Uniaxial Strain Engineering of Anisotropic Phonon in Few-Layer Violet Phosphorus with High Stretchability for Polarized Sensitive Flexible Photodetector

The manifestation of mechanical phenomena in quantum materials at the macroscopic level is intricately linked to pronounced electron-electron interactions within their lattices, a relationship that becomes especially evident in low-dimensional materials. Violet phosphorous (VP), a nascent 2D material distinguished by its unique vertically aligned tubular structures, has garnered considerable attention owing to its layer-dependent electronic bandgap, exceptional carrier mobility, and robust air stability. Herein, a comprehensive exploration of the phonon modes exhibited by few-layer VP through an integrated experimental-theoretical approach, focusing on the modulation of their Raman response under the uniaxial strain along a-axis, b-axis, and tube direction, respectively, is undertaken. Density functional theory calculations highlight when strain is applied along the a- or b-axis direction, the strain is predominantly mitigated through tube rotational adaptations instead of the change of bond length and bond angle, culminating in a pronounced anisotropic Raman response. Moreover, the strain engineering can effectively optimize the photoelectric response performance of VP, including increase the responsivity ≈2500% and elevate the anisotropic ratio from 2.26 to 3.38. This investigation not only confirms the superior stretchability and impact resistance properties of cross-structured VP but also establishes the groundwork for exploring the strain-induced anisotropic optoelectric properties to VP.