Key Laboratory for the Physics and Chemistry of Nanodevices and Department of Electronics , Peking University , 5 Yiheyuan Road , Beijing 100871 , PR China.
State Key Lab of Advanced Processing and Recycling on Non-Ferrous Metals , Lanzhou University of Technology , 287 Langongping Road , Lanzhou 730050 , PR China.
Nano Lett. 2019 Feb 13;19(2):857-865. doi: 10.1021/acs.nanolett.8b04065. Epub 2019 Jan 28.
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 MoC superconductor, a newly emerging member of the 2D TMC family. The 2D MoC superconductor shows a unique tilt-angle-dependent GB structure and electronic transport properties. Different from the reported 2D materials, the GB of 2D MoC 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.
石墨烯和二硫化钼的晶界（GBs）已被广泛证明对电子、热、光和机械性能有很强的影响。二维过渡金属碳化物（TMCs），称为 MXenes，是一类快速发展的新型二维材料，具有许多迷人的特性和广阔的应用前景。然而，二维 TMCs 的晶界结构及其对性能的影响尚不清楚。在这里，我们使用了具有像差校正功能的扫描透射电子显微镜结合电学测量，研究了具有高结晶度的二维 MoC 超导体的晶界特性，MoC 超导体是二维 TMC 家族中的一个新兴成员。二维 MoC 超导体表现出独特的倾斜角度依赖的晶界结构和电子输运性质。与报道的二维材料不同，二维 MoC 的晶界表现出独特的位错配置或锯齿图案，这取决于倾斜角度。更重要的是，我们发现了两个具有不同周期性结构和晶体取向的新的周期性晶界。对单个晶界的电学测量表明，晶界结构强烈影响输运性质。在正常状态下，随着倾斜角度的增加，在晶界区域观察到越来越强的电子局域化行为。在超导状态下，晶界处的临界电流大大减小，这与晶界处超导性的局部抑制有关。这些发现为二维 TMCs 的晶界结构和晶界对二维超导性的影响提供了新的认识，这将有助于通过晶界工程来调整二维 TMCs 的性质。
