Wang Hongguang, Zhang Jiawei, Shen Chen, Yang Chao, Küster Kathrin, Deuschle Julia, Starke Ulrich, Zhang Hongbin, Isobe Masahiko, Huang Dennis, van Aken Peter A, Takagi Hidenori
Max Planck Institute for Solid State Research, Heisenbergstr. 1, 70569, Stuttgart, Germany.
Department of Materials and Earth Sciences, Technical University of Darmstadt, Darmstadt, Germany.
Nat Commun. 2024 Mar 21;15(1):2541. doi: 10.1038/s41467-024-46934-0.
Two-dimensional (2D) van der Waals (vdW) materials offer rich tuning opportunities generated by different stacking configurations or by introducing intercalants into the vdW gaps. Current knowledge of the interplay between stacking polytypes and intercalation often relies on macroscopically averaged probes, which fail to pinpoint the exact atomic position and chemical state of the intercalants in real space. Here, by using atomic-resolution electron energy-loss spectroscopy in a scanning transmission electron microscope, we visualize a stacking-selective self-intercalation phenomenon in thin films of the transition-metal dichalcogenide (TMDC) NbSe. We observe robust contrasts between 180°-stacked layers with large amounts of Nb intercalants inside their vdW gaps and 0°-stacked layers with little detectable intercalants inside their vdW gaps, coexisting on the atomic scale. First-principles calculations suggest that the films lie at the boundary of a phase transition from 0° to 180° stacking when the intercalant concentration x exceeds ~0.25, which we could attain in our films due to specific kinetic pathways. Our results offer not only renewed mechanistic insights into stacking and intercalation, but also open up prospects for engineering the functionality of TMDCs via stacking-selective self-intercalation.
二维（2D）范德华（vdW）材料提供了丰富的调控机会，这些机会源于不同的堆叠构型，或通过在vdW间隙中引入插层剂而产生。目前关于堆叠多型性与插层之间相互作用的认识通常依赖于宏观平均探针，而这些探针无法在真实空间中精确确定插层剂的原子位置和化学状态。在此，通过在扫描透射电子显微镜中使用原子分辨率电子能量损失谱，我们可视化了过渡金属二硫属化物（TMDC）NbSe薄膜中的一种堆叠选择性自插层现象。我们观察到，在vdW间隙中有大量Nb插层剂的180°堆叠层与在vdW间隙中几乎检测不到插层剂的0°堆叠层之间存在明显的差异，它们在原子尺度上共存。第一性原理计算表明，当插层剂浓度x超过约0.25时，薄膜处于从0°到180°堆叠的相变边界，由于特定的动力学途径，我们在薄膜中能够达到这一浓度。我们的结果不仅为堆叠和插层提供了新的机理见解, 还为通过堆叠选择性自插层来设计TMDCs的功能开辟了前景。
