Ultraclean and Direct Transfer of a Wafer-Scale MoS2 Thin Film onto a Plastic Substrate

Abstract

A direct transfer method was developed using epoxy glue as an exfoliating substance to detach MoS2 film from the growth substrate and to allow its easy transfer onto a flexible substrate. By using this method, wafer-scale MoS2 films with various thicknesses can be transferred onto a flexible substrate almost perfectly without defects such as cracks, wrinkles, or contaminants. The wafer-scale MoS2 mono- to trilayer film was synthesized in a custommade CVD chamber in a low pressure state. First, the SiO2 substrate was cleaned using sonication for 10 min each in acetone and isopropyl alcohol, and then rinsed twice in deionized water. To grow the film, a mass of 5 mg molybdenum trioxide (MoO3) in a quartz boat was placed at the center of the furnace, and the SiO2 substrate was placed downstream from the MoO3 powder. The furnace was heated up to 600°C at a rate of 20°C min-1 under Ar gas with a flow rate of 200 sccm. H2S gas with a flow rate of 1 sccm was injected into the chamber to sulfurize MoO3 over the course of 30 min. The CVD-MoS2 film was transferred from either the sapphire or SiO2/Si substrate onto a PET plastic substrate by using epoxy glue. For the transfer process, we first mixed 2 g of an epoxy chemical with 2 g of a hardener chemical. This mixture was then placed in a vacuum chamber for 25 min to remove bubbles created during the mixing. We then administered the epoxy glue to a piece of PET plastic on a hot plate set at 50°C, and the epoxy became soft, and spread flat to cover the PET. Then, MoS2 attached to the sapphire or SiO2/Si substrate was placed face down onto the epoxy glue and moved around to remove bubbles trapped between the surfaces of the substrate and epoxy glue. Use of this one-step process was found to preserve the ultraclean surface of the growth substrate without chemical residue produced during wet etching processes. Since, when using this method, no residual materials remain on the growth substrate, the substrate may be recycled for synthesis.