Selective Fabrication of Monolayer 1H- and 1T'-WTe2

We selectively fabricated monolayers of octahedral (1H) and distorted trigonal (1T') WTe2 on graphene/SiC(0001) by controlling the substrate temperature during epitaxy. Angle-resolved photoemission spectroscopy, combined with first-principles band-structure calculations, has revealed several drastic differences between these two polymorphs. The 1T' phase exhibits a semiconducting character with a nearly-zero energy gap, while the 1H phase shows a large band gap and the band splitting at the K/K' point. The present results pave a pathway toward developing nanoelectronic devices based with WTe2.