In-Situ Aberration Corrected Electron Microscopy Study of 2H-MoTe(2) Phase Transition
Transitional-metal dichalcogenides (TMDs) have attracted widespread research interests for nano-electronic and photovoltaic applications because of their novel structure and tunable properties. Among various TMDs, mono-layer 2H-MoTe2 is a potential channel material for field effect transistors (FETs). For practical MoTe2-based FET applications, there are still several critical issues such as low band gap energy, good contact and thermal stability that are to be resolved. Here, we present our recent in-situ heating study of 2H-MoTe2 by means of Scanning Transmission Electron Microscopy (STEM), specifically High Angle Annular Dark Field (HAADF) imaging and scanning tunneling microscopy (STM). Our study shows that MoTe2 can change from 2H phase to Mo6Te6 phase under by catalyzer free vacuum annealing. This Mo6Te6 phase is a new phase which has not been predicted by phase diagram. Its atomic structure consists of six central atoms of molybdenum surrounded by six atoms of tellurium. It has one dimensional nanowire morphology with about 0.8 nm in diameter. Density functional theory (DFT) calculation shows that individual Mo6Te6 nanowire phase is semiconducting with about 0.3 eV band gap, while the nanowire bundles are predicted to be metallic. The metallic property of these nanowire bundles has been confirmed by scanning tunneling spectroscopy (STS) and x-ray photoemission spectroscopy (XPS) measurements. The location and nature of individual atoms, phase transformation behavior, and theoretical calculations of various phases predicted will be presented and discussed in detail.