Monolayer MoS₂ With Ultrahigh Piezoelectricity: From ALD Dose Control to Device Performance

A critical challenge in the controllable atomic layer deposition (ALD) synthesis of functional two-dimensional materials is understanding how early-stage ultrathin film states govern the final material and device characteristics. Herein, using ALD of MoO_x followed by sulfurization, we show that the precursor dosages effectively control the quality of the as-deposited oxide film and thereby govern the subsequent oxide-to-monolayer conversion pathway of MoS₂. By tuning the ALD dose, the film growth evolves from isolated flakes to porous monolayers and ultimately to continuous monolayers. Comparative structural, chemical, and electronic analyses reveal that the optimized continuous monolayer exhibits higher continuity, lower defect density, improved stoichiometry, and reduced free-charge screening. As a result, the MoS₂ monolayer delivers an effective piezoelectric coefficient $d_{11}^{\mathrm{eff}}$ of 4.3 pm V^-1, while the linear sensitivity of 326.9 mV and 141.38 pA per 1% lateral strain is highest among binary transition metal dichalcogenides. The optimized films also enable proof-of-usability demonstrations in wearable sensing and closed-loop slippage feedback control. These results establish an oxide-state-controlled growth framework for engineering continuous low-screening piezoelectric monolayers and provide a practical route toward high-performance flexible electromechanical devices.