Formation mechanism of twin domain boundary in 2D materials: The case for WTe2

摘要

Our scanning tunneling microscopy (STM) study observes,for the first time,twin domain boundary (TDB) formations on the surface of WTe2 single crystal,which is glued by solidifying indium to Si substrate.In these TDB regions,a large inhomogeneous strain field,especially a critical shear strain of about 7％,is observed by geometric phase analysis.This observation does not obey the old believe that a small mechanical stress is sufficient to drive thermally-induced TDB formations in two-dimensional materials.To resolve the contradiction,we perform density functional theory calculations combined with elasticity theory analysis,which show that TDBs on WTe2 are entirely displacement-induced,for which a critical strain is necessary to overcome the onset barrier.