Electric-field-driven nanoconfinement and the 5-120 nm stability regime of piezoelectric β-glycine.

Piezoelectric β-glycine is a promising molecular crystal, yet its controlled preparation remains challenging. Current nanoconfinement strategies, which rely primarily on rigid templates or simulations, cannot reliably capture the intrinsic confinement regime that leads to β-phase formation. Here, we propose electric-field-driven nanoconfinement as a one-step, continuous, and interface-free approach to investigate glycine crystallization and to define the confinement regime that yields the β-phase. We produced glycine nanoparticles via electrohydrodynamic spraying under a direct current field, automatically varying the spraying height to modulate nanoconfinement during nucleation and growth. Structural, morphological, and piezoelectric characterizations reveal that pure β-glycine forms within a crystal radius range of 5-120 nm. By integrating these findings with thermodynamic and kinetic analysis, we elucidate the mechanism of β-phase formation and construct a crystallization phase map that delineates the confinement conditions necessary for its stabilization. This work identifies the critical nanoconfinement parameters for accessing piezoelectric β-glycine and provides fundamental insights into polymorph control in molecular crystalline materials.