Millimeter-Scale Continuous Film of MoS2 Synthesized Using a Mo, Na, and Seeding Promoter-Based Coating as a Solid Precursor.

While the chemical vapor deposition technique can be used to fabricate 2D materials in a larger area, materials like MoS2 have limited controllability due to their lack of self-controlling nature. This article presents a new technique for synthesizing a void-free millimeter-scale continuous monolayer MoS2 film through the diffusion of a well-controlled Mo, Na, and seeding promoter-based coating under a low-pressure N2 atmosphere. Compared to the conventional method, this technique provides precise control of solid precursors, where MoS2 grows next to the coating. At 800 °C, the synthesized MoS2 showed a uniform single-layer MoS2 film; however, a Na-free coating showed nanoscale voids and poor crystal quality, which are attributed to a higher edge-attachment barrier that slows down the MoS2 lateral growth. The synthesized MoS2 with Na-containing solution showed an intense PL peak with a 1.86 eV band gap. Even at the relatively low temperature of 700 °C, compared to the Na-excluded condition, MoS2 showed almost two times higher area coverage with a comparatively larger crystal size. This finding may assist in the future development of MoS2-based electronic and optoelectronic devices such as transistors and photodetectors.

Selective growth of monolayer and bilayer graphene patterns by a rapid growth method.

The use of next-generation graphene requires the control of the number of deposition layers together with its fast synthesis for its use in advanced and miniaturized devices. Here, this article describes a novel technique for the selective growth of a continuous film of a graphene pattern (controlled monolayer/multilayer design) by the chemical vapor deposition (CVD) method on Cu foils modified by different plasma treatments. Ex situ Ar plasma treatment is the preferred treatment for monolayer graphene (I2D/IG = 1.81) synthesis. Bilayer graphene (I2D/IG = 1.05) growth was influenced by applying an additional oxygen plasma treatment, which led to different morphologies and control of the surface-active nature of Cu. The required design was achieved by a photolithography process. Graphene synthesis was performed by a short annealing process (60 s) followed by a single-step short burst of graphene growth (60 s). Relatively high density graphene nuclei with faster graphene growth resulted in monolayer graphene in the Ar plasma-treated area. Ex situ oxygen plasma treatment in selected areas was capable of controlling the amount of graphene nuclei formation, while the kink structure was capable of bolstering the adsorption of a relatively high amount of carbon adatoms, resulting in bilayer graphene.