Phase‐Controllable Synthesis and Property Modulation of Two‐Dimensional PAs ₃ S ₃ Crystal

ABSTRACT Phase engineering in two‐dimensional (2D) materials has attracted significant attention due to their richer phase structures and tunable electrical and optical properties. However, design and synthesis of distinct phase structures have been predominantly explored in atomic crystals and organic molecular crystals, while remaining highly challenging in inorganic molecular crystals (IMCs). Here we report the phase‐controllable synthesis of 2DIMC PAs 3 S 3 with Pnma and R 3 m two phases for the first time. Utilizing the kinetics‐controlled vertical microspacing sublimation (VMS) method, we found that the mass transfer efficiency is the key factor affecting the phase structure of PAs 3 S 3 . The R 3 m phase with the uniform molecular polarization direction, compared to the Pnma phase in which polarization is canceled out, exhibits a stronger second harmonic generation (SHG) signal and larger dipole–dipole interactions. PeakForce quantitative nanomechanical (PFQNM) measurements further show that the Young's modulus of the R 3 m phase (21.31 GPa) is 69% higher than the Pnma phase (12.6 GPa). Our research provides new ideas for the structural design and property modulation of 2DIMCs and demonstrates their potential applications in nonlinear optics and nano‐flexible devices.