Zhang Dawei, Luo Zheng-Dong, Yao Yin, Schoenherr Peggy, Sha Chuhan, Pan Ying, Sharma Pankaj, Alexe Marin, Seidel Jan
School of Materials Science and Engineering, UNSW Sydney, Sydney, NSW 2052, Australia.
Department of Physics, The University of Warwick, Coventry CV4 7AL, United Kingdom.
Nano Lett. 2021 Jan 27;21(2):995-1002. doi: 10.1021/acs.nanolett.0c04023. Epub 2021 Jan 6.
Van der Waals (vdW) thio- and seleno-phosphates have recently gained considerable attention for the use as "active" dielectrics in two-dimensional/quasi-two-dimensional electronic devices. Bulk ionic conductivity in these materials has been identified as a key factor for the control of their electronic properties. However, direct evidence of specific ion species' migration at the nanoscale, particularly under electric fields, and its impact on material properties has been elusive. Here, we report on direct evidence of a phase-selective anisotropic Cu-ion-hopping mechanism in copper indium thiophosphate (CuInPS) through detailed scanning probe microscopy measurements. A two-step Cu-hopping path including a first intralayer hopping (in-plane) and second interlayer hopping (out-of-plane) crossing the vdW gap is unveiled. Evidence of electrically controlled Cu ion migration is further verified by nanoscale energy-dispersive X-ray spectroscopy (EDS) mapping. These findings offer new insight into anisotropic ionic manipulation in layered vdW ferroelectric/dielectric materials for emergent vdW electronic device design.
范德华硫代磷酸盐和硒代磷酸盐最近在二维/准二维电子器件中作为“活性”电介质的应用方面受到了广泛关注。这些材料中的体离子电导率已被确定为控制其电子性质的关键因素。然而，特定离子种类在纳米尺度上迁移的直接证据，特别是在电场作用下的迁移及其对材料性质的影响，一直难以捉摸。在此，我们通过详细的扫描探针显微镜测量，报告了硫代磷酸铜铟（CuInPS）中相选择性各向异性铜离子跳跃机制的直接证据。揭示了一条两步铜跳跃路径，包括第一步层内跳跃（面内）和第二步层间跳跃（面外），跨越范德华间隙。纳米级能量色散X射线光谱（EDS）映射进一步验证了电控铜离子迁移的证据。这些发现为新兴范德华电子器件设计中分层范德华铁电/介电材料的各向异性离子操纵提供了新的见解。
