Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore 637371, Singapore.
Nanoscale. 2017 Jun 8;9(22):7533-7540. doi: 10.1039/c7nr02028g.
Due to the easy intralayer gliding and weak interlayer van der Waals interaction in transition metal dichalcogenides (TMDs), ion (particularly Li) intercalation has been used to modify and tune their atomic structures to obtain the desired optical, electronic and chemical properties for future optoelectronics and energy storage applications. A good understanding of the transformative structures during intercalation is critical. In this paper, we investigate the structural transformation dynamics of 2H-MoS using electrochemical Li intercalation for 2H-MoS. The introduction of Li changes the local symmetry of the MoS in favor of the dT phase, clearly indicated by the appearance of Raman peaks of the dT phase. Further Li insertion causes the samples to become single-layer-like, characterized by the disappearance of the 32 cm Raman peak. We also observe for the first time that the photoluminescence (PL) emission gradually redshifts with decreasing intensity, followed by eventual vanishing of the PL peak in the dT-MoS phase. By the nudged elastic band (NEB) calculations, we propose the 2H-1T-dT phase transition mechanism of MoS for Li intercalated samples. Our claims are supported by high resolution-transmission electron microscopy (HR-TEM). Our study deepens the understanding of the phase transition dynamics upon lithium intercalation, which is of great value to possible optoelectronic devices based on the phase engineering of TMDs. The new Li-stabilized dT-MoS phase does not possess inversion symmetry and may present a feasible way to achieve Weyl state tuning in a single material via phase engineering.
由于过渡金属二硫属化物（TMDs）的层间易于滑动和较弱的范德华相互作用，离子（特别是 Li）的嵌入已被用于修饰和调整其原子结构，以获得未来光电子学和储能应用所需的理想光学、电子和化学性质。深入了解嵌入过程中的结构转变至关重要。在本文中，我们研究了电化学 Li 嵌入 2H-MoS 时 2H-MoS 的结构转变动力学。Li 的引入改变了 MoS 的局部对称性，有利于 dT 相，这一点可以通过 dT 相的 Raman 峰的出现清楚地表明。进一步的 Li 插入使样品变得类似于单层，其特征是 32cm Raman 峰的消失。我们还首次观察到光致发光（PL）发射逐渐红移，强度降低，随后在 dT-MoS 相中 PL 峰最终消失。通过推牛顿弹性带（NEB）计算，我们提出了 Li 嵌入样品中 MoS 的 2H-1T-dT 相变机制。我们的主张得到了高分辨率透射电子显微镜（HR-TEM）的支持。我们的研究加深了对锂嵌入过程中相变动力学的理解，这对于基于 TMDs 相工程的可能光电子器件具有重要价值。新的 Li 稳定的 dT-MoS 相不具有反转对称性，可能通过相工程在单个材料中实现 Weyl 态调谐的可行方法。
