Selective Control of Phases and Electronic Structures of Monolayer TaTe₂.

Abstract

Transition metal dichalcogenide (TMDC) films exhibit rich phases and superstructures, which can be controlled by the growth conditions as well as post-growth annealing treatment. Here, the selective growth of monolayer TaTe₂ films with different phases as well as superstructures using molecular beam epitaxy (MBE) is reported. Monolayer 1H-TaTe₂ and 1T-TaTe₂ films can be selectively controlled by varying the growth temperature, and their different electronic structures are revealed through the combination of angle-resolved photoemission spectroscopy measurements (ARPES) and first-principles calculations. Moreover, post-growth annealing of the 1H-TaTe₂ film further leads to a transition from a <math xmlns="http://www.w3.org/1998/Math/MathML"> <semantics> <mrow><msqrt><mn>19</mn></msqrt> <mo>×</mo> <msqrt><mn>19</mn></msqrt> </mrow> <annotation>$\sqrt {19}{\times }\sqrt {19}$</annotation></semantics> </math> superstructure to a new 2 × 2 superstructure, where two gaps are observed in the electronic structure and persist up to room temperature. First-principles calculations reveal the role of the phonon instability in the formation of superstructures and the effect of local atomic distortions on the modified electronic structures. This work demonstrates the manipulation of the rich phases and superstructures of monolayer TaTe₂ films by controlling the growth kinetics and post-growth annealing.