Chelant-enhanced solution for wafer-scale synthesis of few-layer WS₂ films

Abstract: Large area growth of few-layer transitional-metal dichalcogenide thin films using a solution-based process are being considered as potentially scalable thin-film processing for future nanoelectronics. A wafer-scale growth of two-dimensional tungsten disulfide (WS₂) films with consistent uniformity still remains a challenge in all types of growth methods. Specifically, the synthesis of WS₂ using a solution-based approach has been a difficult task due to the complex surface chemistry involved. In the current study, we report on the wafer-scale synthesis of uniform WS₂ using a spin-coat process. Previously, a solvent of ethylenediaminetetraacetic acid in DMSO with ammonium tetrathiomolybdate ((NH₄)₂MoS₄), and a thermolysis step were used to achieve uniform wafer-scale growth of few-layer MoS₂ films. Here, we present a study of three different chelating agents using dimethyl sulfoxide (DMSO) as a solvent to demonstrate the chelant’s critical role in growing uniform dichalcogenide films. Of these three chelating agents, glycine consistently produced wafer-scale growth. Impact statement: Although graphene is compatible with many current technologies taking advantage of its physical properties, its lack of a bandgap limits its current applications for mainstream electronics. Transition-metal dichalcogenides (TMDs) have been studied well in the past decade, with a tremendous amount funding from federal agencies and the industry, and have demonstrated multiple avenues to modulate their electronic properties, including bandgap and conductivity. Advances in growth of two-dimensional materials enable us to deposit layered materials that are only one or few unit cells in thickness, and enabled us to fabricate novel devices. However, to realize their mainstream applications in electronics, a scalable method to develop high-quality wide-area films is necessary. Research on solution-based TMD growth has investigated the effects of different solvent systems, including additives such as polymers as dispersants and adhere the precursors to the substrate. However, these methods tend to produce rather inhomogeneous films. In this article, we propose a solution-based chelant-enhanced WS₂ TMD growth method that takes advantage of the metal precursor’s complexation normally parasitic to film growth, resulting in higher-quality few-layer films. Our method offers the next step in wafer-scale TMD films that is necessary for incorporating them into semiconductor industry compatible processing. Graphical abstract: [Figure not available: see fulltext.]