The heating of Molybdenum diselenide, An in-situ Transmission Electron Microscopy and Density Functional Theory study

Abstract

In recent years nanomaterials have aroused a lot of interest among researchers. Nanomaterials have a wide spectrum of applications ranging from electronics to catalysis. However, much is still unknown about these nanomaterials: what material or composite material is the best for which application and how to modify the properties of these materials in the desired way. This study contributes to the fundamental knowledge of the two-dimensional nanomaterial molybdenum diselenide, MoSe2. We investigate the thermostability of this material by in-situ transmission electron microscopy. This technique allows to do real-time, atomic scale imaging while heating up to over a thousand degrees Celsius. At this high temperatures, starting from around 850 C the material decomposed by the selenium sublimation into the vacuum of the elctron microscope. At slightly more moderate temperatures (750 C - 850 C) only a signifi?cant amount of selenium sublimates when irradiated by the electron beam. This moderate etching caused spontaneous formation of nanowire networks. The nanowires can be connected to either pristine MoSe2 or elemental molybdenum. Density Functional Theory calculations are used to assist the interpretation of the results. Based on these calculations, many phases are concluded to be energetically unstable, except for two two-dimensional phases (the H-phase and the T-phase) and the observed Mo6Se6 nanowire.