Dielectric Regulation in Quasi‐vdW Europium Oxysulfur Compounds by Compositional Engineering for 2D Electronics

Abstract Advancing next‐generation electronics necessitates precise control of dielectric properties in 2D materials. Here, the first synthesis of novel 2D quasi‐van der Waals (vdW) europium oxysulfur (Eu 2 SO x ) compounds, comprising hexagonal Eu₂SO₂ and tetragonal Eu₂SO₆ phases, with composition‐tunable dielectric properties, is presented. Using a homodiffusive‐controlled epitaxial growth method, materials are achieved with complementary characteristics: the hexagonal Eu₂SO₂ phase exhibits a high dielectric constant (≈30) paired with a moderate bandgap (≈4.56 eV), while the tetragonal Eu₂SO₆ phase offers a wider bandgap (≈5.62 eV) but a lower dielectric constant (≈20). The potential of these materials is demonstrated by integrating ultrathin Eu₂SO₂ nanoplates with molybdenum disulfide (MoS₂) field‐effect transistors (FETs) via vdW forces. The resulting devices achieve a near‐ideal I on / I off ratio (≈10⁸), minimal hysteresis (≈5.3 mV), a low subthreshold slope (≈63.5 mV dec⁻¹), and ultralow leakage current (≈10⁻¹⁴ A). These results highlight the capacity of europium oxysulfur compounds to address the trade‐off between dielectric constant and bandgap, offering tailored solutions for diverse 2D electronic applications. This work underscores the potential of composition engineering to expand the family of rare‐earth oxysulfur compounds for nanoelectronics, paving the way for innovative gate dielectrics in next‐generation devices.