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

Abstract

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 σ_IR/d², showing strong correlation with P_s (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.