Optical and Structural Characteristics of Two Dimensional Transition Metal Dichalcogenide Materials

The optical and structural characteristics of transition metal dichalcogenides (TMDCs) such as molybdenum disulfide (MoS2), Wolfram disulfide (WS2), and Wolfram diselenide (WSe2) were studied by atomic force microscopy (AFM), photoluminescence spectroscopy (PL), and confocal second harmonic generation microscopy. CVD synthesized WS2, CVD synthesized MoS2, and micromechanically exfoliated WSe2 were used for carrying out the experiment. Structural studies on the TMDC materials confirmed the presence of monolayers with a thickness similar to 1 nm in the structure. Strong photoluminescence effect was produced from these atomically thin layer TMDC materials at an excitation wavelength 665 nm, 625 nm, and 764 nm for MoS2, WS2, and WSe2, respectively. The thinner region of these materials was produced second harmonic signals from the surface. The better luminescence effects produced from the monolayers of TMDC materials confirms the formation of TMDC monolayer from bulk materials, which causes the transition of the bandgap from indirect to direct. The PL spectrum results and information regarding SHG signals obtained from this study was very important in the aspects of the fabrication of optoelectronic devices.