Anisotropic Ion Migration and Electronic Conduction in van der Waals Ferroelectric CuInP2S6

Dawei Zhang, Zheng-Dong Luo, Yin Yao, Peggy Schoenherr, Chuhan Sha, Ying Pan, Pankaj Sharma, Marin Alexe, Jan Seidel

Research output: Contribution to journalArticlepeer-review

66 Citations (Scopus)


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 (CuInP2S6) 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.

Original languageEnglish
Pages (from-to)995-1002
Number of pages8
JournalNano Letters
Issue number2
Publication statusPublished - 27 Jan 2021
Externally publishedYes


  • copper indium thiophosphate
  • ion migration
  • ionic conduction
  • van der Waals ferroelectrics


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