  Two-dimensional (2D) Fe-chalcogenides have emerged with rich structures,
magnetisms and superconductivities, which sparked the growing research
interests in the torturous transition mechanism and tunable properties for
their potential applications in nanoelectronics. Uniaxial strain can produce a
lattice distortion to study symmetry breaking induced exotic properties in 2D
magnets. Herein, the anomalous Raman spectrum of 2D tetragonal (t-) and
hexagonal (h-) FeTe were systematically investigated via uniaxial strain
engineering strategy. We found that both t- and h-FeTe keep the structural
stability under different uniaxial tensile or compressive strain up to +/-
0.4%. Intriguingly, the lattice vibrations along both in-plane and out-of-plane
directions exceptionally hardened (softened) under tensile (compressive)
strain, distinguished from the behaviors of many conventional 2D systems.
Furthermore, the difference in thickness-dependent strain effect can be well
explained by their structural discrepancy between two polymorphs of FeTe. Our
results could provide a unique platform to elaborate the vibrational properties
of many novel 2D materials.
