HBN Encapsulation Effects on the Phonon Modes of MoS2 with a Thickness of 1 to 10 Layers

Abstract

AbstractInterfaces with surrounding materials, where charged impurities and surface roughness are present, have a significant impact on the electrical and optical properties of 2D materials. In the change of the phonon modes of MoS2 accompanied by thickness variation, the portion caused by intrinsic factors and the portion caused by the interface effect are separated by examining the result of encapsulation with hexagonal boron nitride (hBN). For instance, the frequency of the A1g peak of MoS2 supported by SiO2 decreases by ≈4 cm−1 in air for a thickness reduction from ten layers to monolayer. Of this decrease, roughly 2 cm−1 is attributable to the weakening of the van der Waals interlayer interaction, while the remaining 2 cm−1 is due to the interface effect. The interface state, that is, the types and concentrations of impurities at the interface, between MoS2 and SiO2 is estimated to be similar to that between MoS2 and air because the Raman properties when one surface of MoS2 is in contact with SiO2 and with air are identical within the measurement error. When entirely encapsulated with hBN, the width of the A1g peak of few‐layer MoS2 is significantly reduced, becoming comparable or equal to that of bulk MoS2.