Electronic structure of molecular beam epitaxy grown 1 T ′ -MoTe2 film and strain effect*

Abstract

Atomically thin transition metal dichalcogenide films with distorted trigonal ( 1 T ′ ) phase have been predicted to be candidates for realizing quantum spin Hall effect. Growth of 1 T ′ film and experimental investigation of its electronic structure are critical. Here we report the electronic structure of 1 T ′ -MoTe2 films grown by molecular beam epitaxy (MBE). Growth of the 1 T ′ -MoTe2 film depends critically on the substrate temperature, and successful growth of the film is indicated by streaky stripes in the reflection high energy electron diffraction (RHEED) and sharp diffraction spots in the low energy electron diffraction (LEED). Angle-resolved photoemission spectroscopy (ARPES) measurements reveal a metallic behavior in the as-grown film with an overlap between the conduction and valence bands. First principles calculation suggests that a suitable tensile strain along the a-axis direction is needed to induce a gap to make it an insulator. Our work not only reports the electronic structure of MBE grown 1 T ′ -MoTe2 films, but also provides insights for strain engineering to make it possible for quantum spin Hall effect.