MBE growth of few-layer 2H-MoTe 2 on 3D substrates

Abstract MoTe 2 is the least explored material in the Molybdenum-chalcogen family. Molecular beam epitaxy (MBE) provides a unique opportunity to tackle the small electronegativity difference between Mo and Te while growing layer by layer away from thermodynamic equilibrium. We find that for a few-layer MoTe 2 grown at a moderate rate of ∼6 min per monolayer, a narrow window in temperature (above Te cell temperature) and Te:Mo ratio exists, where we can obtain pure phase 2 H -MoTe 2 . This is confirmed using reflection high-energy electron diffraction (RHEED), Raman spectroscopy and X-ray photoemission spectroscopy (XPS). For growth on CaF 2 , Grazing incidence X-ray diffraction (GI-XRD) reveals a grain size of ∼90 A and presence of twinned grains. In this work, we hypothesis the presence of excess Te incorporation in MBE grown few layer 2 H -MoTe 2 . For film on CaF 2 , it is based on >2 Te:Mo stoichiometry using XPS as well as ‘a’ and ‘c’ lattice spacing greater than bulk 2 H -MoTe 2 . On GaAs, its based on observations of Te crystallite formation on film surface, 2 × 2 superstructure observed in RHEED and low energy electron diffraction, larger than bulk c-lattice spacing as well as the lack of electrical conductivity modulation by field effect. Finally, thermal stability and air sensitivity of MBE 2H-MoTe 2 is investigated by temperature dependent XRD and XPS, respectively.