Grain Boundaries and Tilt-Angle-Dependent Transport Properties of a 2D Mo₂C Superconductor

Abstract

The grain boundaries (GBs) of graphene and molybdenum disulfide have been extensively demonstrated to have a strong influence on electronic, thermal, optical, and mechanical properties. 2D transition-metal carbides (TMCs), known as MXenes, are a rapidly growing new family of 2D materials with many fascinating properties and promising applications. However, the GB structure of 2D TMCs and the influence of GB on their properties remain unknown. Here, we used aberration-corrected scanning transmission electron microscopy combined with electrical measurements to study the GB characteristic of highly crystalline 2D Mo2C superconductor, a newly emerging member of the 2D TMC family. The 2D Mo2C superconductor shows a unique tilt-angle-dependent GB structure and electronic transport properties. Different from the reported 2D materials, the GB of 2D Mo2C shows a peculiar dislocation configuration or sawtooth pattern depending on the tilt angle. More importantly, we found two new periodic GBs with different periodic structures and crystallographic orientations. Electrical measurements on individual GBs show that GB structure strongly affects the transport properties. In the normal state, an increasingly stronger electron localization behavior is observed at the GB region with increasing tilt angle. In the superconducting state, the magnitude of the critical current across the GBs is dramatically reduced, associated with local suppression of superconductivity at GBs. These findings provide new understandings on the GB structure of 2D TMCs and the influence of GB on 2D superconductivity, which would be helpful for tailoring the properties of 2D TMCs through GB engineering.

Recent Progress in Emerging Two-Dimensional Transition Metal Carbides

“…In the normal state, with the increase in grain boundary inclination angle, the critical current decreases by 1 to 2 orders of magnitude during the transition from superconducting state to resistive state. In the superconducting state, crossing the grain boundary will lead to the critical current to decrease significantly [207]. Jin et al prepared double-layer Mo 2 Ga 2 C by vacuum hot pressing.…”

Recent Advances in Growth of Transition Metal Carbides and Nitrides (MXenes) Crystals

“…Lattice defects are related to the superconducting enhancement mechanism of 2D α-Mo 2 C crystals. [132,133] MXenes have many excellent metal and ceramic properties due to the coexistence of both metal and covalent bonds. On the one hand, MXenes is widely used in jet engines, cutters, and protective coatings due to its high melting point, extremely high hardness, and good wear resistance.…”

“…Lattice defects are related to the superconducting enhancement mechanism of 2D α‐Mo 2 C crystals. [ 132,133 ]…”

Strain modulation on the spin transport properties of PTB junctions with MoC2 electrodes

“…21–24 However, most synthetic 2D materials are non-magnetic or weakly magnetic so far in nature. 25,26 Fortunately, the emergence of new two-dimensional materials 27–29 and the rapid development of rich modulation methods 30–33 and preparation methods 34–37 have broadened the idea for further development of molecular spintronic devices.…”