Intra-interlayer competition: a key regulator for sliding ferroelectricity in hydrogen-functionalized group-III monochalcogenide monolayer.

Sliding ferroelectricity, an emerging mechanism generating out-of-plane polarization via interlayer sliding, has greatly expanded the scope of 2D ferroelectrics. The current design of sliding ferroelectricity primarily relies on stacking homogeneous/heterogeneous 2D vdW materials, while this work demonstrates that bilateral hydrogenation can induce sliding ferroelectricity in III-VI monolayers, thereby further expanding the scope of ferroelectric materials. Furthermore, we provide fundamental mechanism insights into hydrogenation-induced sliding ferroelectricity. This study systematically investigates the structural reconstruction and the mechanism for inducing sliding ferroelectricity in monolayer group-III monochalcogenides MX (M = Ga, In; X = S, Se, Te), via bilateral hydrogen functionalization, employing first-principles calculations. It is found that hydrogen atoms preferentially and stably adsorb onto the chalcogen atom sites, reconstructing the monolayer into a bilayer-like structure and introducing interlayer sliding degrees of freedom. Thermodynamic and kinetic stability criteria confirm the stability of MX(H@X). Electronic structure analysis reveals significant out-of-plane sliding ferroelectricity under AB/BA stacking. Notably, GaTe(H@Te) exhibits an anomalous synergistic effect characterized by high polarization and a low energy barrier. Mechanism studies indicate that the ferroelectricity is governed by a competition mechanism between intralayer M-X bonding and interlayer coupling (M-M/M-X interactions). Strain modulation of structural parameters (d1, d2, l) enabled the construction of a descriptor d1l/d2, which accurately correlates with polarization changes. Elemental dependency analysis led to the descriptor σIR/d2, showing strong correlation with Ps (R2 = 0.95), revealing a synergistic effect of weakened intralayer competition and enhanced interlayer coupling. This work proposes surface hydrogen functionalization as a novel strategy for inducing sliding ferroelectricity, offering advantages of high targetability and efficiency compared to traditional van der Waals stacking methods, thereby providing a theoretical basis for expanding the sliding ferroelectric material system and designing high-performance devices.