Small Molecule Inhibitor-Modulated Al₂O₃ Atomic Layer Deposition on Monolayer MoS₂ for Controlled Nucleation

The integration of ultrathin dielectrics on two-dimensional (2D) semiconductors is essential for advancing beyond-Si electronics. However, the intrinsic inertness of van der Waals 2D basal planes remains a primary bottleneck to achieving uniform dielectric nucleation and growth. Here, we introduce a small molecule inhibitor (SMI)-modulated thermal atomic layer deposition (ALD) strategy, exemplified by aluminum oxide (Al₂O₃) ALD on monolayer molybdenum disulfide (1L MoS₂) with acetic acid (HAc) SMI. The ABC-type sequence comprises HAc inhibitor (A), trimethylaluminum (TMA) precursor (B), and deionized H₂O coreactant (C). In situ quartz crystal microbalance (QCM) studies reveal robust HAc adsorption on Al₂O₃ and suppression of subsequent oxide growth on HAc-passivated surfaces. When applied to 1L MoS₂, this inhibitory pathway enables HAc to selectively passivate nascent Al₂O₃ nuclei formed on the MoS₂ surface, limiting their three-dimensional (3D) island coarsening and redirecting precursor adsorption toward the uncovered basal plane. Consequently, nearly continuous ultrathin (∼1.5 nm) Al₂O₃ films are achieved on 1L MoS₂ with markedly improved uniformity compared to standard Al₂O₃ ALD using TMA and H₂O, as validated by atomic force microscopy (AFM), cross-sectional scanning transmission electron microscopy (STEM), and energy-dispersive X-ray spectroscopy (EDS). Density functional theory (DFT) calculations further provide atomistic insight into HAc-modulated Al₂O₃ nucleation, corroborating the energetic preference of HAc for Al₂O₃ over MoS₂ and attenuated TMA adsorption on HAc-passivated surfaces. Spatially resolved Raman spectroscopy also confirms that the HAc-modulated process preserves the structural integrity of 1L MoS₂, with only minimal strain and doping perturbations observed after dielectric deposition. This SMI-modulated approach offers a broadly applicable framework for controlling ALD nucleation across various inhibitors, ALD chemistries, and 2D materials, opening opportunities for reliable dielectric integration in next-generation nanoelectronics.