Young, Son Junwoo
Department of Materials Science and Engineering , Pohang University of Science and Technology (POSTECH) , Pohang 37673 , Republic of Korea.
ACS Nano. 2020 Feb 25;14(2):2533-2541. doi: 10.1021/acsnano.0c00441. Epub 2020 Feb 14.
Electronic phase modulation based on hydrogen insertion/extraction is kinetically limited by the bulk hydrogen diffusion or surface exchange reaction, so slow hydrogen kinetics has been a fundamental challenge to be solved for realizing faster solid-state electrochemical switching devices. Here we accelerate electronic phase modulation that occurs by hydrogen insertion in VO through vertically aligned 2D defects induced by symmetry mismatch between epitaxial films and substrates. By using domain-matching epitaxial growth of monoclinic VO films with lattice rotation and twinning on hexagonal AlO substrates, the domain boundaries naturally align vertically; they provide a "highway" for hydrogen diffusion and surface exchange in VO films and overcome the limited rates of bulk diffusion and surface reaction. From the quantitative analysis of the deuterium (H) isotope tracer exchange, it is confirmed that the tracer diffusion coefficient () and surface exchange coefficient () were increased by several orders of magnitude in VO films that had domain boundaries. These results yield fundamental insights into the mechanism by which mobile ions are inserted along extended defects and provide a strategy to overcome a limitation to switching speed in electrochemical devices that exploit ion insertion.
基于氢嵌入/脱出的电子相位调制在动力学上受到体相氢扩散或表面交换反应的限制，因此缓慢的氢动力学一直是实现更快的固态电化学开关器件需要解决的一个基本挑战。在此，我们通过外延薄膜与衬底之间的对称性失配所诱导的垂直排列二维缺陷，加速了VO中因氢嵌入而发生的电子相位调制。通过在六方AlO衬底上利用具有晶格旋转和孪晶的单斜VO薄膜的畴匹配外延生长，畴界自然垂直排列；它们为VO薄膜中的氢扩散和表面交换提供了一条“高速公路”，并克服了体相扩散和表面反应的有限速率。通过对氘（H）同位素示踪剂交换的定量分析，证实了在具有畴界的VO薄膜中，示踪剂扩散系数（）和表面交换系数（）提高了几个数量级。这些结果为移动离子沿扩展缺陷插入的机制提供了基本见解，并提供了一种策略来克服利用离子插入的电化学器件中开关速度的限制。
