Rapid nucleation of ZnO on MoS₂ and WS₂ using an atmospheric-pressure spatial atomic layer deposition system

Abstract Uniform deposition of metal oxides on 2D materials, while preserving their structural integrity, is a crucial step to realize the integration of 2D materials in practical devices. In this study, we demonstrate the rapid nucleation of ZnO using atmospheric-pressure spatial chemical vapor deposition (AP-SCVD) on 2D transition metal dichalcogenides MoS₂ and WS₂. The high precursor partial pressure and uniform precursor delivery afforded by the AP-SCVD process, as compared to conventional atomic layer deposition (ALD), led to rapid ZnO nucleation on both CVD-grown MoS₂ and WS₂ in as little as 5 AP-SCVD oscillations and complete film closure was achieved on CVD-grown WS₂ flakes in less than 60 AP-SCVD oscillations. The ZnO nuclei formed larger interconnected clusters on MoS₂, whereas more-isolated islands were formed on the WS₂. Raman and photoluminescence (PL) spectroscopy revealed that AP-SCVD is a benign process that does not damage the underlying 2D materials and rather helps to passivate defects via oxygen/water adsorption from the air, when performed in an appropriate temperature window. Deposition of the ZnO was found to impact the optical and structural properties of CVD-grown MoS₂ and WS₂ differently. For the MoS₂–ZnO heterostructure, electron doping and strain dominate, resulting in a reduction in the PL of MoS₂, whereas for the WS₂–ZnO, strain and dielectric screening have a larger impact, resulting in an enhanced PL.