Defect Agglomeration and Electron-Beam-Induced Local-Phase Transformations in Single-Layer MoTe₂

Abstract

Atom migrations in single-layer 1H-MoTe2 are studied with Cc/Cs-corrected highresolution transmission electron microscopy (TEM) at an electron energy of 40 keV using the electron beam simultaneously for material modification and imaging. After creating tellurium point defects and single Te vacancy lines, we observe their migration pathways across the lattice. Furthermore, we analyze local strain-dependent phase transformations from the 1H-to the 1T'-phase associated with single Te vacancy lines. Combining the experimental data with the results of first-principles calculations, we explain energetics and driving forces of point and line defect migration and the phase transformations due to an interplay of electron-beam-induced energy input, atom ejection, and strain spread. Our results enhance the understanding of defect dynamics in 2D transition metal dichalcogenides, which facilitates tailoring their local optical and electronic properties.

Structural and Chemical Modifications of Few-Layer Transition Metal Phosphorous Trisulfides by Electron Irradiation

“…Transmission electron microscopy (TEM) is a particularly useful tool for probing, − modifying, and tailoring − the properties of freestanding nanosheets with energetic electrons. This technique allows gaining chemical and crystallographic information from the materials, which can be correlated with each other even on an atomic scale using aberration-corrected (AC) high-resolution TEM (HRTEM). − A necessary condition is the preparation of pristine clean freestanding few-layer TMPTs samples, which recently was succeeded via polymer-assisted mechanical exfoliation .…”

Heterocontact-Triggered 1H to 1T′ Phase Transition in CVD-Grown Monolayer MoTe2: Implications for Low Contact Resistance Electronic Devices

“…with respect to the reference 1H phase. These findings are not surprising and consistent with the well-studied Te vacancy induced phase transition mechanism. , Our simulations suggest that Te vacancies work differently in AC and ZZ directions and are not the sole responsible for the observed PT; however, they importantly modify the energetic landscape and can be involved in the stabilization of the 1T′ phase in combination with other mechanisms. Reported reduced energy barrier values and lowered ground state energy difference between 1H and 1T′ phases indeed can be responsible for the avalanche effect observed experimentally.…”

“…Theoretically, different methods have been proposed such as electron/hole injection, ,,, electronic excitation, − strain, − annealing, , chalcogen or metal atom substitution, Li or H , doping, and Te vacancies creation. ,, Phase transition (PT) has been achieved on few-layers or bulk MoTe 2 via annealing, , ion liquid gating, electric field in vertical RRAM devices, Te vacancies creation, and Li intercalation . In the monolayer limit, investigations on 1H/1T′ phase transition are highly complicated by the air instability of monolayer 1T′, although promising initial results have been reported by adopting annealing, ionic liquid gating, , THz laser irradiation and Te vacancies creation . While developing approaches for triggering 1H–1T′ phase transition with external stimuli remains of undoubted interest for the realization of phase change devices, progressing in understanding and controlling the direct synthesis of lateral 1T′/1H heterostructures is the base for the development of low resistance contacts for electronics and optoelectronics and for devising novel device architectures.…”

Deep Understanding of Electron Beam Effects on 2D Layered Semiconducting Devices Under Bias Applications

“…[23,[30][31][32][33] On the other hand, in some monolayer TMD materials, some defects have been observed under e-beam irradiation with energy below 80 keV. [33][34][35] Accordingly, some defects can be generated even below the knock-out threshold energy (80 keV for MoS 2 ), but defect generations are insufficient to explain the strong negative shifts of I D -V G curves and the recoverable properties.…”