Lateral junctions of transition metal dichalcogenides as ballistic channels for straintronic applications.

In the context of advanced nanoelectronics, two-dimensional semiconductors such as transition metal dichalcogenides (TMDs) are gaining considerable interest due to their ultimate thinness, clean surface and high carrier mobility. The engineering prospects offered by those materials are further enlarged by the recent realization of atomically sharp TMD-based lateral junctions, whose electronic properties are governed by strain effects arising from the constituents lattice mismatch. Although most theoretical studies considered only misfit strain, first-principles simulations are employed here to investigate the transport properties under external deformation of a three-terminal device constructed from a MoS2/WSe2/MoS2junction. Large modulation of the current is reported owing to the change in band offset, illustrating the importance of strain on the p-n junction characteristics. The device operation is demonstrated for both local and global deformations, even for ultra-short channels, suggesting potential applications for ultra-thin body straintronics.

Imaging Negative Charge around Single Vanadium Dopant Atoms in Monolayer Tungsten Diselenide Using 4D Scanning Transmission Electron Microscopy.

There has been extensive activity exploring the doping of semiconducting two-dimensional (2D) transition metal dichalcogenides in order to tune their electronic and magnetic properties. The outcome of doping depends on various factors, including the intrinsic properties of the host material, the nature of the dopants used, their spatial distribution, as well as their interactions with other types of defects. A thorough atomic-level analysis is essential to fully understand these mechanisms. In this work, the vanadium-doped WSe2 monolayer grown by molecular beam epitaxy is investigated using four-dimensional scanning transmission electron microscopy (4D-STEM). Through center-of-mass-based reconstruction, atomic-scale maps are produced, allowing the visualization of both the electric field and the electrostatic potential around individual V atoms. To provide quantitative insights, these results are successfully compared to multislice image simulations based on ab initio calculations, accounting for lens aberrations. Finally, a negative charge around the V dopants is detected as a drop in the electrostatic potential, unambiguously demonstrating that 4D-STEM can be used to detect and to accurately analyze single-dopant charge states in semiconducting 2D materials.

Ab initio quantum transport in polycrystalline graphene.

Synthesis techniques such as chemical vapor deposition yield graphene in polycrystalline flakes where single-crystal domains are separated by grain boundaries (GBs) of irregular shape. These structural defects are mostly made up of pentagon-heptagon pairs and represent an important source of scattering, thus strongly affecting electronic mobilities in polycrystalline graphene (PG). In the present article, first-principles simulations are performed to explore charge transport through a GB in PG using the Landauer-Büttiker formalism implemented within the Green's function approach. In ideal GB configurations, electronic transport is found to depend on their topology as already suggested in the literature. However, more realistic GBs constructed out of various carbon rings and with more complex periodicities are also considered, possibly inducing leakage currents. Finally, additional realistic disorder such as vacancies, a larger inter-connectivity region and out-of plane buckling is investigated. For specific energies, charge redistribution effects related to the detailed GB topology are found to substantially alter the transmissions. Altogether, the transport gap is predicted to be inversely proportional to the smallest significant periodic pattern and nearly independent of the interface configuration.