Direct Observation of Dipole Formation Triggered by Interlayer Sliding at Atomic Level in Semimetal MoTe₂

Area of Science:

• Materials Science
• Condensed Matter Physics
• Nanotechnology

Background:

• Octahedral molybdenum ditelluride (MoTe2) exhibits a nonpolar 1T' phase that transitions to a polar Td phase around 260 K.
• The exact mechanism of polarization formation via interlayer sliding during cooling remains unclear due to challenges in atomic-resolution imaging.

Purpose of the Study:

• To investigate the atomic-scale mechanism of interlayer sliding and polarization formation in van der Waals-layered MoTe2.
• To elucidate the role of cooling on phase transitions and stacking order in MoTe2.

Main Methods:

• In situ cryogenic scanning transmission electron microscopy (cryo-(S)TEM) was employed to capture atomic-level details.
• Observation of interlayer sliding and domain formation during cooling from 300 K down to 110 K.

Main Results:

• Step-by-step formation of local Td domains within the 1T' phase was observed between 300 K and 193 K.
• Disordered mixed stacking of 1T'/Td phases was visualized at 110 K.
• Sliding energy barriers of 2.7 and 5.3 meV/u.c. were calculated, indicating thermally accessible sliding.

Conclusions:

• The study provides atomic-scale insights into the sliding-induced polarization mechanism in MoTe2.
• Findings offer significant implications for the design and development of sliding ferroelectric-based nonvolatile memory devices.