Laser-induced electrochemical thinning of MoS2

Abstract

Single layers of two-dimensional metal chalcogenides, represented by molybdenum disulfide (MoS₂), have attracted wide interest due to their atomically thin structures and unique electric and optical properties. The electrical properties of MoS₂ depend on the number of layers. A single layer is a direct band-gap semiconductor exhibiting strong photoluminescence under photoexcitation, while multiple layers are indirect semiconductors. The control of the number of layers is essential for the application of MoS₂ as a two-dimensional semiconducting nanomaterial. In this work, we present a new approach to control the number of MoS₂ layers, where excitation by a laser can induce electrochemical etching of multiple layers of MoS₂. The thinning process under laser-induced etching is a self-limited reaction. Electrochemical etching becomes inactive as the number of layers is reduced, leaving a single layer or a few layers of MoS₂ on the substrate. The etched layers were characterized by Raman spectroscopy and atomic force microscopy. A field effect transistor (FET) was also fabricated to test the electrical properties of the etched MoS₂, demonstrating transistor behavior at the same threshold voltage as a multilayer MoS₂ FET.