hBN Encapsulation Effects on the Phonon Modes of MoS<sub>2</sub> with a Thickness of 1 to 10 Layers
Duk Hyun Lee, Nam‐Hee Kim, Suyong Jung, Jaesung Park, Bum-Kyu Kim, Myung‐Ho Bae, Yong Ju Yun, Sam Nyung Yi, Dong Han Ha
Abstract
Abstract Interfaces 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 MoS 2 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 A 1g peak of MoS 2 supported by SiO 2 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 MoS 2 and SiO 2 is estimated to be similar to that between MoS 2 and air because the Raman properties when one surface of MoS 2 is in contact with SiO 2 and with air are identical within the measurement error. When entirely encapsulated with hBN, the width of the A 1g peak of few‐layer MoS 2 is significantly reduced, becoming comparable or equal to that of bulk MoS 2 .