Growth and properties of semi-metallic and semiconducting phases of MoTe$_{\mathrm{2}}$ monolayer by molecular-beam epitaxy*

Hexagonal (2H) and distorted octahedral (1T') phases are the~two common structures of~monolayer MoTe$_{\mathrm{2}}$~showing, respectively, semiconducting and semi-metallic properties. The formation energies between the two structures of~MoTe$_{\mathrm{2}}$~are almost equal, so there is a high chance to tune the structures of MoTe$_{\mathrm{2}}$~and to bring in new applications such as phase-change electronics. In this work, we report growth of both 2H and 1T' MoTe$_{\mathrm{2}}$~ML by molecular-beam epitaxy (MBE) and demonstrate the tunability of the structural phases~by changing the growth conditions of MBE. We present experimental and theoretical evidences showing the important role of Te surface adsorption in promoting and stabilizing the otherwise metastable 1T'-MoTe$_{\mathrm{2}}$~during MBE.~By scanning tunneling microscopy and spectroscopy,~we also reveal~quantum dot states and quantum inter-valley~interference~patterns~in the 2H and 1T' domains, respectively.