Direct Observation of Dipole Formation Triggered by Interlayer Sliding at Atomic Level in Semimetal MoTe.

Octahedral MoTe is a nonpolar 1T' phase and transforms into polar T phase at ∼260 K, along with the change of the layer stacking order. However, as it is difficult to capture the interlayer sliding at atomic resolution, the polarization formation mechanism of MoTe by cooling to low temperature remains largely unclear. Here, we address the challenge by in situ cryo-(S)TEM to trace the interlayer sliding at the atomic level and the induced polarization in vdW-layered MoTe. When it is in the range of 300-193 K, we observed the step-by-step formation of the local T domain within the 1T'-I domain. Moreover, we present an atomic-scale observation of the disordered mixed stacking of 1T'/T phases at 110 K. Two possible sliding models are built with the sliding energy barriers (2.7 and 5.3 meV/u.c.), indicating thermally accessible sliding behavior. Our investigation of sliding-induced polarization provides meaningful insights for developing sliding ferroelectric-based nonvolatile memory devices.