Large-scale synthesis of monolayer WS2by low-temperature sulfurization of oxidized magnetron sputtered monolayer W precursors in a microreactor

Abstract

We report large-scale synthesis of monolayer WS₂films obtained by sulfurization of oxidized magnetron sputtered monolayer W precursors. Literature routes typically require ∼ 800°C, well above the 400°C limit imposed by back-end-of-line (BEOL) integration. Here, using an enhanced chemical vapor deposition (CVD) approach, the magnetron sputtered ultrathin W precursor (a W monolayer film, 0.27 nm thick, which in ambient air becomes a WO_xmonolayer) is sulfurized at the lowest possible temperature (450 °C) within a microreactor, which consists of a sandwich-like structure formed by the precursor and a clean Si substrate. The obtained WS₂material has a good crystallinity and uniform morphology across the entire growth substrate, as confirmed by detailed characterization. These results highlight the versatility of the method combining magnetron sputtering and microreactor-CVD, facilitating its applications to wafer-scale synthesis of monolayer WS₂, heterogeneously integrated into electronic circuits (a major objective for next-generation electronics and optoelectronics). Additionally, we investigate in detail the properties of WS₂films synthesized from a bilayer W precursor (0.43 nm thick), under the same conditions, and we calculated the frequencies of the second-order Raman scattering modes. For electrical measurements, we fabricated WS₂/few-layer-graphene heterostructures, whose atomically clean interface yields reliable, low-resistance contacts. These devices exhibit resistive switching behavior, likely governed by vacancy migration, making it a promising candidate for memristive applications. Our results demonstrate that electronics-grade monolayer WS₂can be synthesized at 450°C, approaching the BEOL requirement of 400°C.

Keywords: 2D layered materials; BEOL; microreactor; transition metal dichalcogenide.