Structure and Characteristics of Few-layer Molybdenum Disulfide

Abstract

ABSTRACTLayered transition-metal dichalcogenides such as molybdenum disulfide are indirect band gap materials in their bulk form but become direct semiconductors when pared down to a single layer. This paper discusses the structural characteristics and properties of single and few-layer molybdenum disulfide. Specifically, we present aberration-corrected high-resolution transmission electron microscopy (HRTEM) investigations of the structural properties of this material. This information is augmented with data from Raman and photoluminescence spectroscopies on single and few-layer samples. High-resolution TEM images of few-layer and bulk molybdenum disulfide confirm a hexagonal structure for the material. Direct images, along with corresponding fast Fourier transforms, provide valuable information about the crystal structure and reciprocal space lattice of few-layer molybdenum disulfide. One can, for example, determine the in-plane lattice constants experimentally from analysis of the TEM images. Atomic force microscope topographic maps can yield the thickness of a monolayer of molybdenum disulfide; these maps can also be used to determine the thicknesses of multi-layered samples. Analysis of combined Raman and photoluminescence spectroscopy data are valuable in confirming the number of layers in molybdenum disulfide samples. Furthermore, the photoluminescence data can provide unique information on the nature of emission from monolayer molybdenum disulfide; it is characteristically different from that of few-layer samples. The spectral location of the monolayer peak emission agrees with what was obtained from theoretical calculations.