Controllable Preparation And Growth Mechanism Of Molybdenum Distelluride Nanofilm

Two-dimensional（2D）transition metal dichalcogenides（TMDs）have been regarded as promising material candidates in the next-generation electronics,optoelectronics and memory devices due to their tunable bandgap and novel physical properties.Very recently,2D Mo Te₂has attracted much interest owing to potential applications in phase-change memory and storage devices because of the small energy difference between 1T’and 2H phases.2H phase Mo Te₂has a tunable bandgap of0.88-1.1 e V depending on thickness and exhibits strong spin-orbit coupling effect,which makes it an excellent candidate for spintronic and near-infrared optoelectronic devices.1T’Mo Te₂has demonstrated to be a semimetal with superconductivity,which exhibits potential application for quantum computation.Therefore,controllable selective growth of 1T’,2H atomically thin Mo Te₂nanostructures are very important to achieve high performance of Mo Te₂-based devices.But mixed-phase Mo Te₂materials were easily prepared due to the small energy difference between the semiconducting 2H and metal 1T’phases.Precisely controlled phase transition of Mo Te₂nanostructures is still a considerable challenge.In this thesis,the main contents are as follow:1.The selective growth of pure 1T’Mo Te₂film and the micro/nanostructures of the system were systematically characterized.Moreover,the corresponding thickness of 1T’Mo Te₂can be effectively controlled from 2.2 nm to 18.8 nm by adjusting the space-confined height.Both experimental and theoretical simulation results confirm that the space-confined CVD method provides a stable environment to precisely control the uniformity and thickness of as-prepared Mo Te₂films.Interestingly,the thickness of 1T’Mo Te₂film can be also reduced when the growth temperature and growth time were decreased.Compared to Mo O₃powder precursor,we believe that the uniform supply of precursor by using Mo O₃foil promotes the growth of large-area atomically thin 1T’Mo Te₂film.Our experimental results demonstrate that this strategy is reliable for the growth 1T’Mo Te₂film on various substrates.2.When the growth temperature was increased to 740℃and maintained for 50min,centimeter-scale pure 2H Mo Te₂film was obtained.The AFM,KPFM and Raman mapping characterizations indicate the uniformity of 2H Mo Te₂film.The thickness of Mo Te₂film was reduced from 46.2 nm to 4.3 nm with the space-confined height ranging from 1 mm to 4 mm.To further investigate phase transition mechanism,systematic growth temperature and growth time were systematically investigated by employing the phase transformation reaction speed and nucleation to explain our experimental results.3.The electrical transport properties of 1T’and 2H Mo Te₂films were investigated by conductive atomic force microscope and Mo Te₂-based thin-film field-effect transistors.