High-κ samarium oxysulfate dielectric for two-dimensional electronics with enhanced gate coupling

Layered dielectric materials and their van der Waals (vdW) heterostructures offer high potential for next-generation two-dimensional (2D) electronic devices, but materials that combine a wide bandgap and high dielectric constant are rare. Here, we present the controllable synthesis of quasi-vdW layered samarium oxysulfate (Sm 2 O 2 SO 4 ) single crystals via a molten-salt-assisted chemical vapor deposition (CVD) method. These atomically thin crystals exhibit remarkable dielectric properties, including a wide bandgap (~5.54 eV), high dielectric constant (~18), robust breakdown voltage (>12 MV cm -1 ) and good thermal reliability. By integrating ultrathin Sm 2 O 2 SO 4 nanoplates with 2D molybdenum disulfide (MoS 2 ) via vdW forces, we fabricate field-effect transistors (FETs) showing a subthreshold swing down to 65.2 mV dec -1 , hysteresis down to 5.4 mV, on/off current ratios of ~10 9 , and gate leakage currents down to around 7 × 10 -7  A cm -2 . Furthermore, a high gate coupling ratio (GCR ~ 0.83) non-volatile memory device was developed based on the MoS 2 /h-BN/MLG/Sm 2 O 2 SO 4 /MLG heterostructure. The flash memory achieves ultrafast (~50 ns) programming/erasing operations, robust endurance (>2000 cycles) and long-term retention (>10 years). This work shows promising results for the integration of Sm 2 O 2 SO 4 as a high- κ dielectric in future 2D devices, with implications for low-power, high-performance electronics.